presspahn may be used for mechanical protection of winding insulation.

Wherever practicable, instrument, apparatus and machine coil windings, including wire wound
resistors, with the exception of those immersed in oil or compound, shall be thoroughly dried in a
vacuum or by other approved means and shall then be insulating varnish. Varnish with a linseed oil
base shall not be used.

No material of a hygroscope nature shall be used for covering coils. Where inter-leaving between
windings in coils is necessary, only the best manila paper, thoroughly dried, which permits
penetration by the insulating varnish or wax, shall be used.

1.25 L.V. Circuit Protection

Fuses are not to be used for protection of circuits below 1000V phase-to-phase, (Low Voltage).
All low voltage and dc circuit protection is to be provided by moulded case, or miniature circuit
breakers.

Link carriers and bases shall be of an approved manufacture and of such form and material so as to
protect persons from shock and burns in normal service and maintenance. Links and fixed contacts
shall be shielded to prevent inadvertent contact with live metal whilst the link is being inserted or
withdrawn.

The labeling of carriers and bases shall comply with IEC 60269 Identification labels fixed to
panels, boards and desks for MCBs and links shall describe their duty, voltage and rating.

1.25.1 Miniature Circuit Breakers

All miniature circuit breakers (MCBs) shall comply with IEC 60157 and be fitted with
over-current releases of both the thermal and instantaneous type. All MCBs supplied on
this contract shall be to short circuit category P2 of IEC 60157.

Single, two or three pole breakers may be used where appropriate and a trip of one pole
shall cause a complete trip of all associated poles. In addition the rating given of MCBs
supplied shall be confirmed as that appropriate to the enclosure provided.

The Contractor shall ensure satisfactory time and current grading with other associated
miniature circuit breakers or MCCBs.

1.25.2 Distribution Boards and Isolators

Distribution boards shall be provided throughout the plant for local distribution of
lighting, small power and air conditioning supplies. The lighting and small power circuits
may use a common distribution board.

Distribution boards shall be of 1 kV A.C., 1.2 kV D.C. rating and conform to IEC 60439.
All distribution boards shall be of the weatherproof enclosure type and shall be arranged
so that the door or cover can be locked in the closed position.

All triple pole and neutral boards shall provide satisfactory cable entry for all cables
which could be required for the number of circuit facilities provided and shall have the
neutral bar drilled for the full number single phase ways.

Each distribution board supplied from a remote location shall have a load breaking/fault
189
 making incoming isolating switch mounted adjacent to or as part of the distribution board.
Each distribution board shall have removable top and bottom (undrilled) gland plates.

Each circuit in every distribution board shall be numbered and identified by means of a
schedule attached to the interior of the door or cover of the board. The schedule shall be
legible and durable to the Project Manager’s approval.

Twenty-five percent spare ways shall be provided for future use.

1.26 Electrical Equipment, Instruments and Meters

All instruments and meters shall be fitted with glasses of low reflectivity and shall not cause pointer
deflection due to electro-static charging through friction.

All indicating instruments shall be of the flush mounted pattern with dust and moisture proof cases
complying with BS. 2011, Classification 00/50/04, and shall comply with BS. 89 or IEC 60051.

Unless otherwise specified, all indicating instruments shall have 95mm square cases to DIN
standard or equivalent circular cases.

Instrument dials in general shall be white with black markings and should preferably be reversible
where double scale instruments are specified.

Scales shall be of such material that no peeling or discoloration will take place with age under
humid tropical conditions.

The movements of all instruments shall be of the dead beat type.

Instruments shall be provided with a readily accessible zero adjustments.

The mounting height of the centre of all indicating instruments shall not exceed 2000mm.

A.C. ammeters for transformer, feeder or inter connector circuits, and D.C ammeter for all load
circuits except motors, shall have linear scales commencing at zero.

A.C and D.C ammeters for motor circuits shall have scales commencing at zero and with a
compressed overload portion for reading of the associated minor starting current.

D.C. ammeters for the main battery circuit of D.C systems shall have scales with positive and
negative ranges, labeled charge and discharge respectively.

Voltmeters for feeders and transformer circuits shall have expanded scales to display the nominal
service voltage ± 20%.

Wattmeter for feeders shall have linear positive and negative reading scales to be approved.

Varmeters for all circuits shall have linear positive and negative reading scales to be approved.

Integrating metering shall be provided where indicated on the specification drawings. These meters
shall be of the withdrawable flush mounted type and comply with the relevant parts of IEC 60521
and BS 5685, Class 1.0 accuracy and BS 37, Part 9. The meters shall include cyclometer dial type
registers.

Approved test terminal blocks of the three-phase type shall be provided for connecting in circuit
with each meter a portable testing meter.
190
If applicable, recording instruments shall be of an approved type, and unless otherwise specified,
shall have two chart speeds of 25 mm and 50 mm per hour available for selection by means other
than changing connections. They shall be complete with sufficient charts and inks for two years’
working.

All instruments, meters, recorders and apparatus shall be capable of carrying their full load currents
without undue heating. They shall not be damaged by the passage of fault currents within the rating
of the associated switchgear through the primaries of their corresponding instrument transformers.

All instruments, motors and apparatus shall be back connected and the metal cases shall be earthed.

All voltage circuits to instruments shall be protected by a fuse in each unearthed phase of the circuit
placed as close as practicable to the main connection.

All power-factor indicators in 3-phase circuits shall have the star point of their current coils brought
out to a separate terminal which shall be connected to the star point of the instrument current
transformer secondary windings.

All instruments and meters associated with multi-ratio CT’s shall be provided with sets of scales
etc. appropriate to each CT ratio. It shall be possible to replace the scales of instruments without
dismantling the instruments or interfering with any tropicalization finish.

The Contractor shall provide electrical instrument and meter schedules to include, manufacturer,
type, designation, current and voltage rating, accuracy class and circuit designation.

All equipment shall be colored “NEMA Standard Grey 70” unless otherwise specified by the
Project Manager.

1.27 Control and Selector Switches

Control switches shall be of the three-position type with a spring return action to a central position
(and without a locking feature).

Circuit breakers shall have control switches which shall be labeled open/N/close or (O/N/I and
arranged to operate clockwise when closing the circuit breakers and anti-clockwise when opening
them, and shall be of the pistol grip type.

Control switches of the discrepancy type shall be provided where specified. Such discrepancy
control switches shall be arranged in the lines of the mimic diagram on the switchgear panels. Such
switches shall include lamps and be of the manually operated pattern, spring loaded such that it is
necessary to push and twist the switch past its indicating position for operation. The lamp shall be
incorporated in the switch base and shall flash whenever the position of the circuit breaker is at
variance with the position indicated by the control switch. Hand dressing of the control switch to
the correct position shall cause the lamp to extinguish.

Selector switches shall be of the two or more position type as required, and have a stay-put action
to remain in any selected position which shall be lockable (separate padlocks each with duplicate
keys should be provided). Each position of the selector switches shall be suitably labeled to signify
their function. The switch handle shall be of the pistol grip type to the approval of the Project
Manager.

It shall not be possible at any time to operate any switchgear equipment from more than one

191
location simultaneously, and suitable lockable selector switches shall be provided to meet this
requirement.

The contacts of all control and selector switches shall be shrouded to minimize the ingress of dust
and accidental contact, and shall be amply rated for voltage and current for the circuits in which
they are used.

1.28 Auxiliary Switches

Auxiliary switches shall be to approval and contacts shall have a positive wiping action when
closing.

All auxiliary switches, whether in service or not in the first instance, shall be wired up to a terminal
board and shall be arranged in the same sequence on similar equipment.

Auxiliary switches mechanically operated by the circuit breakers, contactors, isolators, etc. shall be
to approval and contacts mounted in accessible positions clear of the operating mechanism of the
circuit breaker, contactor, isolator, etc., and they shall be adequately protected against accidental
electrical shock.

Auxiliary switches shall be provided to interrupt the supply of current to the trip coil of each circuit
breaker and contactor immediately the breaker or contactor has opened. These auxiliary switches
shall make before the main contacts, during a closing operation.

A minimum of four spare auxiliary switches, two normally open, two normally closed shall be
provided for each circuit breaker, and contactors and also for isolators.

1.29 Alarm Equipment

Where an alarm system is specified, it shall consist of an initiating device, a display unit and push
buttons mounted on the front of the appropriate control panel, together with a continuously rated
audible warning device flasher unit and relays. The relays shall wherever possible, be mounted
inside the same panel; where the number of alarms to be displayed makes this impracticable, a
separate alarm relay cubicle or cubicles will be considered as an alternative.

Where it is necessary to differentiate between the urgency of alarms then various approved alarm
tone devices shall be provided in this Contract. In addition and where specified an alarm beacon to
the approval of the Project Manager shall be provided.
The display unit shall consist of a rectangular frame or bezel enclosing the required number of
individual facias, each of which shall be preferably approximately 32mm x 25mm in size. Each
facia shall be in the form of a window inscribed with the specified legend, describing the fault
condition to be indicated. Lamps shall not illuminate adjacent windows.

At least 3 spare ways shall be provided on each display unit. All unused ways in a display unit shall
be fully equipped and the alarm system designed to enable these ways to be utilized at a future date.

Alarm relays shall be of a type to the approval of the Project Manager, arranged to plug into fixed
bases, either singly or in groups and have positive means of retaining them securely in the service
position, the bases being mounted on racks or frames which shall be hinged to allow them to be
swung clear of the sides of the panel or cubicle in which they are installed in order to provide ready
access.

The type of wiring used for internal connections between alarm facias and their relays and between

192
relays and terminal blocks, shall generally comply with these requirements with the following
exceptions:-

(i) Single-strand wire, not less than 0.85 mm in diameter may be used.

Soldered terminations will be acceptable

External connections for alarm circuits will in general be run in multi-core cables having a larger
core size than that referred to above. This will necessitate special terminal blocks, if soldered
terminations are used, in which case the internal and external terminations of each pair shall be
joined by a removable link. Samples of the type of wire and terminal block to be used for alarm
connections shall be submitted for the Project Manager’s approval.

The operation of the alarm system shall be as follows:-

When an external alarm indicating contact closes the audible warning shall sound continuously and
the appropriate facia shall be illuminated by a flashing light at a frequency which allows the
inscription to be easily road.
An ‘Accept’ push-button shall be provided on or near the display unit, which when pressed, shall
silence the audible signal and cause the facia to remain illuminated steadily.

The alarm circuit shall be designed to retain the indication after the re-opening of the initiating
contact, requiring a separate ‘Reset’ push button to be pressed before the alarm is cancelled.

A ‘Test’ push button shall be fitted close to the ‘Accept’ and ‘Reset’ buttons, to illuminate all the
facias on the associated display unit for as long as the ‘Test’ button is held depressed.

The operation of the ‘Accept’ button shall not preclude the receipt of further indications giving
more audible alarm and visual indications as the result of the operation of other sets of alarm
contacts.

Relays shall not be continuously energized when the alarm system is at rest.

For all alarm indication initiating device a spare set of voltage-free contacts shall be provided (this
may be by the use of auxiliary relays) and connected by cable to a suitable, approved marshalling
cubicle. These spare contacts will provide for the transmission of the alarm indication signals to the
remote Grid Control Centre.

The Contractor shall be responsible for providing all the alarms required for the safe and efficient
operation of the plant. General descriptions of alarms requirements are given in the specification
and the Contractor shall include any other alarms that are necessary due to the type of equipment
and design of the plant to the Project Manager’s approval.

1.30 Panels, Desks, Kiosks and Cubicles

1.30.1 General Requirements
Unless otherwise specified, panels, desks and cubicles, shall be of floor-mounted and free-
standing construction and be in accordance with the specified enclosure classification. All
control and instrumentation panels shall be identical in appearance and construction.
Panels shall be rigidly constructed from folded sheet steel of adequate thickness to support
the equipment mounted thereon, above a channel base frame to provide a toe recess.
Alternatively a separate kicking plate shall be provided.
Overall height, excluding cable boxes, shall not exceed 2.5 m. operating handless and
locking devices shall be located within the operating limits of 0.95m and 1.8m above floor
193
level. All panels shall be fitted with padlocks. The minimum height for indicating
instruments and meters shall be 1.5m unless otherwise specified.
All panels' desks and cubicles shall be vermin and insect proof. All cable entries to
equipment shall be sealed against vermin as soon as possible after installation and
connecting-up of the cables to the approval of the Project Manager.
Ventilation shall be provided for natural air circulation. All control equipment shall be
designed to operate without forced ventilation.
For outdoor equipment, metal to metal joints shall not be permitted and all external bolts
or screws shall be provided with blind taped where a through hole would permit the
ingress of moisture. All metal surfaces shall be thoroughly cleaned and particular care
taken during painting to ensure that both internally and externally a first class cover and
finish is achieved. For harsh environments, all nuts, bolts and washers shall be plated.
Door sealing materials shall be provided suitable for the specified site conditions. Doors
shall be fitted with handles and locks. The doors shall be capable of being opened from
within the panel without the aid of a key after they have been locked from the outside.
Hinges shall be of the life-off type. Seals shall be continuous or with only one joint.
The bottom and/or top of all panels shall be sealed by means of removable gasketted steel
gland plates and all necessary glands shall be supplied and fitted within the Contract.

Panels shall be suitably designed to permit future extension wherever appropriate or

specified without the need to dismantle the existing panels.Panels shall be “top entry”
types with respect to control cabling.
Each panel shall include rear access doors and door-operated interior lamp, and be clearly
labeled with the circuit titled at front and rear, with an additional label inside the panel.
Panels sections accommodating equipment at voltages higher than 110 V shall be
partitioned off and the voltage clearly labeled. Each relay and electronic card within
panels shall be identified by labels permanently attached to the panel and adjacent to the
equipment concerned. Where instruments are terminated in a plug and socket type
connection both the plug and the socket shall have permanently attached identifying
labels.
Instrument and control devices shall be easily accessible and capable of being removed
from the panels for maintenance purposes.
For suites of panels inter-panel bus wiring shall be routed through apertures in the sides of
panels and not via external multi-core cabling between the panels.

All panels, whether individually mounted or forming part of a suit, shall incorporate a
common internal copper earthing bar onto which all panel earth connections shall be

194
 made. Suitable studs of holes to the Project Manager’s approval shall be left at each end
of the bar for connection to the main station earthing system.

Earth connection between adjacent panels shall be achieved by extending the bar through
the panel sides and not by interconnecting external cabling.

Cubicles and cubicle doors shall be rigidly constructed such that, for example, door
mounted emergency trip contacts can be set so that mal-operation will not be possible due
to any vibrations or impacts as may reasonably be expected under normal working
conditions.

1.30.2 Indicating Lamps

All new indicators shall have a minimum continuous burning guaranteed life of 10,000
hours, at their rated voltage.

The Indicating lamps must be LEDs only and cluster LEDs for important functions
subject to approval of the Project Manager.

Indicators shall be easily replaceable from the front of the panel and shall be adequately
ventilated.LED indicators shall operate at not less than 20mA and red LED indicators
shall be of the high brightness types.

The lamps shall be clear and shall fit into a standard form of lamp holder. The rated lamp
voltage should be ten percent in excess of the auxiliary supply voltage, whether AC or
DC. Alternatively, low voltage lamps with series resistors will be acceptable, however
resistors shall be dimensioned to avoid damage due to heat.

The lamp glasses shall comply with BS 1376 and BS 4099 or equivalent National
Standard and shall be in standard colours, red, green, blue, white and amber. The colour
shall be in the glass and not an applied coating and the different coloured glasses shall not
be interchangeable. Transparent synthetic materials may be used instead of glass,
provided such materials have fast colours and are completely suitable for use in tropical
climates.
Normally energized indicating lamps, if employed, shall in general be energized from the
station LVAC supply.

Lamps and relays incorporated in alarm facia equipment shall be arranged for normal
operation from the station battery, subject to the approval of the Project Manager.
Lamp test facilities shall be provided so that all lamps on one panel can be tested
simultaneously by operation of a common push-button. Where alarm facias are specified,
all alarm and monitoring indications (apart from circuit-breaker and disconnector position
indications) shall be incorporated in the facia.
Where specified every circuit breaker panel shall be equipped with one red and one green
indicator lamp, indicating respectively circuit closed and circuit open and an amber lamp
for indicating ‘auto-trip’. Where specified in the lines of mimic diagrams, indicating
lamps may be of the three-lamp single-aspect type.
All lamps shall be renewable from the front of panels without the use of special tools.
The variety of indicating lamps provided shall be rationalized to reduce maintenance and
spares requirements.

195
1.30.3 Anti-Condensation Heaters

All switchboards, panels, cubicles, motor control Centre and the like shall
incorporate electric heaters capable of providing movement of sufficient heated
air to avoid condensation. The power supply to the heaters shall be manually switched
by a two pole switch with red lamp. All heaters on multi-panel equipment shall be
controlled from a single point. The related equipment shall be designed to accept the
resulting heat input.

Bus wiring shall be incorporated in switchboards for supplying the heaters.

1.31 Panel Wiring and Terminal Boards

1.31.1 General

All electrical equipment mounted in or on switchgear, panels, kiosks, and desks, etc. shall
have readily accessible connections and shall be wired to terminal blocks for the reception
of external cabling.

All wiring shall be of adequate cross-sectional area to carry prospective short-circuit

currents without risk of damage to conductors, insulation or joints.

All cabling shall be of type CR or CK to BS 6231 unless the design of the plant requires
the cabling to withstand more onerous operating conditions in which case cabling shall be
suitable for these conditions. The minimum cross section of wire shall be 4 sq.mm for
all secondary wiring associated with current transformers of nominal secondary rating of
0.5 A or greater. The size of wiring for circuits other than CT secondary wiring shall be
not less than 2.5 sq. mm. Cross-sectional area, save as permitted in the specification.

The minimum strand diameter of copper or tinned copper flexible conductors shall be
0.20 mm for flexible and the minimum cross-sectional area shall be 0.5 sq. mm for all
cables. For wiring within panels on circuits not directly associated with circuit breaker
protection and control, and having a continuous or intermittent, load current of less than 1
amp, the use of smaller line down to 0.25 sq. mm will be permitted subject to Project
Manager’s Approval.

Where an overall screen is used, this shall be metallic screen or low resistance tape, with
drain wire as above.

Wiring shall be supported using an insulated system which allows easy access for fault
finding and facilitates the rapid installation of additional cables.

Small wiring passing between compartments which may be separated for transport shall
be taken in terminal blocks mounted near the top of each compartment, separately from
those for external cable connections.

Both ends of every wire shall be fitted with ferrules of insulating material complying with
BS 3858 or equivalent National Standard and engraved in black. The identification
numbering system used for the ferrules shall be to the approval of the Project Manager.

196
 Where new equipment must interface with existing equipment double ferruling shall be
employed if the two numbering system are not compatible.

Connections to apparatus mounted on doors, or between points subject to relative

movement, shall be made in cable type CK to BS 6231, arranged so that they are
subjected to torsion rather than bending.

1.31.2 Identification of Cable Cores

Where a wire or multi-core cable passes from one piece of equipment to another, e.g.
from a circuit breaker to a remote control panel, the Contractor shall ensure that the
identity of the wire is apparent at both ends and intermediate marshalling points by the use
of ferrules, which shall permit identification of the cable in accordance with the schematic
diagrams. The ferruling system to be adopted shall be a composite marking method to IEC
391 and BS 3858 as appropriate, giving functional information on the purpose of the
individual conductor plus markings at both-ends.

Should the Contractors normal practice be at variance with the requirements of this clause
he may submit details of the scheme proposed for consideration by the Project Manager.
The Project Manager is not obliged to accept the Contractor’s proposal.

Each core of multi-pair wiring shall be identified by color and terminal block
identification together with an identification tracer per bundle.

Permanent identification of all terminals, wires and terminal blocks shall be provided.
Each individual terminal block shall have independent terminals for incoming and
outgoing cabling.

1.31.3 Terminals and Terminal Boards

Terminal Assemblies shall be of the unit form suitable for mounting on a standard
assembly rail, to give the required number of ways. The units shall be spring retained on
the assembly fail. Each individual terminal block shall have independent terminals and
outgoing cabling.

End barriers or shields shall be provided for open sided patterns.

It shall be possible to replace any unit in an assembly without dismantling adjacent units.
Moulding shall be mechanically robust and withstand the maximum possible operating
temperatures and torque which may be applied to terminal screw. All live parts shall be
recessed in the moulding to prevent accidental contact.

Terminals shall be of the screw clamp type for lower current rating which compress the
conductor or termination between two plates by means of a captive terminal screw.
Contact pressure of screw clamp terminations shall be independent of each other. For
higher current ratings bolted type terminals are permitted. Current carrying parts shall be
non-ferrous and plated.

All terminals for “incoming” cabling shall have testing facilities, which permit the
examination of the state of the circuit without disconnecting the associated cabling.
Terminal blocks for current transformer secondary shall be fitted with shorting/disconnect
facilities.

197
 Terminal blocks for voltage transformers secondaries shall be isolatable.

Terminal blocks in telemetry marshalling cubicles shall be isolatable. The means of

isolation shall be fixed and give visual identification of the status of the terminal.

Not more than 1 wire shall be connected to each terminal and cross-connection facilities
shall be provided where numerous cores are to connected together.

Each terminal block, and every individual terminal shall be identified. The terminal
identification number shall be included on associated schematic and wiring diagrams.

The mounting rail may only be used to provide an earth connection, when firmly bonded
to the earth bar and to be approved by the Project Manager.

The Contractor shall submit samples of the terminal blocks/mounting rail assemblies
together with details of his proposed cabling/termination system to the Project Manager
for approval.
Adjacent terminals to which wires of different voltage, polarity or phase are connected
shall be separated by a protruding insulating barrier; this requirement also applies to
terminals carrying wires of the same voltage but originating from different sources.

Wires shall be grounded on the terminal boards according to their functions. Terminal
blocks for connections exceeding 110V shall be fitted with insulting covers.

Terminal blocks shall be mounted not less than 150 mm from the gland plates, and spaced
not less than 100 mm apart, on the side of the enclosure.

Sufficient terminals shall be provided to permit all cores on multicore cables to be

terminated. Terminals for spare cores shall be numbered and be located at such position as
will provide the maximum length of spare core. At least 10% spare terminals shall be
provided in all cases.

The tails of multi-core cables shall be bound and routed so that each tail may be traced
without difficulty to its associated cable. All spare cores shall be made off to terminals.

When two lengths of screened cable are to be connected at a terminal block (i.e. junction
box) a separate terminal shall be provided to maintain screen continuity.

Should the terminal block manufacturer recommend that specific types of terminal tools
are used (eg parallel sided screw/drivers) the Contractor shall provide three sets of these at
each sub-station site. In addition the Contractor shall provide 8 numbers, test leads of
minimum 1500 mm length which can be inserted into the test terminals of the terminal
blocks, at each sub-station. The test leads shall be capable of being ‘jumpered’ together
for multi-instrument use.

The use of pre-formed factory tested cable connections to field mounted marshalling
boxes shall be to the Project Manager’s approval.
1.32 Cable Boxes and Glands
Electrical equipment supplied under this contract shall be fitted with all necessary cable boxes and
glands which shall be complete with all required fittings. Boxes shall be of adequate proportions to

198
accommodate all cable fittings, including stress cones or other means of cable insulation grading,
and designed in such a manner that they can be opened for inspection where appropriate without
disturbing the gland plate of incoming cable.

Glands for termination of cables to outdoor equipment or indoor areas liable to water spray, hosing
or flooding shall incorporate provision for sealing against ingress of moisture or dust, and shall
comply with the requirements of BS 6121 for sealing.

Removable gasketted steel gland plates shall be provided for multi-core cables and shall be
supported from the sides of the enclosures, as near to the floor or roof as possible while allowing
adequate space both above and below the plate for manipulation of the cable and gland. Gland
plates for marshaling boxes shall be in the form of removable gasketted steel plate, forming part of
the underside of the box.

The terminals for 3 phase cables shall be clearly marked with the phase colours (approved
designations) to enable the cables to be terminated in the correct sequence.

Filling and venting plugs where required, shall be positioned so as to avoid the possibility of air
being trapped internally and adequate arrangements shall be made for expansion of compound etc.
There shall be no possibility of oil entering the cable box from an associated oil filled
compartment. Cable sealing ends shall be arranged to project at least 25mm above the gland plate
to avoid moisture collecting in the crutch.

Any chamber which is to be compound filled shall be clean and dry and at such a temperature
before filling that the compound does not solidify during the filling process. Filling orifices shall be
sufficiently large to permit easy and rapid filling.

All cable boxes shall be designed to withstand the high voltage D.C. cable tests prescribed in BS
6346, BS 6480 and IEC 60055 as appropriate.

If applicable, cable boxes for paper-insulated cables shall be complete with universal tapered brass
glands (insulated from the box in an approved manner and including an island layer for testing
purposes.

Even single core cables are used, particularly for currents in excess of 500 A, adequate steps must
be taken to minimize the effects of eddy currents in the gland and bushing-mounted plate.

Cable glands for extruded solid dielectric insulated cables (PVC, EPR, and XLPE) shall be of the
compression type and as specified in BS 6121.

Approved glands shall be used on MICC cables

Glands for armored or screened cables above 240 sqmm shall be provided with an integral
heavy duty earthing lug capable of carrying the full earth fault current for a period not less than 1
second without deterioration.

Cable lugs and terminations for the receipt of all power control and instrumentation cable cores
shall be provided.

Cable boxes for the termination of elastomeric cables up in 33 kV nominal service voltage shall be
designed and dimensioned to provide adequate insulation in air for cables. Clearance and creepage
distances shall be adequate to withstand the specified alternating current voltages and impulse

199
voltages for service under the prevailing site conditions. The performance is to be met without the
use of insulating ‘boots’ shrouds orany other material fitted over or between the cable terminations
apart from permanently fitted barriers forming part of the switchgear or cable box.

Means shall be provided for preventing accumulation of dirt, dust, moisture, vermin or insects such
as to maintain the anticipated life of the equipment. The Contractor shall ascertain the means by
which elastomeric cables are to be terminated and shall provide such information or instructions as
necessary to any other contractor or sub-contract or to ensure compliance with this clause.

The cable crutch within a cable box or equipment panel shall be protected by the use of a heat-
shrink plastic ‘udder’ places over the conductors and crutch.

1.33 Joints and Gaskets

All joint faces are to be flat and parallel to the approval of the Project Manager and arranged
to prevent the ingress of water or leakage of oil with a minimum of gasket surface exposed to
the action of oil or air.

Oil-resisting synthetic rubber gaskets are not permissible, unless the degree of compression is
accurately controlled. For gaskets of cork or similar, oil resisting synthetic rubber may be used as a
bonding medium. No joints are allow in gaskets.

1.34 Junction, Termination Marshaling Boxes, Operating Cubicles etc

All junctions, termination and marshaling boxes shall be of substantial sheet steel construction,
having enclosure classification in accordance with the specification and fitted with external fixing
lugs and finished in accordance with this Specification for cleaning, painting and finishing.

The boxes shall allow ample room for wiring, with particular regard to the deployment of wires
from the point of entry.

Outdoor boxes shall have internal anti-condensation heaters and stay bars fitted to doors. Indoor
boxes shall be designed such that any condensed water cannot affect the insulation of the terminal
boards or cables. No cables shall be terminated into the top of outdoor boxes unless specifically
approved by the Project Manager.

Each box shall be complete with suitably inscribed identification labels.

Any outdoor boxes, cubicles etc containing instruments or meters shall have glazing suitable to
permit the visual examination of these.

Covers shall be arranged for padlocking and padlocks with keys shall be supplied. Cast iron boxes
shall have bolted lids requiring the use of special keys or spanners for removal.

All boxes shall be provided with adequate earthing bars and terminals.

Notwithstanding information supplied by the Project Manager, the Contractor shall, as each box is
completed or at intervals as requested by the Project Manager, supply to the Project Manager
copies of accurate termination or destination charts showing the as-fitted arrangement of cables and
cores in each box. The Contractor shall, following the Project Manager’s approval, fit one plastic
laminated copy of the appropriate chart to the interior of each box.

200
1.35 Conduit and Accessories
Conduit, accessories and trunking instal
lation shall comply with the latest issue of the Institution of Electrical Engineers Regulations for
the Electrical Equipment of Buildings, unless otherwise approved by the Project Manager. In
addition installation shall also comply with all local electricity regulations.

Unless otherwise approved, all conduit and conduit fittings shall be galvanized, of heavy gauge
steel, screwed, solid drawn or weld type complying with IEC 60423 and IEC 60614.

No conduit smaller than 19 mm outside diameter shall be used.

Standard circular boxes or machined face heavy-duty steel adaptable boxes with machined heavy
type lids shall be used throughout. For outdoor mounting all boxes shall be galvanized,
weatherproof and fitted with external fixing lugs.

Conduit terminations shall be fitted with brass bushes.

The use of running threads, solid elbows and solid tees will not be permitted.

Conduit ends shall be carefully reamed to remove burrs. Draw-in boxes shall be provided at
intervals not exceeding 10m in straight-through runs.

Conduit runs shall be in either the vertical or horizontal direction unless otherwise approved and
shall be arranged to minimize accumulation of moisture. Provision for drainage shall be made at the
lowest points of each run.

Conduits shall be supported on heavy galvanized spacer saddles so as to stand off at least 6 mm
from the fixing surface.

Provision shall be made for the support of internal conductors in instances where the length of the
vertical run exceeds 5m.

All conduits run in any circuit are to be completed before any cables are pulled in.

Flexible metallic conduit shall be used where relative movement is required between the conduit
and connected apparatus, and a separate copper connection provided to maintain earth continuity.

The maximum number of cables in any conduit shall be in accordance with the latest issue of the
IEE Regulations for the Electrical Equipment of Buildings.

1.36 Trunking
Steel trunking etc. may be used for running numbers of insulated cables or wires in certain
positions to the approval of the Project Manager. The trunking thickness shall not be less than 1.2
mm.

1.37 Push-Buttons and Separately Mounted Push-Button Stations

Push-buttons shall be shrouded or well recessed in their housings in such a way as to minimize the
risk of inadvertent operation. The colour of push-buttons shall be black unless otherwise required
by the Project Manager.
Push-button stations supplied as loose equipment shall be of the metal clad weatherproof type
suitable for wall or bracket mounting.Each push-button station shall be clearly labeled showing the
duty or drive to which it is applicable.

201
1.38 Drawings, Diagrams and Calculations
1.38.1 General
The term “drawing” shall also include diagrams, schedules, performance curves, and
calculations etc., required for the comprehensive design of the works. The Contractor
shall be responsible for the provision of all drawings required for the various stages of the
contract. All drawings, apart from workshop drawings, shall be submitted to the Project
Manager for his recommendation and final approval by the concerned committee of
BREB, in accordance with an approved program. The Contractor shall ensure that
drawings are submitted for approval in good time such that they may be approved within
the specified period prior to the manufacture or construction commencing. Further
adequate time must be allowed by the Contractor to permit any comments made by the
Project Manager to be incorporated. Any works performed prior to approval of drawings
by the concerned committee of BREB will be entirely at the Contractor’s own risk
including any delays that may result from modifications being found to be necessary by
the Project Manager.
The Contractor shall be fully responsible for obtaining any drawing or data of existing
plant and installations that he requires in order to carry out the works, and shall also be
responsible for verifying that any drawings of existing plant and installations are accurate.
The Contractor shall provide suitable drafting and other staff on site that he requires
investigating and producing any drawings that he requires of existing equipment and
installations in order to carry out the works. Any cost associated with these requirements
is deemed to be included in the contract price.

Where existing installations have been modified or extended the Contractor shall provide
complete new sets of drawings. In this respect the Contractor shall provide drawings
detailing both the existing and new works and shall not limit the scope of the drawings to
the new works only.

5 (Five) sets of As-built drawings together with operation and maintenance manual of the
equipment installed shall be submitted.

1.38.2 Format

Drawings are to be submitted for approval on paper prints, folded to A4 size with the
project title block and drawing numbers fully visible.

All drawings are to be submitted on “A” series paper to ISO/5457. The maximum size of
drawings shall be A1 except for site survey and layout drawings which may be submitted as
A0 size sheets, if necessary, to accommodate details on a scale of 1:100. Single line
diagrams and schematic drawings shall preferably be on a maximum sheet size of A2. All
dimensional drawings shall be to the following scales and fully detailed.
1:1, 1:2, 1:5, 1:10 and factors of 10 thereof.

202
 Drawings symbols shall be in accordance with IEC 60117.
All drawings are to be submitted in Auto Cad format in CDR Disks.
Drawing titles shall clearly identify the specific function of the drawings and where
appropriate the name of the site(s) to which the drawing applies.

1.38.3 Drawing Numbering and Revisions

The Contractor shall be responsible for adding the Employer’s drawing numbers to all
drawings prior to submittal. Following award of the contract, the Project Manager and the
Contractor will review the numbering system, familiarize each other with requirements,
and agree on the numbering system to be applied.

Comprehensive cross-references are to be included on drawings and the Contractor shall

include the Employer’s drawing numbers in the cross-references.

At each and every issue of a drawing the revision shall be raised, and details given in
revision boxes on the drawings. Comprehensive details of revisions are to be given and
phrases such as “REVISED”, “UPDATED”, “MODIFIED” or similar are not acceptable.

Reference to any drawing in communications shall include the Employer’s drawing

number.
1.39 Operating and Maintenance Manuals
2.

1.39.1 General

The Contractor shall be responsible for compiling operation and maintenance (O&M)
manuals for each section of the works and all equipments used.
Drafts of the manuals are to be submitted to the Project Manager at least six weeks prior
to the commencement of pre-energization commissioning checks on Site. Following
examination the Project Manager will forward copies of his comments to the Contractor to
action prior to issuing Final O&M manuals. Final O&M manuals are to be available on
site prior to the issue of the Taking over Certificate.
Handling, installation, storage and transit instructions, in accordance with BS 4884 part 1,
which shall form part of the manuals, are to be available on site prior to the arrival of the
Plant.
In addition to the compiled manuals, the Contractor shall submit copies of brochures and
other explanatory literature with drawings of the plant, which will assist the Project
Manager in approval of the drawings.

1.39.2 Contents

Operation and Maintenance manuals shall be prepared for the equipment supplied for the
substation. The content and presentation of the manuals shall conform in full with BS
4884 parts 1 and 2.

The O&M manuals are also to contain a complete drawing list appropriate to the
individual section of the works. The drawing list shall include the Project Manager’s
drawing numbers.

203
 Maintenance instructions for all plant shall cover preventive and corrective maintenance
procedures. For electronic or solid state control, protection equipment etc. details shall be
provided to enable individual circuit cards to be checked for correct operation and faults
to be traced, and repaired.

The Contractor shall provide proformas of the required maintenance record sheets for all
plant, which shall include cross-reference to the appropriate section of the O&M manuals
which detail how to perform the tasks required. Any other record sheets suitable for the
monitoring of the plant shall also be designed and provided.

1.39.3 Binders, Presentation

The information will be provided on A4 pages, with diagrams on throw-clear pages where
required to enable the text and diagrams to be refereed to simultaneously.
The front cover and spine of the manuals shall give the following information:
Project Title
Employer’s name
Contract number
Identification of the Section of the Works
Volume number and total number of volumes applicable
(e.g. volume 3 of 5 volumes)
Contractor’s company logo and name

The above shall also be provided on a flysheet inside the front cover of each volume.
Draft O&M manuals may be presented in unprinted covers.

Four copies of draft O&M manuals are to be provided to the Project Manager; following
approval 8 copies are to be provided to the Project Manager or his site Representative for
each section of the works.

1.40 Site Storage Facilities

The Contractor shall provide lockable cabinets in each of the individual substations, which are to
contain the following:

(a) One set of paper prints of the complete record of drawings for the section of the work.
These shall be arranged in a logical sequence in accordance with the drawing list contained
in the O&M manuals. Record drawings are to be grouped into labeled pockets or binders to
minimize disturbance in locating specific drawings. As-built drawings are to be stored in
these locations prior to the issue of record drawings.
(b) Two complete sets of O&M manuals
(c) Volumes of factory and site test reports/certificates
(d) Copies of maintenance log sheets, record sheets etc.
(e) Space for stationery and operators’ log books
These cabinets shall match other furnishings being provided in the substation and the location as
such items is to be included in the design of the substation layout.

204
1.41 Switchyard Cable Ducts and Conduits
A system of UPVC conduits (equipment to duct) and pre-cast concrete ducts shall be used for control
and LV cabling between switchyard equipment and the control building. Entry to the control/
protection panels in the building shall be via the top of the panels and a suitable sealing arrangement.

HV cabling between the transformers and switchgear panels shall be installed in concrete ducts in the
switchyard and within the building. HV Cabling between the control building and the feeder
termination poles shall be direct buried outside the building.

205
 SCHEDULE -A

PARTICULAR SPECIFICATIONS

206
 TABLE OF CONTENTS

Description Page No
Introduction 180
Power Transformers 181
Technical Requirement and Guarantee Schedule
(a) OLTC Type 20/28 MVA 33/11.55 K, 50 Hz Power Transformers 219
(b) OLTC Type 33/11.55 kV 10/14MVA Power Transformers 222
(c) 33 kV Surge Arrester, Station Class 224
(d) 11 kV Surge Arrester, Station Class 225
(e) 33/0.415 kV, 3 Phase 200 kVA Station Transformer 226
33 kV Outdoor Vacuum Circuit Breaker 227
Technical Requirement and Guarantee Schedule
(f) 33 kV Outdoor Type Vacuum Circuit Breaker (VCB) 241
(g) 33 kV Control and Energy Metering Panel 243
(h) Indication meter 245
(i) 33 kV Current Transformer (CT) 246
(j) 33 kV Voltage Transformer (VT) 247
11 kV Indoor Vacuum Circuit Breaker 248
Technical Requirement and Guarantee Schedule
(k) 11 kV Switchgear and Control Equipment 258
36 kV Underground Power Cable 264
15 kV Underground Power Cable 271
500 mm² 11 KV XLPE Cable 278
Technical Requirement and Guarantee Schedule
(l) 11KV, 1-Core x 500 Sq. mm U/G XLPE Copper Cable 283
(m)Joining kits for 11 kV XLPE, 1-Core, 500 mm2 Copper Cable 285
Conductors and Connections 287
Disconnectors and Earthing Switches 288
Insulators 291
Technical Requirement and Guarantee Schedule
(n) 33 kV Isolator/ Earth Switch 293
(o) 11 kV Isolator 294
(p) 33 kV Double Break Switched Fuse 295
Substation Earthing Systems 296
Substation Battery and Battery Charger 300
Overhead Earthing Screen 303
Section VI. Employers Requirements 180

207
1.1 INTRODUCTION

This section describes the Particular Technical Requirements for the 33 kV outdoor switchgear, the
11kV indoor switchgear, the main 33/11.55kV OLTC Transformers and all associated substation
equipment, and shall be read in conjunction with the General Technical Requirements, Schedules
and Drawings in the specification. The latest edition of the relevant IEC, British or American
standard shall apply. Standards from other countries may be considered by the Project Manager if
equivalent to or better than the above relevant standards.

208
 PUBLICATION 916A-2014
BANGLADESH RURAL ELECTRIFICATION BOARD (BREB)
PEOPLE’S REPUBLIC OF BANGLADESH
STANDARD FOR SUB-STATION
OLTC TYPE THREE PHASE POWER TRANSFORMERS:
10 MVA & 20 MVA
PART-1: GENERAL
1. SCOPE

The transformers shall be suitable for continuous operation on a three-phase 50 Hz high voltage
transmission system as specified herein. .

The transformers shall be of the three phase oil immersed type and designed with particular
attention to the suppression of harmonic especially the third and fifth harmonics and to minimize
the detrimental effects resulting there from. All transformers shall be suitable for outdoor
installation on concrete bases and shall be designed to operate satisfactorily in parallel with each
other. The transformer shall conform in all respects to highest standards of engineering, design,
workmanship, this specification and the latest revisions of relevant standards at the time of delivery.

The cooling for the transformers shall be ONAN/ONAF as specified.

2. REFERENCES

2.1 British Standards

BS 61 Specification for threads for light gauge copper tubes and fittings
BS 3600 Specification for dimensions and masses per unit length of welded and
seamless steel pipes and tubes for pressure purposes
BS 4504 Circular flanges for pipes, valves and fittings (PN designated)
BS 6121 Mechanical cable glands
BS 6346 Specification tor PVC insulated cables for electricity supply
BS 6435 Specification for unfilled enclosures for the dry termination of HV cables
for transformers and reactors
BS 7354 Code of practice for design of HV open terminal stations
BS 7613 Specification tor hot rolled quenched and tempered wieldable plates

2.2 BS European Standards

BS EN 10029 Specification for tolerances on dimensions, shape and mass for hot rolled
steel plates 3mm thick and above.

2.3 IEC Standards

IEC 60076 Power transformers

IEC 60137 Insulated bushings for ac voltages above l000 V
IEC 60186 Voltage transformers
IEC 60214 On load tap changers
IEC 60228 Conductors of insulated cables

209
Section VI. Employers Requirements 182

IEC 60233 Tests on hollow insulators for use in electrical equipment

Specification for unused mineral insulating oils tor transformers and
IEC 60296
switchgear
IEC 60354 Loading guide for oil immersed power transformers
Supervision and maintenance guide for mineral insulating oils in electrical
IEC 60422
equipment
IEC 60529 Degrees of protection provided by enclosures
IEC 60551 Determination of transformer and reactor sound levels

3. CLIMATE DATA
Main climate data that must be taken into account for the goods will be the followings:

Climate : Tropical, intense sunshine, heave

Maximum Temperature rain : 450 C
Minimum Temperature : 030
Average daily Temperature C : 300
Average isokeraunic level C
Relative humidity : 80 days/ year
Average annual rain fall : 50-100% :
Maximum wind velocity 3454 mm
Altitude : 200 km/hour
: 300 meters above Sea level
Atmospherically, Mechanical and Chemical impurities: Moderately polluted
The information is given solely as a guide for Bid and no responsibility for its, Accuracy will be
accepted nor will any claim based on the above be entertained.
Transformer supplied under this Contract will be installed in tropical locations that can be
considered hostile to its proper operation. Particular problems that shall receive special
consideration relate to operation in a humid environment and presence of insects and vermin.
4. SYSTEM CONDITIONS
The equipment shall be suitable for installation in supply systems of the following characteristics:
Frequency 50 Hz
Nominal system voltages 33 kV
11 kV
400/230V
Maximum system voltages: 33 kV System 36 kV
11 kV System 13.2 kV
LV System 440V
Minimum LV voltage 360 V
Nominal short circuit levels 33 Kv System 31.5 kA
11 Kv System 31.5 kA
Insulation levels: 33 kV System 170kV
1.2/50 ms impulse withstand (positive 11 kV System 75 kV
and negative polarity)
Power frequency one minute withstand 33 kV System 70 kV
(wet and dry) 11 kV System 28 kV
LV System 3 kV
Neutral earthing arrangements 33 kV System solidly earthed
11 kV System solidly earthed
LV System solidly earthed

210
5. INSPECTION AND TESTING

During pre-delivery/ pre-shipment inspection; BREB’s inspection team will witness the following
test of not less than 10% of total quantity ready for delivery on random sampling basis (sample
selected by the inspection team) during factory test in manufacturer’s factory premises:

1. Measurement of turn ration test;

2. Vector group test (check of phase displacement)
3. Measurement of winding resistance;
4. Measurement of no load loss & no-load current;
5. Measurement of impedance voltage & load loss;
6. Dielectric withstands test;
7. Transformer oil test;
8. Temperature rise test.
9. Impulse test.

Besides BREB’s inspection team will perform some physical test of at least 10 (ten) % transformer
of on random sampling basis during factory test:

1. Transformer tank sheet thickness (top bottom & side);

2. Hot dip galvanization test as per standard BS-729 of all bolts & nuts connected with
transformer tank, conservator, radiator etc;
3. Dimension of bolted type bimetallic connector for H.T. and L.T. bushing;
4. Dimension of tanks;
5. Checking of creep age distance of HT/LT bushings.
6. Others visible parts as per approval drawing.

As and when the Employer is satisfied that any materials/equipment shall have passed the relevant
tests, the Employer/ Project Manager shall notify the Contractor in writing to that effect.

Should any inspected/tested goods fail to conform to the specification, the Employer shall have the
right to reject any of the items or complete batch if necessary. In that case the Contractor shall
replace the goods or make them good without any cost to the Employer. The inspection and testing
shall be carried out again and all costs thereof shall be borne by the Contractor.

Nothing in this clause shall in any way release the Contractor from any warranty or other
obligations under the Contract.

5.1 Type Tests:

Instructions to the Bidders: The following shall be regarded as type tests. The Bidder shall submit
all Type test reports from internationally recognized independent testing laboratory along with his/
her bid.

5.1.1 Type Tests (for Transformer):

(a) Test of temperature rise (for both ONAN and ONAF).

(b) Short circuit test.

211
 (c) Dielectric test: (Induced over voltage test, Lightning Impulse voltage withstand test,
Power frequency voltage withstand test)

Temperature Rise, Short Circuit and Dielectric test (Induced over voltage test, Lightning
Impulse voltage withstand test, Power frequency voltage withstand test) on one Transformer
of each type and size (i.e. same KVA, KV, AMPS, Frequency, Impedance, Weight of the
Core, Oil etc. with tolerance ±5%) of Transformer. These all type tests shall be done on
same Transformer.

5.1.2 HT Bushing type test:

Dry or wet power-frequency voltage withstand test;

Dry lightning impulse voltage withstand test;
Temperature rise test ;
Verification of thermal short-time current withstand;
Cantilever load withstand test;
Verification of dimensions.
5.2 Special Tests:

a) Noise level measurement, in accordance with IEC Publication 551 using a precision sound level
meter conforming to IEC Publication 651. In addition the test shall be repeated with narrow
band filters for the harmonic frequencies from 100Hz. up to 350 Hz.
b) Magnetic balance test.
c) Dissolve gas test (for transformer oil).
d) Harmonics measurement test.
e) Measurement of zero phase sequence impedance.

5.3 Routine Tests

The following shall be regarded as routine tests and shall be carried out on each transformer.

(a) Measurement of winding resistance at principal tap and two extreme taps.
(b) Voltage-ratio measurement and check of vector group.
(c) Measurement of the impedance voltage at principal tap and two extreme taps.
(d) Measurement of the load loss.
(e) Measurement of no-load loss and no-load current, including measurement of harmonics.
(f) Applied voltage test to all auxiliary circuits.
(g) Tests on on-load tap-changer (fully assembled on transformer).
(h) Induced over-voltage withstand test. The voltage applied shall be the relevant power
frequency voltage specified in the clause on Insulation Levels.
(i) Separate source voltage withstand test. The applied voltage shall be the relevant power
frequency voltage specified in the clause on Insulation Levels.
(j) Polarization index test (1 minute and 10 minute). Index shall be not less than 1.3.
(i) Dielectric withstands test;
(j) Transformer oil test;
(k) Lightning Impulse Voltage with Withstand test (minimum 2 nos. of each type of transformer
per lot)
(l) Temperature rise test (minimum 2 nos. of each type of transformer per lot)

212
5.3.1 Routine Test Sequence

The sequence of tests shall be:

(a) Winding resistance measurement, voltage ratio measurement and vector group check
(b) Separate source voltage withstand test, induced over-voltage withstand test, impulse
test.
(c) Impedance voltage and loss measurements.
(d) Tap changer test.
(e) Tests on auxiliary circuits.
(f) Temperature rise test.

The following tests on site will be carried out after plant is fully assembled:

(a) Ratio and vector group checks.

(b) Insulation resistance (HV-LV, HV-E, LV-E).
(c) Oil tests.
(d) Other necessary pre-commissioning tests.

The Contractor will be held responsible for any discrepancy or defect discovered during
these tests and shall rectify immediately on receipt of notification at no cost to the
Employer. The Contractor may at his own discretion witness site testing of transformers.

6. PACKING AND SHIPPING

6.1 Packing
The equipment and any supporting structures are to be transported adequately sealed against water
ingress. All accessories and spares shall be packed and securely clamped against movement in
robust, wooden, non returnable packing cases to ensure safe transit in rough terrain, cross country
road conditions and in heavy rains from the manufacturer's works to the work sites.
individual serial number;
employer’s name;
contract number;
destination;
a colour coded marking to indicate destination;
contractor’s name;
name and address of contractor;
description and numbers of contents;
manufacturer’s name
country of origin;
case measurements;
gross and net weights in kilograms; and
all necessary slinging and stacking instructions.
Each crate or container shall be marked clearly on the outside of the case to show TOP and
BOTTOM positions with appropriate signs to indicate where the mass is bearing and the correct
positions for slings. All component parts which are separately transported shall have permanent
identification marks to facilitate correct matching and assembly at site. Welded parts shall be
marked before welding. Six copies of each packing list shall be sent to the Employer prior to
dispatching the equipment.

213
6.2 Shipping

The Contractor shall be responsible for the shipping of all plant and equipment supplied from
abroad to the ports of entry and for the transport of all goods to the various specified destinations
including customs clearance, off loading, warehousing and insurance.

The Contractor shall inform himself fully as to all relevant transport facilities and requirements and
loading gauges and ensure that the equipment as packed for transport shall conform to these
limitations. The Contractor shall also be responsible for verifying the access facilities specified.

The Contractor shall be responsible for the transportation of all loads associated with the contract
works and shall take all reasonable steps to prevent any highways or bridges from being damaged
by his traffic and shall select routes, choose and use vehicles and restrict and distribute loads so that
the risk of damage shall be avoided. The Contractor shall immediately report to the Employer any
claims made against the Contractor arising out of alleged damage to a highway or bridge.

All transport accessories, such as riding lugs, jacking pads or blanking off plates shall become the
property of the Employer. All items of equipment shall be securely clamped against movement to
ensure safe transit from the manufacturer's facilities to the specified destinations.

The Contractor shall advise the storage requirements for any plant and equipment that may be
delivered to the Employer’s stores. The Contractor shall be required to accept responsibility for the
advice given in so far as these arrangements may have a bearing on the behavior of the equipment
in subsequent service.

6.3 Hazardous substances

The Contractor shall submit safety data sheets for all hazardous substances used with the
equipment. The Contractor shall give an assurance that there are no other substances classified as
hazardous in the equipment supplied. No oil shall be supplied or used at any stage of manufacture
or test without a certificate acceptable to the Employer that it has a PCB content zero. The
Contractor shall accept responsibility for the disposal of such hazardous substances, should any be
found.

The Contractor shall also be responsible for any injuries resulting from hazardous substances due to
non compliance with these requirements.

7. SUBMITTALS

7.1 Submittals required with the bid

The following shall be required with each copy of the bid:

completed technical data schedule;

descriptive literature giving full technical details with calculation of heat dissipation,
radiator arrangement, no-load loss, full load loss, short circuit withstand capability, with
considering flux density and current density of equipment offered for both ONAN and
ONAF;

214
 outline dimension drawing for each major component, general arrangement drawing
showing component layout and general schematic diagrams;
type test certificates, where available, and sample routine test reports;
detailed reference list of customers already using equipment offered during the last 5
years with particular emphasis on units of similar design and rating;
details of manufacturer's quality assurance standards and program and ISO 9000 series
or equivalent national certification;
deviations from this specification. Only deviations approved in writing before award of
contract shall be accepted;
list of recommended spare parts and consumable items for five years of operation
with prices and spare parts catalogue with price list for future requirements.

7.2 Submittals required after contract award

7.2.1. Program

Five copies of the program for production and testing.

7.2.2. Technical Particulars

Within 30 days of contract award five bound folders with records of the technical
particulars relating to the equipment. Each folder shall contain the following information:

general description of the equipment and all components, including brochures;

technical data schedule, with approved revisions;
calculations to substantiate choice of electrical, structural, mechanical component
size/ratings;
detailed dimension drawing for all components, general arrangement drawing showing
detailed component layout and detailed schematic and wiring drawings for all
components;
detailed loading drawing to enable the Employer to design and construct foundations for
the transformer;
statement drawing attention to all exposed points in the equipment at
which copper/aluminum or aluminum alloy parts are in contact with or in close
proximity to other metals and stating clearly what protection is employed to prevent
corrosion at each point;
detailed installation and commissioning instructions; at the final hold point
for Employer approval prior to delivery of the equipment the following shall be
submitted;
inspection and test reports carried out in the manufacturer's works;
operation and maintenance instructions as well as trouble shooting char
7.2.3. Operation and Maintenance instructions
The copy of installation and commissioning instructions and of the operation and
maintenance instructions and troubleshooting charts shall be supplied with each
transformer. The Contractor/ Supplier should provide detail drawing including specified
loss, ratio, impedance, tap position against primary voltage etc.
7.3 Drawings

Within 30 days of Contract commencement the Contractor shall submit, to the Project Manager for
recommendation and approval by the concern committee of the Employer, a schedule of the
drawings to be produced detailing which are to be submitted for “Approval” and which are to be
submitted “For Information Only”. The schedule shall also provide a program of drawing
submission, for approval by the concern committee of the Employer that ensures that all drawings

215
and calculations are submitted within the period specified above. All detail drawings submitted for
approval shall be to scale not less than 1:20. All important dimensions shall be given and the
material of which each part is to be constructed shall be indicated on the drawings. All documents
and drawings shall be submitted in accordance with the provisions of this specification and shall
become the property of the Employer. All drawings and calculations, submitted to the Employer,
shall be on international standard size paper, either A0, A1, A2, A3 or A4. All such drawings and
calculations shall be provided with a Contract title block, which shall include the name of the
Employer and Consultants and shall be assigned a unique project drawing number; the Contract
title block and project numbering system shall be agreed with the Employer. Script sizes and
thickness of scripts and lines be selected so that if reduced by two stages the alphanumeric
characters and lines are still perfectly legible so as to facilitate microfilming. For presentation of
design drawings and circuit documents IEC Publication 617 or equivalent standards for graphical
symbols are to be followed.

8. SHIPMENT AND DRYING OUT

8.1 Shipment

Each transformer, when prepared for shipment, shall be fitted with a shock indicator or recorder
which shall remain in situ until the transformer is delivered to Site. In the event that the
transformer is found to have been subjected to excessive shock in transit, such examination as is
necessary shall be made in the presence of the Project Manager.

Where practicable, transformers shall be shipped with oil filling to cover core and windings but,
when shipped under pressure of gas, shall be fitted for the duration of delivery to Site and for such
time there after as is necessary, with a gauge and gas cylinder adequate to maintain internal
pressure above atmospheric.

All earthing transformers shall be shipped full of oil.

8.2 Drying Out

All transformers shall be dried out by an approved method at the manufacturer's works and so
arranged that they might be put into service without further drying out on Site.

Clear instructions shall be included in the Maintenance Instructions regarding any special
precautionary measures (e.g. strutting of tap changer barriers or tank cover) which must be taken
before the specified vacuum treatment can be carried out. Any special equipment necessary to
enable the transformer to withstand the treatment shall be provided with each transformer.

9. APPROVAL PROCEDURE
The Contractor shall submit all drawings, documents and type test reports for approval in sufficient
time to permit modifications to be made if such are deemed necessary and resubmit them for
approval without delaying the initial deliveries or completion of the Contract work. The
Employer’s representative shall endeavor to return them within a period of four weeks from
the date of receipt. Three copies of all drawings shall be submitted for approval and three copies
for any subsequent revision. The Employer reserves the right to request any further
additional information that may be considered necessary in order to fully review the
drawings. If the Employer is satisfied with the drawing, one copy will be turned to the
Contractor marked with “Approved” stamp. If the Employer is not totally satisfied with the
drawing, then “Approved Subject to Comment” status will be given to it and a comment sheet
will be sent to the Contractor. If the drawing submitted does not comply with the requirements of
the specification then it will be given “Not Approved” status and a comment sheet will be sent

216
to the Contractor. In both these cases the Contractor will have to modify the drawing, update the
revision column and resubmit for final Approval. Following approval, twenty copies of the final
drawings will be required by the Employer within the time allocated for design and drawing
approval.

Any drawing or document submitted for information only should be indicated as such by the
Contractor. Drawings and documents submitted for information only will not be returned to the
Contractor unless the Employer considers that such drawing needs to be approved, in which case
they will be returned suitably stamped with comments.

The Contractor shall be responsible for any discrepancies or errors in or omissions from the
drawings, whether such drawings have been approved or not by the Employer. Approval given by
the Employer to any drawing shall not relieve the Contractor from his liability to complete contract
works in accordance with this specification and the condition of contract nor exonerate him from
any of his guarantees.

If the Contractor needs approval of any drawing within a period of less than four weeks in order to
avoid delay in the completion of supply, he shall advise the Employer when submitting the
drawings and provide an explanation of the document’s late submission. The Employer will
endeavor to comply with the Contractors timescale, but this cannot be guaranteed.

10. SURFACE TREATMENT

A full description of the corrosion prevention system proposed by the Contractor shall be given in
the Schedule and this is subject to acceptance by the Employer. This description shall include
details of surface preparation, rust inhibition, paint thickness, treatment of fasteners and painting of
surfaces in contact with oil.

All machining, drilling, welding, engraving, scribing or other manufacturing activities which would
damage the final surface treatment shall be completed before the specified surface treatment is
carried out. Any subsequent damage occurring to the surface treatment up to the final delivery and
offloading shall be made good by the Contractor.

10.1 Painting

All paints shall be applied on clean, dry surfaces under suitable atmospheric and other conditions in
accordance with the paint manufacturer’s instructions. All paints used shall be compatible with
each other and capable of being used as a system. The system shall be capable of performance for
five years in the environment specified without any need for maintenance. No consecutive coats of
paint shall be of the same shade. The minimum standards acceptable are:
Cleaning by shot blasting to Grade Sa 2.5 of ISO 8501-1.
All sheet steelwork shall be degreased, pickled and phosphate in accordance with IS
6005 - “Code of Practice for phosphate of iron and steel.”
All rough surfaces of coatings shall be filled with an approved two pack filler and
rubbed down to a smooth finish.
Interior surfaces of mechanism chambers, boxes and kiosks, after preparation, cleaning
and priming shall be painted with one coat of zinc chromate primer, one coat of
phenolic based undercoating, followed by one coat of phenolic based finishing paint to
white colour followed by a final coat of anti-condensation white paint of a type and
make to the approval of the Employer. A minimum overall paint film thickness of 150
microns shall be maintained throughout.
Exterior steel work and metalwork, after preparation and priming shall be painted with
one coat of zinc chromate primer, one coat of phenolic based under coating and two

217
 coats of micaceous iron oxide paint, then painted with a final coat of phenolic based
hard gloss finishing paint of the Light Grey Shade No 631 of IS 5, to provide an overall
minimum paint thickness of 200 microns.
10.2 Galvanizing
All galvanizing shall be carried out by the hot dip process, in accordance with Specification ISO
1460 or IS 2629. However, high tensile steel nuts, bolts and spring washers shall be electro
galvanized to service condition 4. The zinc coating shall be smooth, continuous and uniform. It
shall be free from acid spots and shall not scale, blister or be removable by handling or packing.
There shall be no impurities in the zinc or additives to the galvanic bath which could have a
detrimental effect on the durability of the zinc coating.

Before pickling, all welding, drilling, cutting, grinding etc. must be completed and all grease, paint,
varnish, oil, welding slag etc. completely removed. All protuberances which would affect the life of
galvanizing shall also be removed.

The weight of zinc deposited shall be in accordance with that stated in standard BS 729 and shall be
not less than 0.61 kg/sq. mtr with minimum thickness of 86 microns for items of thickness more
than 5 mm, 0.46 kg/ sq. mtr. (64 microns) for items of thickness between 2 mm & 5 mm and 0.33
kg/ sq. mtr (47 microns) for items less than 2 mm thick. Parts shall not be galvanized if their shapes
are such that the pickling solution cannot be removed with certainty or if galvanizing would be
unsatisfactory or if their mechanical strength would be reduced. Surfaces in contact with oil shall
not be galvanized unless they are subsequently coated with an oil resistant varnish or paint. In the
event of damage to the galvanizing the method used for repair shall be subject to the approval of
the Employer or that of his representative. Repair of galvanizing on site will generally not be
permitted.
The threads of all galvanized bolts and screwed rods shall be cleared of splitter by spinning or
brushing. A die shall not be used for cleaning the threads unless specifically approved by the
Employer. All nuts and bolts shall be hot dip galvanized. Partial immersion of the work shall not be
permitted and the galvanizing tank must therefore be sufficiently large to permit galvanizing to be
carried out by one immersion.
After galvanizing no drilling or welding shall be performed on the galvanized parts of the
equipment excepting that nuts may be threaded after galvanizing. To avoid the formation of white
rust, galvanized material shall be stacked during transport and stored in such a manner as to permit
adequate ventilation. Sodium dichromate treatment shall be provided to avoid formation of white
rust after hot dip galvanization.

218
 PART-2: TECHNICAL
11. TYPE OF TRANSFORMER

The transformers shall be double copper wound, three phase, oil immersed, 33/11.55 kV, 50 Hz
with on-load tap-changer for 10/14 MVA Transformer and 20/28 MVA Transformer

The transformers shall be naturally cooled type ONAN and forced cooled type ONAF.

12. RATED CAPACITY

The MVA ratings shall be 10/14 MVA and 20/28 MVA based on ONAN/ONAF. Each transformer
shall be capable of supplying its rated power continuously at all tap positions. The transformers
shall also be capable of delivering rated current at an applied voltage equal to l05% of the rated
voltage.
Each transformer shall be capable of supplying its rated power continuously under ambient
temperature conditions without the temperature rise of the top oil exceeding 55°C and without the
temperature rise of the windings as measured by resistance exceeding 60°C. The ambient
temperature conditions are as follows:

Maximum ambient temperature 45° C

Maximum daily average ambient temperature 35° C
Maximum yearly weighted average ambient temperature 32° C

13. VOLTAGE RATIO

Each transformer shall be supplied with an on load tap changer (as specified) connected to the high
voltage winding. The tap changer shall have 17 tap positions and shall be so arranged as to give
variations of transformation ratio in equal steps of 1.5% per step. The total range of the tap changer
shall be from +6 percent to -18.0 percent. Tap 5 shall be the principal tap and the transformation
ratio at tap 5 shall be 33.00 KV to 11.55 KV.

The no-load voltage ratios shall be as follows (for OLTC):

Tap No. High Voltage Low Voltage

1 34.98 kV 11.55kV
5 33.00kV 11.55kV
17 27.06kV 11.55kV

14. WINDING CONNECTIONS AND VECTOR GROUP

The transformers shall be connected in accordance with IEC Publication 76 as follows:

HV Winding : Delta connected.

LV Winding : Star connected.
Vector Group : Dyn 1

15. INSULATION LEVELS

The transformers shall be designed and tested to the following insulation levels:

219
 Line Power Frequency Lightning Impulse
Terminals Voltage (rms.) Voltage (peak)
33kV 70kV 170 kV (1.2/50 μ sec.)
11kV 28kV 75 kV (1.2/50 μ sec.)

The windings shall be uniformly insulated and the low voltage neutral point shall be insulated for
full voltage.

16. IMPEDANCE VOLTAGE

The impedance shall be as follows:

10 MVA 8.0%
20MVA 10.0%

The impedance voltage refers to all tap positions i.e. the manufacturer should maintain the
following impedance with it’s given tolerance at any tap position of the transformer. No negative
tolerance on this percentage impedance is allowed. A positive tolerance of +10% is allowed.
Transformers of each rating shall have corresponding impedance per tap characteristics such that
transformers of the same rating can be operated in parallel and it should be provided along with the
routine test report.

17. SHORT CIRCUIT PERFORMANCE

The transformer shall be capable of withstanding the thermal and dynamic effects of short circuits,
as specified in IEC 76-5 ‘Ability to withstand short circuits’.

Each transformer shall be capable of withstanding for 2 seconds a bolted metallic short circuit on
the terminals of either winding with rated voltage on the other winding and the tap-changer in any
position.

Short circuit tests shall have been carried out on the particular design of transformer offered, the
test results shall be supplied with the bid.

18. REGULATION

The regulation of each transformer from no-load to continuous rated output at 1.0 power factor and
at 0.85 lagging power factor shall be as guaranteed in the Technical Data Schedules.

19. FLUX DENSITY

Each transformer shall be capable of operating continuously with rated current and with system
maximum voltage applied to the low voltage winding at a frequency of 96 per cent of rated
frequency without exceeding the temperature rise specified in Clause 12.

The limit of flux density at normal voltage and frequency shall be subject to the requirements for
losses, harmonics and noise suppression but in any event shall not exceed 1.6 Tesla.

The transformer core shall not be saturated at maximum system voltage i.e. 36 kV.

220
20. HARMONIC CURRENTS

The transformers shall be designed with particular attention to the suppression of harmonic
voltages, especially the 3rd, 5th and 7th harmonics, so as to eliminate wave form distortion and the
possibility of high frequency disturbances, induction effect or of circulating current between neutral
points at different transformer stations.

21. PARTIAL DISCHARGE

Each transformer shall be partial discharge free up to 120% of rated voltage as the voltage is
reduced from 150% of rated voltage i.e. there shall be no significant rise above background level.

22. VOLTAGE CONTROL

22.1 General

Transformers shall be provided with tap changers for varying the effective transformation ratio.
Control schemes shall utilize 110V ac centre tap earthed voltage derived from the LV 3-Phase, 4-
Wire system. Phase failure relays shall be provided to ensure a secure supply. Winding taps as
called for in the Technical Requirements and Guarantee Schedule shall be provided on the high
voltage winding.

All terminals shall be clearly and permanently marked with numbers corresponding to the cables
connected thereto.

Tap positions shall be numbered consecutively, ranging from one upwards. The tap positions shall
be numbered so that by raising the tap position the LV voltage is increased

22.2 On-Load Tap Changers

22.2.1 General

On-load tap changers are according as per IEC 60214 and be from Maschinenfabrik
Reinhausen(MR) Germany/ABB Sweden and should be of the vacuum switching
type in order to comply with existing equipment standards, including operational
experience, spare parts, interchangeability, system reliability etc.. The On-Load Tap
Changers shall be Oil/Vacuum type.

Current making and breaking switches associated with the tap selectors or otherwise
where combined with tap selectors shall be contained in a tank in which the head of oil is
maintained by means completely independent of that on the transformer itself. Details of
maintaining oil separation, oil levels, and detection of oil surges and provision of alarm
and trip contacts shall be dependent on the design of tap-changer and be to the approval of
the Project Manager.

22.2.2 Mechanisms
The tap change mechanism shall be designed such that when a tap change has been
initiated, it will be completed independently of the operation of the control relays and
switches. If a failure of the auxiliary supply during tap change or any other contingency
would result in that movement not being completed an approved means shall be provided
to safeguard the transformer and its auxiliary equipment.

221
 Limit switches shall be provided to prevent over-running of the tap changing mechanism.
These shall be directly connected in the operating motor circuit. In addition, mechanical
stops shall be fitted to prevent over-running of the mechanism under any conditions. For
on-load tap change equipment these stops shall withstand the full torque of the driving
mechanism without damage to the tap change equipment.

Thermal devices or other approved means shall be provided to protect the motor and
control circuit.

A permanently legible lubrication chart shall be provided and fitted inside the tap change
mechanism chamber.

22.2.3 Local and Remote Control

Equipment for local manual and electrical operation shall be provided in an indoor cubicle
complying with Section-2. A thermostat controlled anti-condensation heater is to be
provided in the cubicle. Electrical remote control equipment shall also be supplied as
specified.

The following operating conditions are to apply to the on-load tap changer controls:-

a) It must not be possible to operate the electric drive when the manual operating gear is
in use.
b) It must not be possible for two electric control points to be in operation at the same
time.
c) Operation from the local or remote control switch shall cause one tap movement only,
unless the control switch is returned to the off position between successive operations.
d) It must not be possible for any transformer operating in parallel with one or more
transformers in a group to be more than one tap out of step with the other transformers
in the group.
e) All electrical control switches and local manual operating gear shall be clearly labeled
in an approved manner to indicate the direction of tap changing, i.e. raise and lower
tap number.
f) Emergency stop push-button at local and remote control positions.

22.2.4 Indication

Apparatus of an approved type shall be provided on each transformer:

a) To give indication mechanically at the transformer and electrically at the remote

control point of the number of the tapping in use.
b) To give electrical indication, separate from that specified above, of tap position.
c) To give indication at the remote control point that a tap change is in progress; this
indication to continue until the tap change is completed.
d) To give indication at the remote control point when the transformers operating in
parallel are operation out of step.
e) To indicate at the tap change mechanism the number of operations completed by the
equipment.

222
22.4 Automatic Voltage Control
Automatic Voltage Controller shall be from ‘MR’ Germany/ABB Sweden which is suitable
for control of transformers in parallel. This relay should have the IEC 61850 protocol.

In addition to the methods of control included in this specification, the following methods
shall also be provided. This is for future addition of a similar transformer and associated
parallel operation.
a) Automatic Independent – It shall be possible to select automatic independent control
for each transformer irrespective of the method of control selected for any other of
the associated transformers.
b) Automatic parallel – It shall be possible to select any transformer for master or
follower control. It must not be possible to operate any tap changer by remote or
local electrical manual control while the equipment is switched for automatic
operation.

22.4.1 Voltage Regulating Relays

Automatic voltage control shall be initiated by a voltage regulating relay of an approved

type and suitable for flush mounting. The relay shall operate from the nominal reference
voltage stated in the Schedule of Requirements derived from a circuit mounted LV
voltage transformer having Class 1.0 accuracy to IEC 60186 and the relay voltage
reference balance point shall be adjustable.

The relay bandwidth shall preferably be adjustable to any value between 1.5 times and 2.5
times the transformer tap step percentage, the nominal setting being twice the transformer
tap step percentage.

The relay shall be insensitive to frequency variation between the limits of 47 Hz and 51
Hz. The relay shall be complete with a time delay element adjustable between 10 and 120
seconds. The relay shall also incorporate an under voltage blocking facility which renders
the control inoperative if the reference voltage falls below 80 percent of the nominal value
with automatic restoration of control when the reference voltage rises to 85 percent of
nominal value.

On each transformer the voltage transformer supply to the voltage regulating relay shall
be monitored for partial or complete failure. The specified indicating lamp and alarm will
be inoperative when the circuit- breaker controlling the lower voltage side of the
transformer is open and also that when the tap changer is on control other than automatic
control.
23. COOLING AND TEMPERATURE CONTROL

The banks of cooling radiators shall be detachable from the tank for transport and maintenance.
Shut-off valves shall be provided on the tanks of the transformers for this purpose. An air-vent and
draining plug shall be provided on each radiator bank. All external surfaces of the radiators shall be
hot dip galvanized as specified in Sub-clause 13.2, Part 1 of this document. Temperature control
equipment shall be housed in a local control box mounted on the side of the transformer. A 150mm
diameter dial thermometer shall be provided to indicate the temperature of the top oil in the
transformer. This thermometer shall be fitted in such a way that it can easily be read from ground
level through a window in the door of the control box. The thermometer shall be fitted with two

223
adjustable contacts, one connected to give an alarm and one to trip associated circuit breakers. It
shall also be fitted with a maximum temperature pointer which shall be re-settable by hand.

A similar dial thermometer shall be provided in the control box to indicate winding temperature.
This thermometer shall have two sets of adjustable contacts one connected to give an alarm and the
other to trip associated circuit breakers and a maximum temperature pointer which shall be re-
settable by hand. The minimum range of these contacts shall be 50 C to 100 C for alarm and 60 C
to 120 C for trip. The temperature control box shall be weatherproofed to IP55 of IEC 529 or IS
2147 equivalent.

23.1 Cooling Plant

23.1.1 General

Radiators and coolers shall be hot-dip galvanized, designed so that all painted surfaces
can be thoroughly cleaned and easily painted in situ with brush or spray gun. The design
shall also avoid pockets in which water can collect and shall be capable of withstanding
the pressure tests specified in the schedule of requirements for the transformer main tank.

The clearance between any oil or other pipe work and live parts shall be not less than the
minimum clearances stated in the Employer’s Requirements.

23.1.2 Radiators connected directly to Tank

Where built-on radiators are used, each radiator shall be connected to the main tank
through flanged valves. Plugs shall be fitted at the top of each radiator for air release and
at the bottom for draining.

A valve shall be provided on the tank at each point of connection to the tank.

23.1.3 Cooler Banks

Each cooler bank shall be provided with:-

A) A valve at each point of connection to the tank.

B) A valve at each point of connection of radiators
C) Loose blanking plates for blanking off the main oil connections.
D) A 50mm filter valve at the top of each cooler bank.
E) A 50mm drain valve at the lowest point of each interconnecting oil pipe.
F) A thermometer pocket, fitted with captive screw cap in the inlet and in the outlet oil pipes.
G) Air release and drain plugs on each radiator.

The omission of any, or the provision of alternative, arrangements to the above

requirements will not be accepted unless approved in writing by the Project Manager before
manufacture.

23.1.4 Forced Cooling

The type of forced cooling shall be as stated in the Schedule of Requirements.
Forced cooling equipment of transformers of similar rating and design shall be
completely interchangeable, one with the other, without modification on Site.

224
23.1.5 Oil Pipes and Flanges

All oil piping necessary for the connecting of each transformer to its conservator, cooler
banks etc. shall be supplied and erected under this Contract.

The oil piping shall be of approved material with machined flanged joints. Copper pipe
work is to comply with BS 61.

Dimensions of steel pipes shall be in accordance with BS 3600 and the drilling of all pipe
flanges shall with BS 4504.

An approved expansion piece shall be provided in each oil pipe connection between the
transformer and each oil cooler bank.

All necessary pipe supports, foundation bolts and other attachments are to be provided.

It shall be possible to drain any section of pipe work independently of the rest and drain
valves or plugs shall be provided as necessary to meet this requirement.

23.1.6 Air Blowers

Air blowers for forced air-cooling shall be of approved make and design and be suitable for
continuous operation out-of-doors. They shall also be capable of withstanding the stresses
imposed when brought up to speed by the direct application of full line voltage to the
motor.

To reduce noise to the practical minimum, motors shall be mounted independently from the
coolers, alternatively, an approved form of anti-vibration mounting shall be provided.

It shall be possible to remove the blower, complete with motor, without disturbing or
dismantling the cooler structure framework.

Blades shall be of material subject to approval.

Blower casings shall be made or galvanized steel of thickness not less than 2.6 mm (14
S.W.G.) and shall be suitably stiffened by angles or tees.

Galvanized wire guards with mesh not exceeding 12.5mm shall be provided to prevent
accidental contact with the blades. Guards shall also be provided over all moving parts.
Guards shall be designed such that blades and other moving parts cannot be touched by test
fingers to IEC 529.

23.1.7 Cooler Control

Where forced cooling using multiple small single-phase motors is employed, the motors in
each cooling bank shall be grouped so as to form a balanced three-phase load.

Each motor or group of motors shall be provided with a three-pole electrically operated
Contractor and with control gear of approved design for starting and stopping manually.

225
 Where forced cooling is used on transformers, provision shall be included under this
contract for automatic starting and stopping from contacts on the winding temperature
indicating devices as specified. The control equipment shall be provided with a short time
delay device to prevent the starting of more than one motor, or group of motors in the case
of multiple cooling, at a time.

Where motors are operated in groups, the group protection shall be arranged so that it will
operate satisfactorily in the event of a fault occurring in a single motor.

The control arrangements are to be designed to prevent the starting of motors totaling more
than15 KW simultaneously, either manually or automatically. Phase failure relays are to be
provided in the main cooler supply circuit.

All contacts and other parts which may require periodic renewal, adjustment or inspection
shall be readily accessible.

All wiring for the control gear accommodated in the marshalling kiosk, together with all
necessary cable boxes and terminations and all wiring between the marshalling kiosk and
the motors, shall be included in the contract .Each box shall have a hinged gasketed door
lockable by padlock. Solar gain can give rise to high temperature in a local control box.
Adequate ventilation shall be provided to ensure that all equipment contained therein shall
operate satisfactorily under these conditions.

A terminal block with 10% spare terminals shall be provided in each temperature control
box.

24. TANK AND ACCESSORIES

24.1 General

The transformer tank shall be skid mounted type. The transformer tank shall be designed so that the
complete transformer with oil and excluding conservator and radiators can be lifted and transported
without permanent deformation or oil leakage. The tank and cover including the stiffeners shall be
designed in such a manner as to leave no external pockets in which water can lodge, or internal
pockets where gas/air can collect. All fittings shall be designed so as to prevent entry of air or
leakage of oil from the tank. All pipes, shall be externally welded to the tank wall. The tank and
cover shall be of structural quality, weld-able high tensile steel with a minimum thickness of 3mm.
All welding shall be stress relieved. The requirement of post weld heat treatment of tank/ stress
relieving shall be based on recommendation of BS-5500.

The tank lid shall not be welded shut, but shall be secured by bolts and provided with suitable oil-
tight gasket. The tank is to withstand vacuum up to 500mm of mercury for 5 MVA, 10 MVA and
20 MVA transformers and any pressure of oil developed during operation conditions including
short circuits.

24.2 Surface Treatment

The transformer tank and accessories shall be adequately protected against corrosion. The inside of
the tank shall be painted with an approved oil resisting varnish. The outside of the tank shall be
painted as specified in Sub-clause 13.1, Part 1 of this document.

226
Conservator Tank:

A conservator tank shall be provided of adequate capacity between lowest and highest visible levels
to meet expansion of oil from 0 C to 100 C. A suitable oil level gauge shall be located on the tank
so that it can be easily read from ground level. The gauge shall be graduated for temperatures of 0
C, +45 C and +90 C.

Each gauge shall be provided with contacts for separate low oil level alarm and trip signals. The
conservator shall be fitted with a filling hole with cap and drain valve. It shall be inclined towards
the drain valve. The pipe connecting the conservator to the main tank shall project 20mm above the
bottom of the conservator for collection of impurities.

24.3 Breather

The conservator tank shall be fitted with a breather in which silica gel is the dehydrating agent from
any country of Europe, USA or Japan. The breather shall be a molded type transparent case of
adequate size and so designed that:

• the passage of air through the silica gel does not give rise to any excess pressure rise;
• silica gel crystal of not less than 5mm. size is used;
• the silica gel is sealed from the external atmosphere by means of an oil seal;
• the moisture absorption indicated by a change in color of the crystals can be easily observed
from a distance;
• the breather mounting height facilitates maintenance from ground level without switching out
the transformer.

24.4 Explosion Vent or Pressure Relief Device

An explosion vent or pressure relief device shall be provided to release any severe build-up of
pressure within the tank. The vent shall be designed such that in the event of an explosion, rain,
sand or any other foreign bodies are prevented from getting into the tank. The vent shall be
positioned so as to direct the explosion safely into the oil pit.

24.5 Oil Sampling Devices

Oil sampling devices shall be fitted to the main tank. They shall be located suitably for easy access
especially during maintenance, one near the bottom of the tank and one near the top.

24.6 Oil Filtration

Two 50mm bore filter valves shall be fitted to the tank, one on the top and the other diagonally
opposite on the bottom.

24.7 Lifting Lugs/Eyes

Lifting lugs shall be provided for supporting the weight of the transformer including core and
windings and fittings and with the tank filled with oil.

227
24.8 Jacking Pads

Four jacking pads shall be provided near the corners of the tank of each transformer and
approximately 400mm above the lowest part of the tank. These pads shall be designed to take the
complete weight of the transformer filled with oil.

24.9 Hauling Eyes

Hauling eyes shall be provided on all sides of the transformer.

24.10 Earthing Terminals

Earthing terminals shall be provided on the transformer close to each of the four corners of the tank
to facilitate easy earthing of the transformer on site.

24.11 Oil Valves

In addition to the valves already mentioned, a drain valve shall be provided near the bottom of the
tank. All oil valves shall be provided with means for securing them in the open or closed position.

25. TERMINAL BUSHING AND CONNECTIONS

25.1 General

Transformers are to be provided with outdoor type bushing insulators and cable box on the LV
side. HV and LV bushings shall be from Europe, USA or Japan origin.

All bushings shall comply with IEC 60137 and the minimum creepage distance for outdoor
bushings shall not be less than 25mm per kV of rated voltage between phases. Outdoor bushing
insulators shall be provided with adjustable arcing horns and for rated voltages of 36 kV and lower
these shall be of the duplex gap type.

Bushings shall be of sealed construction suitable for service under the very humid conditions at site
and, addition, for the very rapid cooling of equipment exposed to direct sunlight when this is
followed by sudden heavy rainstorms.

Typical sections of bushing insulators showing the internal construction, method of securing the top
cap and methods of sealing shall be included in the Bid.

Completely immersed bushings and lower voltage outdoor immersed bushings may be of other type
of construction, subject to the approval of the Project Manager but bushings of resin bonded paper
construction are not permitted. The 33 kV bushings shall be porcelain (solid or condenser type). On
all condenser bushings a tapping shall be brought out to a separate terminal for testing purposes on
Site.

Special precautions shall be taken to exclude moisture from any paper insulation during
manufacture, assembly, transport and erection. Terminal arrangement of LV cable box position &
neutral bushing position shall be as per approved drawings.

228
25.2 Porcelain

Hollow porcelain shall meet the test requirements of IEC 60233 and shall be sound, free from
defects and thoroughly vitrified. Designs based on jointed porcelains will not be acceptable. The
glaze must not be depended upon for insulation. The glaze shall be smooth, hard, of a uniform
shade of brown and shall cover completely all exposed parts of the insulator. Outdoor insulators
and fittings shall be unaffected by atmospheric conditions producing weathering, acids, alkalis, dust
and rapid changes in temperature that may be experienced under working conditions.

The porcelain must not engage directly with hard metal and, where necessary, gaskets shall be
interposed between the porcelain and the fittings. All porcelain clamping surfaces in contact with
gaskets shall be accurately ground and free from glaze.

All fixing material used shall be of suitable quality and properly applied and must not enter into
chemical action with the metal parts or cause fracture by expansion in service. Cement thickness
are to as small and even as possible and proper care is to be taken to center and locate the
individual parts correctly during cementing.
All porcelain insulators shall be designed to facilitate cleaning.

25.3 Marking

Each porcelain insulator shall have marked upon it the manufacturer’s name or identification mark
and year of manufacture. These marks shall be clearly legible after assemble of fittings and shall be
imprinted before firing, not impressed.

When a batch of insulators bearing a certain identification mark has been rejected, no further
insulators bearing this mark shall be submitted and the Contractor shall satisfy the Project Manager
that adequate steps will be taken to mark or segregate the insulators constituting the rejected batch
in such a way that there can be no possibility of the insulators being re-submitted for the test or
supplied for the use of the Employer.

Each complete bushing shall be marked with the manufacturer’s name or identification mark, year
of manufacture, serial number, electrical and mechanical characteristics in accordance with IEC
60137.
25.4 Mounting of Bushings
Bushing insulators shall be mounted on the tank in a manner such that the external connections can
be taken away clear of all obstacles. Neutral bushings shall be mounted in a position from which
connection can be taken to a neutral current transformer mounted on a bracket secured to the
transformer tank. The current transformer will be supplied by the switchgear manufacturer but
provision shall be made on the tank for mounting to theProject Manager’s requirements.
The clearances from phase to earth must not be less than those stated in the Technical
Requirements and Guarantee Schedule.

A flexible pull-through lead suitably suited to the end of the winding copper shall be provided for
the bushings and is to be continuous to the connector which is housed in the helmet of the bushings.
When bushings with an under-oil end of a re-entrant type are used the associated flexible pull-
through lead is to be fitted with suitably designed gas bubble deflector. The bushing flanges must
not be of re-entrant shape which may trap air.

Clamps and fittings made of steel or malleable iron shall be galvanized and all bolt threads are to be
greased before erection.

229
25.5 Tests

Routine, sample and type tests of Bushing shall be carried out in accordance with the specified
standards. Type tests shall also be carried out unless approved type test evidence is submitted.
These tests shall include temperature cycle and porosity tests.

The following standards shall apply:-

IEC 60233(BS 4963) for hollow porcelains.
IEC 60137 for bushings.
IEC 60148 and 60273 (BS 3297) for high voltage post insulators.
IEC 60383 and 60305 (BS 137 Part 1 and Part 2) for cap and pin string insulators.

26. CORE AND WINDINGS

26.1 General
The winding shall be of high-conductivity electrolytic copper and transposed winding conductors
shall be employed where applicable. Maximum current density for HV and LV windings should
not exceed 2.5 A/mm2.

The Windings shall have uniform insulation as defined in IEC 76. All neutral points shall be
grounded.

The windings shall be located in a manner which will ensure that they remain electro- magnetically
balanced and that their magnetic centers remain coincident under all conditions of operation.

The windings shall also be thoroughly dried and shrunk by the application of axial pressure for
such length of time as will ensure that further shrinkage will not occur in service.

The windings and leads of all transformers shall be braced to withstand the shocks which may
occur through rough handling and vibration during transport, switching and other transient service
conditions including external short circuit
26.2 Core
The core shall be constructed from high grade, non-ageing, cold rolled grain oriented silicon steel
laminations. The core and winding shall be capable of withstanding shocks during transport,
installation and service. Provision shall be made to prevent movement of the core and windings
relative to the tank during these conditions and also during short circuits.
The design shall avoid the presence of pockets which would prevent the complete emptying of the
tank through the drain valve.
26.3 Windings
The winding conductor shall be of electrolytic copper, free from burs and splinter. Paper shall be
used for conductor insulation. The insulation shall be free from insulating compounds which are
iliable to soften, ooze out, shrink or collapse. It shall be non catalytic and chemically inert in
transformer oil during normal service.
The stacks of windings are to receive adequate shrinkage treatment.
The windings and connections are to be braced to withstand shocks during transport, switching,
short circuit or other transient conditions. The manufacturer must provide the thermal damage
curve or thermal damage description of the transformer winding or the transformer as per relevant
IEC standard.
The winding shall be of electrolytic copper, free from burs and splinter. Paper shall be used for
conductor insulation.

230
27. INTERNAL EARTHING

27.1 General

All metal parts of the transformer, with the exception of the individual core laminations, core bolts
and associated individual clamping plates, shall be maintained fixed potential.

27.2 Earthing of Core clamping Structure

The top main core clamping structure shall be connected to the tank body by a copper strap. The
bottom main core clamping structure shall be earthed by one or more of the following methods:

a) by connection through vertical tie rods to the top structure;

b) by direct metal-to-metal contact with the tank base maintained by the weight of the core and
windings;
c) by connection to the top structure on the same side of the core as the main earth connection
to the tank.

27.3 Earthing of Magnetic Circuits

The magnetic circuit shall be earthed to the clamping structure at one point only through a
removable link placed in an accessible position just beneath an inspection opening in the tank
cover and which, by disconnection, will enable the insulation between the core and clamping
plates, etc., to be tested at voltages up to 2 kV. The link shall have no detachable components and
the connection to the link shall be on the same side of the core as the main earth connection. These
requirements are compulsory.

All insulating barriers within magnetic circuits shall be bridged by means of aluminum or tinned
copper strips, so inserted as to maintain electrical continuity.

27.4 Earthing of Coil Clamping Rings

Where coil clamping rings are of metal at earth potential, each ring shall be connected to the
adjacent core clamping structure on the same side of the transformer as the main earth connection.
27.5 Size of Earthing connections

Main earthing connections shall have a cross-sectional area of not less than 80 sq.mm but
connections inserted between laminations may have cross-sectional areas reduced to 20 sq. mm
when in close thermal contact with the core.

28. TANKS AND ANCILLARY EQUIPMENT

28.1 Transformer Tanks

Each transformer shall be enclosed in a suitably stiffened weld-able high tensile steel tank such
that the transformer can be lifted and transported without permanent deformation or oil leakage.
The construction shall employ weld-able structural high tensile steel of an approved grade to BS
7613 and BS EN10029. The final coat colour of Transformers shall be to Munsell notation N5Y-
7/l.
Lifting lugs shall be provided, suitable for the weight of the transformer, including core and
windings, fittings, and with the tank filled with oil. Each tank shall be provided with at least four
jacking lugs, and where required, with lugs suitably positioned for transport on a beam transporter.
Haulage lugs should also be provided to enable a cable to be used safely for haulage in any
direction.
231
The transformer tank shall be capable of withstanding vacuum up to 500 mm of mercury without
defection exceeding the value stated in the Schedule of Requirements.

Where the design of the tank is such that the bottom plates will be in direct contact with the surface
of the foundations. The base of each tank shall be so designed that it is possible to move the
complete transformer unit in any direction without injury when using rollers, plates, or rails

All joints, other than those which may have to be broken, shall be welded.

The tank and cover shall be designed in such a manner as to leave no external pockets in which
water can lodge, no internal pockets in which oil can remain when draining the tank or in which air
can be trapped when filling the tank, and to provide easy access to all external surfaces for
painting. Where cooling tubes are used, each tube shall be of heavy gauge steel welded into the
tank sides, top and bottom.

Each tank cover shall be of adequate strength, must not distort when lifted and shall be provided
with suitable f1anges having sufficient and properly spaced bolts. Inspection openings shall be
provided to give access to the internal connections of bushings, winding connections and earthing
links. Each opening shall be correctly located and must be of ample size for the purpose for which
it is intended. All inspection covers shall be provided with lifting handles.

It must be possible to remove any bushing without removing the tank cover.

Pockets shall be provided for a stem type them1ometer and for the bulbs of temperature indicators
where specified. These pockets shall be located in the position of maximum oil temperature and it
must be possible to remove any bulb without lowering the oil level in the tank. Captive screwed
caps shall be provided to prevent the ingress of water to the thermometer pockets when they are
not in use. Where called for in the Technical Requirements and Guarantee Schedule,
accommodation shall be provided for outdoor weatherproof neutral current transformer. A ladder
shall be provided on one side of the tank as a means for inspection and access to the top of the
transformer. The lower section of the ladder shall be equipped with a barrier complete with
provision for locking with a padlock.

232
28.2 Conservator Tanks, Breathers and Air Dryers

Each transformer shall be provided with an overhead conservator tank formed of substantial steel
plates and arranged above the highest point of the oil circulating system. Connections into the
main tank shall be at the highest point to prevent the trapping of air or gas under the main tank
cover. A steel ladder shall be fixed between conservator top and the transformer top cover.

The capacity of each conservator tank shall be adequate for the expansion and contraction of oil in
the whole system under the specified operating conditions. Conservator tanks shall also be
provided with a cleaning door, filling cap, drain valve with captive cap and an oil level indicator
with minimum and maximum levels indicated. The normal level at an oil temperature of 25°Cshall
be indicated and the minimum and maximum levels shall also be correlated with oil temperature
markings. The temperature markings shall preferably be integral with the level indicating device.
The Oil level indicator shall be from MR. Germany or equivalent European class.

The location of the conservator tank shall be so arranged that it does not obstruct the passage of
high voltage conductors immediately above the transformer.

The pipe work between the conservator and the transformer tank shall comply with the standard
requirements and a valve shall be provided at the conservator to cut-off the oil supply to the tank.

Each conservator shall be fitted with an air cell which shall be connected to a silica gel breather of
a type which permits the silica gel content to be removed for drying. Due to the climatic conditions
at site, this breather shall be larger than would be fitted for use in a temperate climate. All
breathers shall be mounted at a height of approximately 1400 mm above ground level. The silica
gel container shall be fully transparent.

28.3 Valves

Each transformer shall be fitted with the following valves as a minimum requirement:

28.3.1 Main Tank

a) One 50mm bore filter valve located near to the top of the tank.

b) One 50 mm bore filter valve located near to the bottom of the tank and diagonally
opposite to the filter valve required against(A).Where design permits, this valve may be
combined with item (C).

c) One 50mm drain valve with such arrangements as may be necessary inside the tank to
ensure that the tank can be completely drained of oil as far as practicable. This valve
shall also be provided with an approved oil sampling device.

d) One valve between the main tank and gas actuated relay, complete with bypass facility
to facilitate removal of relay and maintain oil flow.

233
28.3.2 Conservator

a) One valve between the conservator and gas actuated relay for the main tank and where
appropriate, for the tap change diverter switch tank complete with by pass for
Buchholz relay to facilitate maintenance of the relay.

b) One drain valve for oil conservator tank so arranged that the tank can be completely
drained of all oil.

28.3.3 Radiators and Cooler Banks

a) Valves at each point of connection to the tank.

The two valves 28.3.1 (d) and 28.3.2 (a) arrangement across the gas actuated relay are to be
connected with an oil pipe work bypass facility to facilitate removal of the relay, due to
failure etc, and still maintain the oil flow system between the conservator and main tank.
Blank flanges, plates or captive screw caps shall be fitted to all valves and pipe ends not
normally connected in service.

The omission of any, or the provision of alternative arrangements to the above

requirements, will not be accepted unless approved in writing by the Project Manager
before manufacture.

28.4 Joints and Gaskets

All joint faces shall be arranged to prevent the ingress of water or leakage of oil with a minimum
of gasket surface exposed to the action of oil or air.

Oil resisting synthetic rubber gaskets are not permissible except where the synthetic rubber is used
as a bonding medium for cork, or where metal inse1ts are provided to limit compression.

Gaskets shall have sufficient thickness consistent with the provision of a good seal and full details
of all gasket sealing arrangements shall be shown on the Plant drawings.
All gaskets shall be closed design (without open ends) and shall be one piece only. Exterior
gaskets shall be weatherproof and shall not be affected by strong sunlight. Care shall be taken to
secure uniformly distributed mechanical strength over the gaskets and retains throughout the total
length. No gaskets shall be used in which the material of the gasket is mounted on a textile
backing. Gaskets of neoprene or any kind of impregnated/ bonded core or cork only which can
easily damage by over pressing is not acceptable. Use of hemp as gasket material is also not
acceptable.

28.5 Pressure Relief device

An approved pressure relief device of sufficient size for the rapid release of over pressure that may
be generated in the tank, and designed to operate at a static pressure lower than the hydraulic test
pressure, shall be provided. It shall be of the spring operated valve type and shall be provided with
one set of normally open signaling contacts which will be used for trip alarm purposes. The
pressure relief device shall be from 'MR' or equivalent European made.

The relief device is to be mounted on the tank cover and is to be provided with a skirt to project
at least 25 mm in to the tank to prevent gas accumulation. Discharge of oil shall be directed away
from the transformer top cover and clear of any operating position.

234
28.6 Earthing Terminals

Two substantial steel flag type terminals having two 14mm diameter holes on 55mm
centers shall be located one on either side and near to the bottom of the transformer to
facilitate connection to the local earthing system.

28.7 Rating, Diagram and Valve Plates

The following plates, or an approved combined plate, shall be fixed to each transformer
tank at an average height of 1500 mm above the ground level:

a) A rating plate bearing the data specified in IEC 76 Part 1. This plate shall also include
the short-circuit current rating and time-factor for each winding.

b) A Diagram plate showing in an approved manner the internal connections and the
voltage vector relationship of the several windings, in accordance with IEC 76 Part1
with the transformer voltage ratio for each tap and, in addition a plan view of the
transformer giving the correct physical relationship of the terminals.

c) A plate showing the location and function of all valves and air release cocks or plugs.
This plate shall also if necessary warn operators to refer to the Maintenance Instructions
before applying vacuum.

Plates are to be of stainless steel or other approved material capable of withstanding the
rigorous of continuous outdoor service at site.

29. STATION AUXILIARY TRANSFORMER:

The Contractor shall supply Station Auxiliary transformer with 10 MVA & 20 MVA OLTC
Transformer.
Auxiliary transformers shall be hermetically sealed two-winding, conservator type, three-phase, oil
immersed, ONAN, with Off Load Tap Changing, suitable for outdoor use.

The station auxiliary transformers shall be 33/0.415 kV and have a maximum continuous rating of
100 kVA, shall be capable of supplying the maximum continuous rating for all tap positions and
maintaining rated voltage on the low voltage winding, under the maximum ambient temperature
conditions, without the temperature rise of the top oil exceeding 50°C or the temperature rise of the
windings as measured by resistance exceeding 55°C.

Transformers shall be in accordance with the relevant IEC standard and this specification. Refer to
the Schedule of Technical Particulars and Guarantees for other relevant requirements.

Off-load tap-changing shall be carried out by means of an external hand-operated tapping switch
mounted on the side of the tank. All phases of the tapping switch must be operated by one hand
wheel.

The tapping switch shall have a spring-loaded captive bolt or other approved means on the moving
part which positively locates the switch correctly at each tapping position. This bolt must be

235
lockable at each tapping position and shall be provided with a suitable padlock and keys. Moving
the switch from one tapping position to another shall require that the bolt be withdrawn by hand
from its locating socket on the transformer tank against the spring pressure.

Tap-position numbers corresponding to the tapping switch bolt-locating sockets shall be cast or
engraved in a metal indication plate fixed to the tank and a keyed metal pointer on the tapping
switch operating handle shall show clearly at which tapping number the transformer is operating.

All tap-position indicators shall be marked with one integer for each tap position, beginning at
number 1. Adjacent taps shall be numbered consecutively in such a manner that when moving a tap
to a new tapping position which has a higher number, the no-load output voltage of the untapped
winding increases.

29.1 Technical Requirements

Transformers shall be provided with the following fittings:
Off-load tap changer.
Oil filler plug and drain valve.
Thermometer.
Pressure release device.
Four lifting lugs.
Air insulated terminals for 33kV and 0.4 kV connections using adequately sized
conductor.
Galvanised tank, conservator and radiators.
30. CABLE TERMINATIONS AND GLANDS
30.1 Cable Boxes
The transformers may have cable boxes with all necessary fittings and attachments as per approval
of Drawings (submitted by the bidder) by the proper authority of BREB. Cable boxes shall be of
adequate proportions and designed in accordance with BS 6435 in such the manner that they can be
opened for inspection without disturbing the gland plate or incoming cable(s).Cable boxes shall be
designed for ease of access for jointing and connecting the cable. They shall be constructed to
minimize the danger of fragmentation; cast iron boxes shall not be used. The cable box shall be of
such a design as to prevent ingress of moisture. Where blind tapped holes have to be provided,
studs shall be used and not bolts or set screws.

All gaskets, unless otherwise approved, shall be in one continuous piece without joints. Gaskets
shall not be compressed before use. Provision shall be made for earthing the body of each cable
box. Removable blank gland plates and suitable type and size of cable glands shall be supplied and
fitted for termination of the cables.
Dehydrating breather and draining holes protected by 1 mm aperture mesh shall be incorporated at
the base of the box to avoid moisture condensation within cable box and ensure drainage of
condensation respectively. Cable boxes shall be provided with suitable means for clamping the
armor wires of the cables.
Gland plates for single core cable shall be made from non-ferrous metal. The Contractor shall
guarantee (test certificate shall be supplied to prove) that the air clearances and the creep age path
on the bushing connecting to the associated switchgear or transformers shall be such that the
completed installation shall withstand in air the impulse and power frequency voltages appropriate
to the plant.
The cable box clearances would meet the requirements for BS 6435 for partially insulated cable
boxes. An earthing terminal shall be provided in each sealing end chamber to which the
connections from the transformer winding can be earthed during cable testing. Cable boxes shall be
provided on 33kV/11kV sides suitable for air insulations terminations of XLPE Copper Conductor
cables of minimum sizes as mentioned below:
236
31. TEMPERATURE AND ALARM DEVICES

31.1 Temperature Indicating Devices and Alarms

The transformers shall be provided with approved devices of Kilhstrom for indicating the top oil
temperature and hottest spot winding temperatures. The devices shall have a dial type indicator
and, in addition, a pointer to register the highest temperature reached. Each winding temperature
device shall have four separate contacts fitted, two of which shall be used to control the two groups
of cooling plant motors (i.e. AF1 and AF2), one to give an alarm and one to trip the associated
circuit breakers. The Temperature indicating device shall be from MR Germany or equivalent
European class.

To simulate indication of the hottest spot temperature of the winding the device shall comprise a
current transformer associated with one phase only and a heating device designed to operate
continuously at 130 percent of transformer CMR current and for30 minutes at 150 percent of CMR
current, associated with a sensing bulb installed in an oil tight pocket in the transformer top oil.

The winding temperature indicators (WTI) shall be housed in the marshalling cubicle. The tripping
contacts of the winding temperature indicators shall be adjustable to close between 80°Cand 150°C
and to re-open when the temperature has fallen by not more than 10°C.

The alarm contacts and the contacts used to control the cooling plant motors on the above devices
shall be adjustable to close between 50° C and 100° C and to re-open when the temperature has
fallen by a desired amount between 10° C and l5° C.

All contacts shall be adjustable to a scale and must be accessible on removal of the relay cover.
Alarm and trip circuit contacts shall be suitable for making or breaking 150 VA between the limits
or 30 volts and 250 volts AC or DC and of making 500 VA between the limits of 110 and250V
DC. Cooler motor control contacts shall be suitable for operating the cooler Contractors direct or,
if necessary, through an interposing relay.
The temperature indicators in the marshalling kiosk shall be so designed that it is possible to move
the pointers by hand for the purpose of checking the operation of the contacts and associated
equipment. The working parts of the instrument shall be made visible by the provision of cut-away
dials and glass-fronted covers and all setting and error adjustment devices shall be easily
accessible.

Connections shall be brought from the device to terminal boards placed inside the marshalling
cubicle.
Terminals, links and a 63mm moving iron ammeter shall be provided in the marshalling kiosk for
each WTI for:
a) Checking the output of the current transformer.
b) Testing the current transformer and thermal image characteristics.
c) Disconnecting the bulb heaters from the current transformer secondary circuit to enable the
instrument to be used as an oil temperature indicator. Links shall be provided as shown on
the drawing enclosed with the offer.

31.2 Gas and Oil-Actuated Relays (Buchholz Relays)

Each transformer shall be fitted with gas and oil-actuated relay equipment having alarm contacts
which close on collection of gas or low oil level, and tripping contacts which close following oil
surge conditions. The Relay shall be from MR, Germany or equivalent European class.

237
Each gas and oil-actuated relay shall be provided with a test cock to take a flexible pipe connection
for checking the operation of the relay by inserting air in the relay. The floats of the Buchholz shall
be solid body. Each relay shall be fitted with UV protective covered glass window for indication of
gas volume.

To allow gas to be collected at ground level, a small bore pipe shall be connected to the gas release
cock of the gas and oil-actuated relay and brought down to appoint approximately1400 mm above
ground level, where it shall be terminated by a cock which shall have provision for locking to
prevent unauthorized operation.

The design of the relay mounting arrangements, the associated pipe work and the cooling plant
shall be such that multi operation of the relay will not take place under normal service conditions,
including starting or stopping of oil circulating pumps, whether by manual or automatic control
under all operating temperatures.

The pipe work shall be so arranged that all gas arising from the transformer will pass into the gas
and oil-actuated relay. The oil circuit through the relay must not form a delivery path in parallel
with any circulating oil pipe, nor is it to be fed into or connected through the pressure relief vent.
Sharp bends in the pipe work shall be avoided.

When a transformer is provided with two conservators, the gas and oil-actuated relays shall be
arranged as follows:

a) If the two conservators are connected to the transformer by a common oil pipe, one relay
shall be installed in the common pipe.

b) If the two conservators are piped separately to the transformer, two relays shall be installed,
one in each pipe connection.

The clearance between oil pipe work and live metal shall be not less than the minimum clearances
stated in the schedule of requirement.

32. TRANSFORMER OIL

Insulating oil shall comply with the requirements of IEC 60296. Insulating oil shall be provided by
the Contractor for all oil-filled apparatus and 10% excess shall be provided for topping up purposes
in sealed drums. The Contractor shall satisfy himself that suitable oil treatment facilities are
available at Site for his use. If the Contractor is unable to obtain written assurances to this effect he
shall provide such oil treatment facilities as required to meet the specification, at no additional cost.

238
The Contractor shall supply the first filling of all insulating oil required for the operation of the
Plant and, after treatment, a test shall be made in the Project Manager’s presence to prove that the
breakdown voltage is at least 60kV at 2.5mm electrode gap.

Transformer Oil
Application Insulating mineral oil for Transformer
Grade of oil Class-1
a) Physical Properties
Appearance Liquid and free from suspended matter or sediment
Density at 200C 0.895g/cm3 (maximum)
Flash point (Closed cup) 0
140 C (minimum)
Kinematics Viscosity at-150C 800 cst. (Maximum)
Kinematics Viscosity at-200C 40 cst. (Maximum)
Pour point -300C (maximum)
b) Electrical Properties
Dielectric Strength at 50 Hz (with 2.5
On new untreated oil, the break down voltage shall be at
mm standard gap and 40 mm standard
least >60KV.
depth)
Loss tangent/ Dielectric dissipation
factor at temp 90 C, stress 500V/ mm to
1000 v/ mm and frequency 40 Hz to 62 0.005 (maximum)
Hz.
c) Chemical Properties
Neutralization value 0.03mg KOH/g (maximum)
Neutralization value after oxidation 0.40mg KOH/g (maximum)
Total sludge after oxidation 0.10% weight (maximum)
PCB Content Free from PCB
Performance and testing of oil shall comply with the
d) Standards latest revision of the relevant standards BS 148; 1972 IEC
– 60296or latest revision there on.

33. SURGE ARRESTERS (Station Class):

Required numbers of 33 KV & 11 KV Station Class Surge Arresters shall be provided along with
each transformer. The transformers will have mounting facilities for required 33 KV & 11 KV
surge arresters.

Surge arresters shall be of the type employing non-linear metal oxide resistors without spark gaps.
The Contractor shall demonstrate by calculations that the surge arresters will adequately protect the
switchgear arrangement.
Surge arresters shall be housed in porcelain insulators designed to withstand extremes of the
environment described. The insulation shall have a minimum creepage distance of 25mm/kV rated
system phase to phase voltage. Porcelain shall comply with IEC 60233. The method of sealing
against the ingress of moisture shall be of a type well proven in service and the manufacturing
procedures shall include an effective leak test which can be demonstrated to the inspecting engineer
if required. The MCOV of the Arresters are given below. MCOV exceeding the given range will
not acceptable.

The detailed calculation for Surge arrester operation and performance should be provided during
implementation prior to supply of each Surge arrester.

239
Arrester according to Voltage class MCOV range (KV)

10 KV 8 kV – 10 kV
30 KV 22 kV– 27.5 kV

Good electrical contact shall be maintained between resistor blocks taking account of any thermal
expansion and contraction of the block or mechanical shock during transport and erection, by
installing a well proven clamping system.
Metal oxide arresters installed outdoors shall be able to dissipate, when new, twice the energy
generated in the resistor blocks when energized at their maximum continuous operating voltage
immediately having been subjected to the discharge duties specified in IEC 60099-4 and assuming
that the porcelain housing and the surrounding air is at least 5 degree centigrade higher than the
maximum ambient air temperature specified.

All surge arresters shall be fitted with a pressure relief diaphragm which shall prevent explosive
shattering of the porcelain housing in the event of an arrester failure and the arrester shall have been
tested according to the high and low current tests specified in IEC 60099-1. Arresters shall be
supplied complete for installation in an outdoor switchyard, including insulating bases and surge
counters, one per phase, and, if applicable, grading rings. The material used for terminals shall be
compatible with that of the conductors to which they are to be connected.
Each arrester shall be identified by a rating plate in accordance with the requirements of IEC
60099-4. In addition an identification mark shall be permanently inscribed on each separately
housed unit of a multi-unit arrester so that units can be replaced in the correct position in the event
of them being dismantled.

Each surge arrester should have surge counter. The Surge counters shall have an internal assembly
which is matched to the line discharge capability of the arrester and shall include a leakage current
meter with a bi-linear scale for ease of reading. Auxiliary contacts are to be provided to signal
remote indication of counter operation. The manufacturer should declare the maximum count
number/ life of each surge arrester.

Surge arrester shall have suitable earth terminal to connect surge counter with insulated cable.
33.1 Tests
Routine tests and type tests shall be carried out to the specified standards. Bidder shall submit type
and routine tests reports of surge arresters along with bid proposal.

The following routine tests shall be carried out on all arrester units in accordance with clause 8.1 of
IEC 60099-4.
Measurement of reference voltage
Residual voltage test
Partial discharge test
Housing leakage test
Current distribution test for multi-column arrester.

240
34. LOSSES AND EVALUTION OF LOSSES

An adjustment will be made for evaluation purposes (only) for distribution transformer losses as
given below:

No load losses6384 USD/kW/unit of each type

Load losses1915 USD/kW/unit of each type

Load losses will be at full load and 75 C

Guaranteed loss values must be supported by test reports from internationally recognized
independent testing laboratory. In case of difference between the loss value declared in the offer
and the loss value to be found in the test report, the higher loss value will be taken into account for
the purpose of loss evaluation.
The Purchaser reserves the right to make independent test of transformer losses, in which case
these values will be used as actual tested losses. Further tests carried out during manufacture or
during pre-shipment inspection may also be taken account of in determining the loss values.

The acceptance of transformers yielding component losses higher than the guaranteed values shall
be governed by- IEC60076 part1. For actual tested losses higher than guaranteed figures but within
acceptable tolerance limits, the bidder will be penalized as follows:

a. US $ 9576 per kilowatt of increased amount of no-load loss per transformer.

b. US $ 2873 per kilowatt of increased amount of load loss per transformer.

The above penalties will be subtracted from any funds due to the Bidder. Final payment will not be
made until tests are reviewed and approved by Purchaser.
34.1 LOSSES
Instructions to Bidders: The maximum acceptable losses at 75 deg. C and at rated voltage, full site
rated load at any tap shall be as stipulated in the following table. Bidder’s quoting for transformers
with losses exceeding the following figures i.e. the declared loss at any tap (max., min., or
principal) is higher than the following losses shall not be accepted.

Losses in kW
Transformer Rating No Load
ONAN Load Loss
Loss (Iron
(Copper Loss)
Loss)
10 MVA ≤10 ≤57
20 MVA ≤12 ≤80

NOTE 1:
The no-load offered losses of a transformer shall not exceed the independent laboratory testvalue
by more than 10 % and the total offered losses of a transformer shall not exceed the independent
laboratory test value by more than 6%. It is noted that no-load and full-load losses offered by the
supplier shall not exceed the losses specified by BREB (mentioned in the clause 34.1 in the
specification).

241
34.2 REJECTION

The Employer may reject any transformer or whole lot, if during testing the following is found:

(a) Load and/or no-load losses exceed the guaranteed value by 15%.
(b) Total losses exceed the guaranteed values by 10%.
(c) Impedance exceeds the guaranteed value by more than 10%.
(d) Transformer fails any test.

NOTE 2:
If the measured losses exceeds the offered component losses (No load loss and full load loss) more
than 15% or measured total loss exceeds more than 10% of the offered total losses and percentage
impedance exceeds +10% of the specified percentage impedance then the whole lot will be
rejected. If the measured losses are in within above tolerance with the offered losses but exceeds
the specified value (mentioned in the clause 34.1 in the specification) then whole lot will also be
rejected.

The Contractor shall supply the replacement transformer and the requirements stated in this section
shall apply to the replacement units.

35. FOR OLTC Type 20/28 MVA 33/11.55 KV (ONAN/ONAF) TRANSFORMER

a) 20/28 MVA ONAN/ONAF indoor/outdoor mounting, 3-phase, 50 Hz, Dyn1, uniform

insulation, 33 kV +4×1.5% and -12×1.5% (HV taps on-load operating), mineral oil
immersed, equipped with BCT. The supply of transformer will also include suitable
size of MS rail for placing of transformer on foundation.
b)
Nominal System Voltage between Phases kV 33 11
System Frequency Hz 50 50
Rated Voltage between Phase kV 33 11.55
Highest system voltage kV 36 12.2 kV
Lightning Impulse withstand kV 170 75 kV
50 Hz withstand, 1 minute kV 70 28
Symmetrical Short Circuit Current kA 25 25
(3sec.)

c) The three H.T. bushing shall be porcelain type being brown glazed. The BCT fitted in
the neck of each bushing shall be 15VA, 600/5A, Class: 5P20

d) The three L.T bushings, one for each phase and one bushing for the neutral may be of
capacitor type or porcelain type with outside glazed of brown porcelain. The BCT fitted
in the neck on each phase bushings shall be 20 VA. 1800/5 A, Class: 5P20 and that on
the neutral bushing shall be 20VA, 1800/5 A, Class: 5P20. In addition to that the ''b"
phase bushing of the LT side should have a BCT having ratio 1800/5A, 20VA, 5P20
(for WTI), in "a'' phase bushing of the LT side should have another BCT having ratio
1800/5A. 20 VA, accuracy class .2(Metering CT FS < 5) (for OLTC by auto voltage
regulating relay) and in neutral phase bushing should have another BCT having ratio
1800/5A, 20 VA, 5P20 (for Stand by Earth Fault)."
e) The winding shall be of electrolytic copper, free from burs and splinter. Paper shall be
used for conductor insulation. The manufacturer must provide the thermal damage
curve or thermal damage description of the transformer winding or the transformer as
per relevant IEC standard

242
f) The insulating oil shall meet all requirements as defined by NEMA standard/BS shall
be chemically stable, free from acidity and other corrosive ingredients and shall possess
high dielectric strength oil for first filling shall be shipped in non-returnable drums.
10% of the quantity required for a transformer is to be supplied in addition in respect of
each transformer due to usual losses during installation, centrifuging, etc.

g) The transformer tank shall be of welded construction, fabricated from high tensile steel
plate and shall be designed so that the tank is to withstand vacuum up to 500mm of
mercury for 10 MVA and 20 MVA transformers and any pressure of oil developed
during operation conditions including short circuits.

h) The transformer shall have air seal conventional type oil conservator tank (the oil
surface is completely isolated from the atmosphere by installing an oil resistant rubber
seal in the interior of the conservator) at the top divided in to two halves internally: one
part to be connected with transformer main tank through Buchholz Relay (with cocks
on both side) and the other part with OLTC tank through another gas Relay (with cock
either side). Both the halves will have oil level indicator (visual) with contacts for
indication "LOW OIL LEVEL" in the control panel.

i) Pressure Release Devices for both main tank and OLTC Tank shall be provided.

j) Silica Gel Breather with glass window shall be provided for both halves of the
conservator tank.

k) The on-load Tap Changer operating device shall be equipped with local (manual and
electrical) and remote electrical operating device with appropriate interlocking. The
OLTC motor shall be 3-phase 400 V operating type. The mechanical position indication
shall be there both at the tap changer as well as on the operating device.
Contacts/Arrangements shall be there for remote position indication (by lamp glowing)
of the tap. Appropriate glands for the entry of control cable shall be provided.

l) Sufficient cooling Fans (3-phase, 415V, 50 Hz) of adequate capacity shall be fitted on
the body of the transformer for cooling purpose to achieve the ONAF rating over the
average ambient temperature of 40 degree C. There shall be a control device in weather
proof housing fitted on the body of the transformer and equipped with control relay
operated by sensing device of oil temperature inside the transformer and operate
requisite no. of fans. Besides there shall be manual switching device of cooling fans.

m) The Radiators shall be in banks which can be fitted with or removed from the body of
transformer tank. Sufficient radiators shall be provided to achieve the ONAN rating at
average ambient temperature of 40 degree C. Each bank of radiator must have two stop
valve one of which should be fixed at the top and the other at the bottom.

n) Besides the main components of the transformer the other features and accessories to be
associated which are as follows:

i) Inspection hole with cover.

ii) Manhole.
iii) Name plate with complete diagrams and main specifications. iv)
Upper and lower oil valves, oil sampling valve and drain valve.
v) Ladder to climb up to top with barrier at the bottom.
vi) Thermometer for sensing oil and winding temperature and display.
vii) All HV (33 KV) terminals shall be provided with appropriate connecting clamps
to be connected with 500 MCM Copper wire or Copper Bar or Copper Hollow

243
 Pipe which must be capable to carry at least 800 amps current. The LV (11 KV)
terminals shall have also connecting clamps appropriate for being connected with
on 4×500 mm2 single core cables per phase. The neutral terminal shall have
connecting clamps to be connected with 2/0 HDBS wire.
viii) There shall be four wheels (flanged type) suitable for mounting on rails and to
carry the transformer as a whole.
ix) The transformer shall have at least two grounding terminals on its body.
All ferrous parts of the transformer shall be galvanized or painted with appropriate
paints of MUNSELL NO-5y 7/1 transformer with maximum shipping height (not
exceeding 11 feet) will be preferred.
o) One set of extra gaskets for each transformer is to be supplied with the transformer lot
without extra cost.
36. FOR OLTC TYPE 10/14 MVA 33/11.55 KV (ONAN/ONAF) TRANSFORMER

a) 10/14 MVA ONAN/ONAF indoor/outdoor mounting, 3-phase, 50 Hz, Dyn1, uniform

insulation, 33 kV +4×1.5% and -12×1.5% (HV taps on-load operating), mineral oil
immersed, equipped with BCT. The supply of transformer will also include suitable
size of MS rail for placing of transformer on foundation.
b)
Nominal System Voltage between Phases kV 33 11
System Frequency Hz 50 50
Rated Voltage between Phase kV 33 11.55
Highest system voltage kV 36 12.2 kV
Lightning Impulse withstand kV 170 75 kV
50 Hz withstand, 1 minute kV 70 28
Symmetrical Short Circuit Current kA 25 25
(3sec.)

c) The three HT bushing shall be porcelain type being brown glazed. The BCT fitted in
the neck of each bushing shall be 15VA, 400/5A (for 10 MVA) Class: 5P20.

d) The three L.T bushings, one for each phase and one bushing for the neutral may be of
capacitor type or porcelain type with outside glazed of brown porcelain. The BCT fitted
in the neck on each phase bushings shall be 20VA. 1200/5 A, Class: 5P20 and that on
the neutral bushing shall be 20 VA, 1200/5 A, Class: 5P20. In addition to that the ''b"
phase bushing of the LT side should have a BCT having ratio 1200/5A, 20VA, 5P20
(for WTI), in "a'' phase bushing of the LT side should have another BCT having ratio
1200/5A. 20 VA, accuracy class .2 (Metering CT FS < 5) (for OLTC by auto voltage
regulating relay) and in neutral phase bushing should have another BCT having ratio
1200/5A, 20 VA, 5P20 (for Stand by Earth Fault)."

e) The winding shall be of electrolytic copper, free from burs and splinter. Paper shall be
used for conductor insulation.
The manufacturer must provide the thermal damage curve or thermal damage
description of the transformer winding or the transformer as per relevant IEC standard
f) The insulating oil shall meet all requirements as defined by NEMA standard/BS shall
be chemically stable, free from acidity and other corrosive ingredients and shall possess
high dielectric strength oil for first filling shall be shipped in non-returnable drums.
10% of the quantity required for a transformer is to be supplied in addition in respect of
each transformer due to usual losses during installation, centrifuging, etc.

g) The transformer tank shall be of welded construction, fabricated from high tensile steel
plate and shall be designed to withstand 500 mm of mercury.

244
 h) The transformer shall have air seal conventional type oil conservator tank (the oil
surface is completely isolated from the atmosphere by installing an oil resistant rubber
seal in the interior of the conservator) at the top divided into two halves internally: one
part to be connected with transformer main tank through Buchholz Relay (with cocks
on both side) and the other part with OLTC tank through another gas Relay (with cock
either side). Both the halves will have oil level indicator (visual) with contacts for
indication "LOW OIL LEVEL" in the control panel.
i) Pressure Release Devices for both main tank and OLTC Tank shall be provided.
j) Silica Gel Breather with glass window shall be provided for both halves of the
conservator tank.
k) The on-load Tap Changer operating device shall be equipped with local (manual and
electrical) and remote electrical operating device with appropriate interlocking. The
OLTC motor shall be 3-phase 400 V operating type. The mechanical position indication
shall be there both at the tap changer as well as on the operating device.
Contacts/Arrangements shall be there for remote position indication (by lamp glowing)
of the tap. Appropriate glands for the entry of control cable shall be provided.
l) Sufficient cooling Fans (3-phase, 415V, 50 Hz) of adequate capacity shall be fitted on
the body of the transformer for cooling purpose to achieve the ONAF rating over the
average ambient temperature of 40 degree C. There shall be a control device in weather
proof housing fitted on the body of the transformer and equipped with control relay
operated by sensing device of oil temperature inside the transformer and operate
requisite no. of fans. Besides there shall be manual switching device of cooling fans.
m) The Radiators shall be in banks which can be fitted with or removed from the body of
transformer tank. Sufficient radiators shall be provided to achieve the ONAN rating at
average ambient temperature of 40 degree C. Each bank of radiator must have two stop
valve one of which should be fixed at the top and the other at the bottom.
n) Besides the main components of the transformer the other features and accessories to be
associated which are as follows:
i) Inspection hole with cover.
ii) Manhole.
iii) Name plate with complete diagrams and main specifications. iv)
Upper and lower oil valves, oil sampling valve and drain valve.
v) Ladder to climb up to top with barrier at the bottom.
vi) Thermometer for sensing oil and winding temperature and display.
vii) All HV (33 KV) terminals shall be provided with appropriate connecting clamps
to be connected with500 MCM Copper wire or Copper Bar or Copper Hollow
Pipe which must be capable to carry at least 600 amps current. . The LV (11 KV)
terminals shall have also connecting clamps appropriate for being connected with
on 2×500 mm2 single core cables per phase. The neutral terminal shall have
connecting clamps to be connected with 2/0 HDBS wire.
viii) There shall be four wheels (flanged type) suitable for mounting on rails and to
carry the transformer as a whole.
ix) The transformer shall have at least two grounding terminals on its body.
All ferrous parts of the transformer shall be galvanized or painted with appropriate
paints of MUNSELL NO-5y 7/1 transformer with maximum shipping height (not
exceeding 11 feet) will be preferred.
37. WARRANTY
The Contractor shall warrant that the transformers furnished have conformed to this
specification. The warranty shall state that if, within three (3) years from the date transformers
are delivered , a transformer is found to have defects in workmanship or material or fails in
service , the Contractor shall repair or replace such defective parts (and other parts damaged as
a result) within 15 days with free of charge .

245
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
For OLTC Type 33/11.55 kV 10/14MVA POWER TRANSFORMERS
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the
tender.

Description Unit 10/14 MVA Power Transformer

Tenderers Guaranteed Values

BREB Requirement

1.Manufacturer’s Name Required

2.Manufacturer’s Address Required
3. Applied Standard Required
4. Type Outdoor Oil immersed

5. (a)Rated Power MVA ONAN/ONAF10/14 MVA

Three Phase
(b) Overload Capability In accordance with IEC
603564
6. Number of Phase Three
7. Rated Voltage, Phase to Required
Phase
High Voltage winding KV 33
Low Voltage winding KV 11.55
8. Rated frequency Hz 50
9. Rated insulation level Required
a)Impulse withstand, full wave
High voltage winding KV 170
Low voltage winding KV 75
Neutral side Full insulation
(b) AC withstand voltage
High voltage winding KV 70
Low voltage winding KV 28
10. Vector Diagram (IEC76-4) Dyn1 Required
ONAN/ Required
11. Type of Cooling ONAF
12. On load Tap – changer
Required
MR Germany/ABB Sweden
with Oil/Vacuum Switches
Type Required
Rated Capacity In Amps Required
Rated tap KV 33
Tap range % - 18 to +6
Numbers of tap Taps 17
Tap step % 1.5
Location of tap Primary side
Rated short time current KA Required
Oil volume Litre Required
Duration of one step change Sec Required
Motor rating KW Required

13. Impedance voltage at 75o

C and at nominal ratio and 8% (with tolerance of
100% rated power at %
+10%)
principal tap (with tolerance
of +10%)

246
 Description Unit 10/14 MVA Power Transformer

Tenderers Guaranteed Values

BREB Requirement

14.Temperature rise at
rated power (Max. ambient Required
temperature: 40o C)
Oil by thermometer Deg. C. 55
Winding by resistance Deg. C. 60
measurement.
Winding hot spot temperature
on emergency overload not to Deg. C. 140
exceed
Maximum hot spot
temperature when loaded in Deg. C. 118
accordance with IEC 354
15. System symmetrical fault
level at terminal of
33 KV KA 31.5
11KV KA 31.5
Duration of symmetrical short
circuit current for which the Sec 2
transformer is to be designed
16. Transformer core: Type of
core, max. flux density At Tesla ≤1.6
nominalvoltage
17. Transformer bushings
(a) H.V. Bushing
Voltage class Required
Cantilever strength Required
Transformer bushing HV CT Required
- Currrent Ratio A 400/5
- Rated burden VA 20
- Accuracy Class 5P20
(b) L.V. Bushing
Voltage class Required
Cantilever strength Required
Transformer bushing HV CT Required
(c) Neutral Bushing
Voltage class Required
Cantilever strength Required
18. Conservator Required
19. Auxiliary circuit voltage V 415/240 AC
for fan, etc, 3phase – 4 wire
20. Control Voltage V 110 DC
21. Sound level (IEC 60551)
ONAN dB Required
ONAF dB <80
22. Transformer Bushing CT
HV Side
On phase “a, b & c”
(Differential)
- Current Ratio A 400/5
- Rated burden VA 20
- Accuracy 5p20
- Short time current Required
LV Side
On phase “a, b & c”
- (Differential)
Current Ratio A 1200/5

247
 Description Unit 10/14 MVA Power Transformer

Tenderers Guaranteed Values

BREB Requirement

- Rated burden VA 20
- Accuracy 5p20
- Short time current Required
On phase “a” (OLTC)
- Current Ratio A 1200/5
- Rated burden VA 20
- Accuracy Class 5P20
- Short time current kA Required
On phase “b” (WTI)
- Current Ratio A 1200/5
- Rated burden VA 20
- Accuracy Class 5P20
- Short time current kA Required
Neutral Bushing CT for REF :
- Current Ratio A 1200/5
- Rated burden VA 20
- Accuracy Class 5P20
Neutral Bushing CT for stand
by earth fault
- Current Ratio A 1200/5
- Rated burden VA 20
- Accuracy Class 5P20
- Short time current KA Required
23. Number of Cooling fan Nos. Required
(main + spare)

Kw
24. Rating of Fan motors Required
(Maxm. 0.5
KW for Each)
25. Cooling fan losses at full
Kw Required+2
ONAN/ONAF capacity
operation
26. Core Loss at rated
Required
frequency and rated voltage Kw
at nominal tap.
27. Copper Loss at full load, at Required
rated frequency and at 75o C
(i)At ONAN
(a) At Maximum Tap Kw Required
(b) At Nominal Tap Kw Required
(c) At Minimum Tap Kw Required
(ii)At ONAF
(a) At Maximum Tap Kw Required
(b) At Nominal Tap Kw Required
(c) At Minimum Tap Kw Required
28. Exciting Current at A Required
nominal tap and rated voltage.
29. Dimensions and Weight Required
Maximum size for transport L mm Required
xWxH
Heaviest weight for transport Kg Required
Overall height mm Required
Oil volume Litre Required
Weight of oil Kg Required
Weight of core Kg Required
Total weight Kg Required

248
 Description Unit 10/14 MVA Power Transformer

Tenderers Guaranteed Values

BREB Requirement

30. Oil level indicator

Type & model Required
31. Pressure Relief Device
Type & model Required
32. Buchholz Relay
Type & model Required
Float Type
Petcock is provided for testing
Yes
by injecting air
Pipe arrangement for gas
release and oil collection from Yes
ground level
Oil surge protection Yes
Oil drain screw provided Yes
33. Oil & Winding
temperature indicator
Type & model Required
34. Efficiency at 750 C & unity
power factor
a) At 28 MVA load % -
b) At 20 MVA load % -
c) At 14 MVA load % Shall be Provided
d) At 10 MVA load % Shall be Provided
Shall be Shall be high tensile steel
35. Transtormer Tank
provided plate
36. Pressure release device for Shall be
Shall be provided
both main and OLTC Tank provided
37. Winding shall be of Shall be
Shall be electrolytic copper
electrolytic copper. provided
38. Pressure release device,
Temperature indicationg shall be from MR Germany
Shall be
device and Buchholz relay or Equivalent European
provided
shall be from MR Germany or Origin.
Equivalent European Origin.
39. Manual Shall be Provided

249
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 33 KV SURGE ARRESTER, STATION CLASS
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the
tender.

Tenderers
Sl REB
Description Unit Guaranteed
No Requirement
Values
33 KV SURGE ARRESTER
1. Manufacturer’s Name & Address Required
2. Class of diverter to IEC 99-4 Heavy duty, ZnO
3. Rated voltage (RMS) KV 30
4. Rated current KA 10
5. Neutral connection Effectively
earthed
6. Power frequency withstand voltage of housing:
Dry : KV 70 (RMS)
Impulse: KV 170
7. Lighting impulse residual voltage KV 100 peak
8. Steep current impulse residual voltage at 10 kA KV 110
or 1 S front time
9. Pressure relief device fitted? Y/N Required
10. Leakage current at rated voltage A Required
11. Minimum reset voltage V Required
12. MCOV KV 22 -27.5
13. Total creepage distance mm Required
14. Surge monitor Required
15. Connecting Lead from LA terminal to surge Shall be Insulated
2

monitor: 16 mm2
copper cable
16. Overall dimension and Weight :
Height mm Required
Diameter mm Required
Total weight of arrester Kg. Required
Height mm Required

250
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 11 KV SURGE ARRESTER, STATION CLASS
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the
tender.

Tenderers
SI REB
Description Unit Guaranteed
No Requirement
Values
11 KV SURGE ARRESTER
1. Manufacturer’s Name & Address Required
2. Class of diverter to IEC 99-4 Heavy duty, ZnO
3. Rated voltage (RMS) kV 10
4. Rated current kA 10
5. Neutral connection Effectively earthed
6. Power frequency withstand voltage of housing: Required
Dry : KV 28(RMS)
Impulse: KV 70
7. Lighting impulse residual voltage KV Required
8. Steep current impulse residual voltage at 10 kA
KV Required
or 1 S front time
9. Pressure relief device fitted? Y/N Required
10. Leakage current at rated voltage A Required
11. Minimum reset voltage V Required
12. Total creepage distance mm Required
13. MCOV KV 8.0 -10.0
14. Surge monitor To be provided
15. Connecting Lead from LA terminal to surge Shall 2be Insulated 16
monitor: mm copper cable
16. Overall dimension and Weight :
Height mm Required
Diameter mm Required
Total weight of arrester Kg. Required
Height mm Required

251
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 33/0.415 KV, 3 PHASE 200 KVA STATION TRANSFORMER
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the
tender.

REB Tenderers
Description Unit
Requirement Guaranteed Values
STATION SERVICE TRANSFORMERS
1. Manufacturer’s Name Required
2. Manufacturer’s Address Required
3. Type Required
4. Applicable Standard Required
5. Rated power KVA 200
6. Rated voltage :
- High voltage winding KV 33
- Low voltage winding at nominal tap – no load V 415/ 240
7. Vector diagram Dyn11
8. Rated Frequency Hz 50
9. Type of cooling ONAN
10. Type of bushing :
-High voltage Required
-Low voltage Required
11. Off load tap-changer :
-Rated tap KV 33
-Tap range % + 5 to – 5
- Number of taps Taps 5
12. Impedance voltage at 75deg C., at % 4%
nominal ratio and rated power
Temperature rise at rated power Required
(Max. ambient temp.: 40° C) Required
13. - Oil by thermometer Deg. C 60
14. Winding by resistance measurement Deg. C 65
15. Dimensions and Total Weight Required
16. Height x width x depth mm Required
17. Total weight Kg Required
18. Dimensions and Total Weight Required
19. No Load Loss Kw Required
20. Full Load Loss at 75° C Kw Required

252
 PUBLICATION NO: 1001-1999
RURAL ELECTRIFICATION BOARD (REB)
PEOPLESREPUBLIC OF BANGLADESH
STANDARD FOR

TECHNICAL SPECIFICATION FOR 33 KV OUTDOOR TYPE

VACUUM CIRCUIT BREAKER WITH CONTROL PANEL

1. SCOPE:

1.1 This Specifications intended to cover the design, manufacture, assembly and Testing at
manufacturer’s works of 33 KV, 3 Ph, 50 Hz, 2000/1250A, 31.5 KA 3s, Outdoor Type
Porcelain Clad, Vacuum Circuit Breaker for efficient and trouble-free operation as
specified hereunder.

1.2 The Circuit Breakers are required complete with structures, operating mechanism and all
associated accessories and auxiliaries.

2. STANDARDS:

The Equipment to be furnished under this Specification, shall be designed, constructed and tested in
accordance with the latest revisions of relevant International Electric-Technical Commission (IEC
56/IEC-62271-100). The Equipment conforming to any other national Technical standards which
ensure equivalent quality are acceptable.

Instructions to Bidders: In such cases the Bidders shall clearly indicate the standard adopted and
should furnish a copy of the English translation of the standard along with the bid.

International Electric-Technical Commission Standards of 60044-1 for CT and 60044-2 for PT and
Insulators and other devices, accessories etc. shall be followed relevant IEC standard.

3. GENERAL INFORMATION:

3.1 The Circuit Breakers specified herein are to be normally installed anywhere in Bangladesh
at an altitude not exceeding 1000 meters above mean sea level. For higher altitude beyond
1000 meters adequate creep age distance, pole to pole distance etc. shall be designed and
offered.

3.2 The general Weather Conditions are stated below.

i) Climate condition : The area is Tropical with monsoon from June to
October, about 3000 mm annual rain fall.
ii) Number of Thunderstorm days : 80 days/year.
iii) Ambient Temp : 450 C (max) and 40 C
iv) Maximum Wind Pressure (min). : 150 Kg. Mtr. Sq.

3.3 The Equipment offered shall be suitable for heavily polluted atmosphere.
3.4 The Equipment to be furnished under this Specification shall be packed for shipment so as
to meet the weight and space limitations of transport facilities, specifically along with Rail,
Road, right of way.

253
3.5 The Equipment covered by this Specification shall be complete in all respects. Any material
or accessory which may not have been specifically mentioned, but is essential or necessary
for satisfactory and trouble free operation and maintenance of the Equipment shall be
furnished without any extra charge to the Employer.
3.6 The Equipment shall be supplied with all accessories listed in this Specification with such
modifications and alternations as to safeguard the Technical requirements.

4. DESIGN CRITERIA:

4.1 The Equipment will be used in effectively neutral grounded System with fault level of 31.5
KA at highest system voltage of 36 KV.

4.2 Continuous current rating shall be 1250 Amp. Maximum temperature attained by any part
of the Equipment at specified rating should not exceed the permissible limit as stipulate in
the relevant standards. Equipment shall be designed taking 500C as maximum ambient
temperature.
4.3 The circuit breakers and their components shall be capable of withstanding the mechanical
forces and thermal stresses of the short circuit current of the system without any damage or
deterioration of material.

4.4 The circuit breakers shall have motor wound spring charged trip free mechanism with anti-
pumping feature, and shunt trip. In addition, facility for manual charging of spring shall be
provided.

4.5 Each breaker shall be provided with manual close & open facility, mechanical ON-OFF
indication, an operation counter and mechanism charge/discharge indicator.

4.6 For motor wound mechanism, spring charging shall take place automatically after each
breaker closing operation. One open-close-open operation of the circuit breaker shall be
possible after failure of power supply to the motor. A visual mechanical indicating device
will also be provided to show the position of the spring.

4.7 All controls shall be suitable for 80%, to 110% for closing & 70% to 110% for tripping of
110V D.C. The A.C. supply shall be available 415/230 Volt, 50 Hz.

4.8 The operating duty of the Breaker will be 0-0.3 sec-CO-3 min-CO.

4.9 There shall be no radio interference when the Equipment is operated up to maximum
service voltage.

4.10 The minimum safe clearance of all live parts of the Equipment shall be as per relevant
standards. Clearances of 33 KV Low Level pipe bus of switchyard are:

a) Phase to Phase : 1200 mm and :

b) Pipe bus to ground level of supporting structure 4000 mm

4.11 All electrical and mechanical interlocks which are necessary for safe and satisfactory
operation of the Breaker shall be furnished. The interlocking device shall be of proven
quality.

254
4.12 The condition of Breaker and its contacts shall be intact even under conditions of phase
opposition that may arise due to faulty synchronization or otherwise. Bidders should
confirm in this regards.

4.13 The Breaker shall be capable of smooth and rapid interruption of current under all
conditions, completely suppressing the undesirable phenomenon even under the most severe
and persistent rated short circuit conditions. There will be no abnormal voltage rise
subsequent to the switching ON/OFF a capacitor bank within the rated capacity.

4.14 The total make and break time (in m sec/cycle) for the breaker throughout the range of their
operating duty shall be indicated and guaranteed.

4.15 The breaker shall be suitable for interrupting low inductive currents without generation of
abnormal over voltage.

4.16 The breaker shall be capable of interrupting rated breaking current with recovery voltage
equal to maximum line Service Voltage and at all inductive power factor of the Circuit
equal to or exceeding 0.15.

4.17 The Circuit Breaker shall be capable to withstand power frequency over Voltage 70 KV for
1 min.

4.18 Instructions to Bidders: The Bidder may indicate in his offer the methods adopted for
limiting over voltage.
4.19 The Circuit Breaker with its hot dip galvanized steel structure shall be suitable for mounting
on concrete foundation. The height of the supporting structure will be such that it will be
able to maintain clearance as indicated in clause 4.10 above.

4.20 The detail of steel structure, foundation design and erection drawing shall be given. In
GA/Structure drawing please indicate the location of CB point of application of dynamic
load and its amplitude, dead load etc.

4.21 Special tools & tackles required for erection and dismantling and fitting of the Breaker and
its accessories, if required shall be offered indicating the prices etc.

5. CONSTRUCTION:

Each vacuum Circuit breaker shall comprise of three identical poles linked together electrically and
mechanically for synchronous operation.

Vacuum Interrupter

The vacuum interrupter, consisting of fixed contact and moving contact, shall be interchangeable
among the same type interrupter. Short circuit capacity of vacuum bottle should be 31.5 KA and
design life should be 100 nos. Operation at rated short circuit level. The operation of the interrupter
will be 30000 nos. at rated current.

i) Instructions to Bidders: Constructional features of the vacuum chamber along with its
functional arrangements are to be shown in a drawing submitted along with bid documents.

255
ii) The gap between contacts of the Circuit Breaker inside interrupter should be capable of
withstanding 1.3 time voltage to neutral at one atmospheric pressure at normal ambient
condition within Breaker in the event of vacuum pressure drop due to leakage.

iii) Vacuum Bottle shall be of Siemens/ABB or/ALSTOM and of reputed indigenous make.
Offered bottle shall be identical with Type tested one. Brochures/leaflet on technical data sheet
for vacuum bottle shall be enclosed with technical bid.

Control Panel and Protective Relays

i) Protective relays must be provided by the Contractor with the breaker. The relays must be
numerical relays (from ABB, Sweden or Siemens, Germany or GE, USA) for over current,
earth fault protection and differential of 33 kV feeder. There must be one master trip relay for
inter tripping.
ii) All the relays should be 61850 protocol type for automation network of the 33/11.55 kV Sub-
station.
iii) Plug setting range will be from 5% to 2500% and time setting range from 2.5% to 1000%.
iv) All indicating instruments shall be switch board type connected suitable for flush mounting and
provided with dust and vermin proof cases for tropical use and finished in suitable color. All
instrument have practical lab. means of adjustment of accuracy. The limit error of voltmeter and
ammeter shall be permissible for 0.2 instrument
v) There must have minimum 3 nos. Ammeter, 3 nos.voltmeter,1nos KW meter,1nos KVAR
meter, 1nos Pf meter, 1 nos. frequency meter 1 no. ammeter selector switch, 1 no. voltmeter
selector switch, Test terminal block, ON/OFF/Auto Trip/Spring Charge etc. indication lamps of
different colors. All indication meters will be Digital.

6.1 MAIN CONTACTS:

a) In vacuum interrupter the contact configuration, contact area, contact pressure will be
sufficient for carrying rated current and short time rates current, without any abnormal
phenomena.

b) Complete details of main contacts shall be furnished. The material of contacts and
coating of the contacts shall be suitable for vacuum Breaker technology. Evaporation of
metal during arcing and deposition of the same in the inner surface of vacuum
interrupter should be restricted by adopting suitable material. Bidder shall furnish the
justification of using the materials for contacts.

c) Complete details of main contacts and arc quenching device, if any with sectional
drawings shall be furnished at the time of offer. Measures taken to free the contacts
from vibration during closing shall be clearly explained in the drawing, support by tests
results.

d) The contact erosion should be limited up to 3 mm for useful life and indication to
monitor the progress of contact erosion has to be provided.

6.2 The vacuum pressure within interrupter shall be adequate to interrupt the fault current.
Precaution shall be taken so that there will be no flush over on outside of the vacuum
interrupter inside the porcelain insulator.
6.3 Design of the vacuum bottle and its insulator encasing should be suitable for outdoor use,
taking care of required creepage distance considering possibility of moisture condensation if

256
 any, in the annular space between the vacuum bottle and insulator enclosure. Type test with
identical bottle type with similar encasing arrangement shall be done and accordingly
Report shall be submitted along with bid document.

6.4 Vacuum bottle with its insulator encasing chamber shall be hermetically sealed. Free
passage of air in the chamber with or without provision of circulation of hot air is not
accepted.

6.5 Tripping/Closing Coil burden of Equipment should not be more than 200 watts at 110 V
D.C. The value will not be relaxed, specially for tripping coil.

6.5 OPERATING MECHANISM:

a) The operating mechanism shall be suitable for rapid closing and tripping. The opening
and closing energy shall be obtained from spring charge mechanism. The spring
charging may be done by either motor operation with facility for manual charging when
required or by other suitable trouble free mechanism. Local arrangement for operating
breakers both electrically and mechanically shall be provided in addition to remote
operation.

b) The mechanism shall have anti-pumping circuitry and will be trip free electrically and
mechanically. The anti-pumping arrangement shall be initiated through normally „NO‟
type, direct auxiliary contact of circuit breaker and shall be of self hold type. Plug-in
type relay/Contactor for Anti-pumping Relay will not be acceptable.

c) Spring operated mechanism will be complete with opening spring, closing spring, limit
switch and all necessary accessories to make the mechanism a complete operating unit.

d) Contactor used for anti-pumping relay shall be of reputed make.

e) There shall be mechanical ON/OFF indicator spring charge and operation counter for
each Breaker and also provision for remote indication.

f) The operating mechanism box shall be fixed at a working height from ground level.
View glass shall be provided on hinged door at the front side.

g) Spring charging LS shall have sufficient no. of spare contact.

6.6 COMMON CONTROL CUBICLE:

a) A free standing outdoor type weather proof, dust and vermin proof cubicle shall be
provided to house the operating mechanism and all other accessories except those which
must be located in the pole box.

b) The cubicle shall be of 3.00 mm thick sheet steel and shall have hinged doors at front
and hinged/bolted door or cover at rear for access to the mechanism. Doors should be of
proper design for smooth opening and closing with pad locking arrangement.

c) A removable gland plate of 3 mm thickness shall be provided at the bottom of the

cubicles for the Employer’s Cable entry. Glands of sizes suitable for entry of 1 no. 12
core, 2 nos. 8 core and 2 nos. 4 core Cables for Control etc.

257
 d) Terminal blocks for AC & DC shall be kept separate. Terminals shall be suitable for at
least 2X 2.5 sq.mm copper leads. All wiring shall be of 1100 V grade PVC.

e) Thermostat controlled heaters shall be provided to prevent condensation within cubicle.

Cubicle illumination Lamp with switch and a 230 V., 15A, 3 pin sockets with a Control
Switch shall be provided.

f) All controls, alarms, indications and interlocking devices furnished with breaker shall be
wired up to the terminal Black in the common control cubicle. Not more than two wires
shall be connected to one terminal.

g) All wires shall be identified at both ends with ferrule marking in accordance with
approved wiring diagram.

h) Terminal blocks shall have compression type multi-way terminals with bonding screws
and washers. At least 15% spare terminal shall be provided.

i) Scheme diagram on a durable sticker shall be fixed on inside door of Control Cubicle.

j) Degree of protection of control cubicle shall be IP-55.

7. INSULATORS:

a) Porcelain supports, interrupter housing of adequate mechanical and dielectric strength with
suitable creep age distance shall have to be used. All Support/Interrupter Housing of
identical ratings shall be interchangeable. Each Interrupter-Housing shall be provided with
terminal stud/pad.

b) The porcelain used in interrupter housing shall be made from wet process and shall be
homogeneous, free from laminations, caustics and other flaws which may impair its
mechanical or dielectric strength and shall be glossy, tough and impervious to moisture.

c) The porcelain supports, interrupter –housing insulation shall be coordinated with that of
Circuit Breaker. The puncture strength of the bushings shall be greater than the dry
flashover value.

d) When operating at rated voltage, there shall not be any electrical discharge between live
terminal and earth. No Radio disturbance shall be caused by the support insulators when
operating up to the maximum System Voltage. It shall also be free from corona.

e) All iron parts shall be hot dip galvanized. The nuts, bolts, washers etc. shall also be hot
dip galvanized steel or stainless steel.

f) Each Circuit Breaker shall be provided with Bi-metallic terminal stud/pad suitable for
connection of pipe bus/ACSR Conductor.

8. AUXILIARY CONTACTS:

a) Breaker shall be provided with 9 NO & 9 NC spare auxiliary contacts in addition to the
auxiliary contacts required for Breaker’s own operational requirements. These auxiliary
contacts shall preferably be convertible type.

258
 b) These contacts shall have continuous current rating of at least 10A. The breaking
capacity shall be adequate for the circuits controlled, or at least 12A at 110 V DC with a
circuit time constant of minimum 20 ms.

c) All these contacts shall be wired up to terminal block in the control cubicle. Auxiliary
contacts which are to be installed on the frame of Circuit Breaker shall be suitably
protected against accidental arcing from main circuit. Insulating materials of contacts
shall be ceramics or other non-tracking materials.

9. GROUNDING:

Circuit Breaker shall be provided with two grounding pads with 2 nos. tapped holes for M10 bolts
and spring washers for connection of the Employer’s grounding conductor (50x6 mm G.I. strips).

10. PAINTING:

External surfaces shall be given a coat of high quality red oxide or other suitable primer and shall
be finished with two coats of synthetic enamel paints. Such painting should be able to withstand
tropical climate as stipulated in Sl.No.3 of this Specification.

11. EQUIPMENT FOUNDATION AND STEEL STRUCTURE:

a) The Circuit breaker etc. shall be furnished complete with base frame, anchor/foundation
bolts and hardware. Details structure assembly drawing, mentioning part no. of each
member and also indicating cross sectional area of member used with supporting
calculations. The point of C.B. dynamic load and its amplitude, dead load etc. shall be
mentioned.
b) Similar grounding pad as mentioned against Sl.No.8 are also to be provided.

c) If the Centre line of Control Cubicle is more than 1.50m above ground plate, one
suitable platform with checker plate shall be fixed at a suitable height of support structure
with ladder step arrangement, to access the control cubicle for Local operation &
maintenance purpose.

12. CURRENT TRANSFORMER:

Current transformers, three per circuit breaker, shall be of outdoor, single phase, electromagnetic
induction, oil immerged, suitable for operation in hot and humid atmospheric conditions described
in service condition. They shall be mounted on the bracket. The CT tank should be Hot Dip
galvanized as per relevant IEC to prevent corrosion of all exposed metal parts.
12.1 Core

High grade non-ageing cold rolled grain oriented (CRGO M4 or better grade) silicon steel
of low hysteresis loss and permeability shall be used for the core so as to ensure specified
accuracy at both normal and over currents. The flux density shall be limited to ensure that
there is no saturation during normal service.

259
The instrument security factor of the core shall be low enough so as not to cause damage to the
instruments in the event of maximum short circuit current.

12.2 Winding

The secondary windings shall be made of electrolytic copper with suitable insulation. The
conductor shall be of adequate cross-section so as to limit the temperature rise even during
short circuit conditions. The insulation of windings and connections shall be free from
composition liable to soften coze, shrink or collapse during service.

Polarity shall be indelibly marked on each current transformer and at the lead and
termination at associated terminal blocks. CTs with multi ratio winding shall be clearly
tabulated to show the connections required for different ration. Similar numbers shall be
marked on terminal block arrangement and wiring diagram.

The continuous current rating of the primary winding shall be one hundred and twenty
percent of the normal rated current. Secondary windings of current transformers shall be
used for metering, instrumentation and protection and shall be rated for continuous current
of one hundred and fifty percent of normal rated current of primary winding.

12.3 Construction

The current transformer enclosures shall be made of high quality steel and shall be not dip
galvanized and shall be able to withstand and stresses occurring during transportation and
the terminal and mechanical stresses resulting from maximum short circuit current in
service. The primary winding and terminals shall be in a tank and supported by a hollow
porcelain insulator. The secondary connection shall be conducted through the hollow
insulator and terminated in a terminal box mounted on the base plate.

12.4 Insulation level

The current transformers shall be designed to withstand impulse test voltages and power
frequency test voltage as specification.

13. POTENTIAL TRANSFORMER

The voltage transformer to be supplied under this specification shall be of outdoor, single phase
dead tank double wound, oil immersed type for operation in hot and humid atmospheric conditions
described in this document. To prevent corrosion of the exposed surfaces, the tank should be not
dip galvanized. They shall have separate HV and LV windings and shall be suitable for use as bus
VTs in 33 KV.

13.1 Duty requirement

33KV Voltage transformer for all the indicating instruments, measuring meters and
protection on the 33 KV side.

13.2 Porcelain Insulator

External parts of the voltage transformers which are under continuous electrical stress shall
be of hollow porcelain insulators. The creepage and flashover distance of the insulators

260
 shall be dimensioned and the type and profile designed and shall be suitable for the worst
environmental conditions for heavily polluted atmosphere and shall be not less than 25mm
per KV of highest phase to phase system voltage with protected creepage distance minimum
50 percent of the total. Internal surfaces of hollow insulators shall also be glazed.

The insulators shall be withstand in high mechanical, tensile and breaking strength. All
porcelain used on the voltage transformers shall have the following properties high strength,
homogeneity, uniform glaze, free from cavities and other flaws and a high quality uniform
finish porcelain components shall withstand the maximum expected static and dynamic
loads to which the voltage transformers may be subjected during their service life. The
insulation of the hollow porcelain insulators shall be coordinated with that of the voltage
transformers to ensure that any flash over occurs only externally.

13.3 Core

High grade non-ageing cold rolled grain oriented silicone steel of low hysteresis loss and
permeability shall be used for core so as to ensure accuracy at both normal and or over
Voltage. The flux density shall be limited to 1.6 Tesla at normal voltage and frequency.
There shall be no saturation at any stage during operation.

The instrument security factor of the core shall be low enough so as to cause damage to the
instruments in the event of maximum short circuit current or over voltage.

13.4 Windings

The primary and secondary windings shall be electrolytic copper of high purity and
conductivity and covered with double paper insulation. The conductor shall be of adequate
cross-section so as to limit the temperature rise even during maximum over voltages.

The insulation of windings and connections shall be free from composition liable to soften,
ooze, shrink or collapse during service. The secondary windings of the voltage transformers
shall be suitable for continuous over voltage corresponding to the maximum system voltage
at the primary winding. The winding supports shall be suitable reinforced to withstand
normal handling and the thermal and dynamic stresses during operation without damage.
The voltage transformer secondary circuits will be taken out to form the star point and
earthed at one point outside the voltage transformers.

Both primary and secondary winding terminals shall be clearly and indelible marked to
show polarity. The connections required for different secondary windings in case of multi-
winding voltage transformers shall be clearly indicated in terminal blocks and the wiring
diagrams.

13.5 Secondary Terminal Box

A dust vermin and weather proof terminal box shall be provided at the lower end of each
voltage transformer for terminating the secondary windings. The box shall have a bolted
removable cover plate complete with gaskets. The terminal box shall have cable gland plate
and cable glads with shrouds suitable for entry of 4 core 2.5mm2 PVC insulated
control cables. The terminal box enclosure shall have protection of class IP 55.

261
13.6 Circuit diagram

A durable copy of the circuit wiring diagram shall be affixed to the inner side of the
terminal box cover. Labels shall be provided inside the cover to describe the functions of
various items of equipments.

13.7 Earthing Termination

Two earthing terminals complete with necessary hardware shall be provided on each
voltage transformer for connecting to earth continuity conductors of the Employer. They
shall be of electroplated brass and of adequate size to carry the earth fault current.

The earthing terminals shall be identified by means of appropriate symbol marked in a

legible and indelible manner adjacent to the terminals.

14. DRAWING, MANUALS AND TYPE TEST CERTIFICATES:

The following drawings and manuals shall be furnished for information purpose with each copy of
the bid.

14.1 General Arrangement Drawings indicating all dimensions,

14.2 Technical leaflets/manuals on each piece of Equipment explaining the function of various
parts, principle of operation and special features. Technical leaflets/manuals for offered type
of vacuum bottle etc.

14.3 Type Test Certificates as per IEC carried out on Similar Circuit Breaker from
reputed/recognized laboratory shall be furnished with the bid.

14.4 Supplier also have to provide test reports of relays.

15. CONTRACT DRAWING AND CATALOGUE:

After placement of order, six (6) copies of various drawings data and manuals as mentioned below
shall be submitted to the Project Manager/Employer.

15.1 Dimensional General Arrangement drawing showing all dimensions and disposition of
fittings and space requirement and mounting arrangements.

15.2 Sectional views of contact assembly, operating mechanism and are extinguishing chamber.

15.3 Transport/shipping dimensions with weights.

15.4 Foundation and anchor details including dead-load and impact load with direction and also
point of application.
15.5 Assembly drawing for erection at site with part numbers and schedule of materials.
15.6 Electrical schematic and wiring diagram with explanatory notes, if any.
15.7 Schematic diagram for spring charged operating mechanism schematic layout drawings.

262
15.8 Name plate drawing and any other relevant drawing and data necessary for erection,
operation and maintenance.
15.9 Outline drawings of bushings, terminals and terminal connectors.
15.10 i) After approval, the Contractor shall submit Ten (10) sets of approval drawings and
manuals to the Project Manager/Employer. Instruction manuals and data sheets for each
rating of Equipment shall be submitted. The manuals shall clearly indicate the installation
methods, checkups and tests to be carried out for testing the Equipment and maintenance
procedure.

ii) In all drawings, manuals etc., reference no. of purchase order no. shall be indicated.

iii) Two sets complete in all respects with required bindings should be sent directly to the
Project Manager/ Employer.

16. TEST REPORTS AND INSPECTION:

The test reports are to be submitted along with the bid and Inspections shall be carried out during
Pre Shipment and Post Landing Inspection.
16.1 Type test
The Bidder shall submit along with the bid, detailed as well as complete test reports of all tests
(including Type Test) as stipulated in relevant IEC with Complete identification, date and serial
no., carried out in a Government recognized Test House or Laboratory/ CPRI/ NABL accredited
lab/ on Circuit Breakers of identical design.
For Breaker:
a) Short time withstand and peak withstand current test
b) Lightning impulse voltage withstand test
c) Temperature rise Test
d) Mechanical Endurance Test
e) Measurement of the resistance of the main circuit
f) Short circuit current making and breaking tests g)
Tightness tests.
For CT:
a) Lightning impulse voltage(Chopped impulse and full impulse);
b) Power frequency wet withstand voltage;
c) Temperature rise;
d) Short circuit withstand capability test;
e) Current error and phase displacement
f) Switching impulse.

For PT:
a) Lightning impulse voltage test;
b) High voltage power frequency wet withstand voltage;
c) Temperature rise test;
d) Short circuit withstand capability test;
e) Switching impulse;
f) Determinations of error;

263
16.2 Routine test

For Breaker:
a) Dielectric test on main, auxiliary and control circuit
b) Measurement of the resistance of the main circuit c)
Tightness test
d) Mechanical operation tests
e) Design and visual checks
For CT:
a) Verification of terminal marking and polarity;
b) Power frequency dry withstand test on both windings;
c) Power frequency dry withstand test between sections;
d) Over voltage inter-turn test;
e) Turn ratio;
f) Instrument security factor test;
g) Determinations of error;
h) Secondary winding resistance and Accuracy test ;
i) Current error and phase displacement;
j) Knee point voltage and magnetizing current test ;
k) Insulation Resistance Test;
For PT:
a) Verification of terminal marking and polarity;
b) Power frequency dry withstand tests on both winding;
c) Power frequency withstand tests between sections;
d) Determination of limits of voltage errors and phase displacement;
e) Partial discharge measurement;
f) Insulating Resistance measurement;

16.3 Special tests

For CT:
a) Multiple chopped impulse test on primary winding;
b) Measurement of capacitance and dielectric dissipation test.
c) Mechanical tests.
For PT:
a) Chopped impulse test on primary winding;
b) Measurement of capacitance and dielectric dissipation test.
c) Mechanical tests.
d) Transmitted over-voltage measurement.

17. SPECIFIC LIMIT OF AUXILIARY SUPPLY VOLTAGE:

a) The auxiliary supply voltage shall be 80% to 110% of the rated 110 V in supply for
closing coil and the same shall be 70% to 110% for tripping coil.
b) The operating voltage for motor operated spring charged mechanism shall be 415V
A.C., 3 phase, 50 Hz or 230V. 1-phase, 50 Hz. The motor shall operate at a voltage
variation of 85% to 110% of the supply voltage.

264
18. NAME PLATE:

i. Rated voltage/Maximum voltage

ii. Rated insulation level
iii. Type /Model No./Sl. No./Year of manufacture.
iv. Rated current
v. Rated frequency.
vi. Rated short Circuit Breaking Current.
vii. Rated transient recovery voltage for terminal fault.
viii. Rated short circuit making current.
ix. Rated operating sequence.
x. Rated short time current.
xi. Rated line charging/breaking current
xii. Rated Cable charging current.
xiii. Rated single capacitor bank charging/breaking current.
xiv. Rated small inductive breaking current.
xv. Rated Supply Voltage of auxiliary circuits.
xvi. Applicable standard.

19. RECOMMENDED SPARES:

Instructions to Bidders: The Bidder shall quote item-wise price of recommended spares for 5 (five)
years normal operation. The Employer will decide the actual quality of spare to be procured on the
basis of the List.
20. ACCESSORIES:
Each Breaker shall be furnished complete with fittings and accessories as listed below (The list is
illustrative & not exhaustive).

i. Clamp-type terminal connectors for ACSR Conductor

ii. Base frame and foundation/anchor bolts.
iii. Operating mechanism, trip and close coils.
iv. Set of valves required for gas filling.
v. Auxiliary Contacts and Relays/Contacts.
vi. Local/Remote selector Switch and Close/Trip Control Switch.
vii. Manual close and trip devices.
viii. Mechanical ON/OFF indicators.

ix. Operation counters.

x. Weatherproof Control cubicle and operating mechanism boxes, with locking
arrangement.
xi. Set of Switch-Fuse/MCB/MCCB units for A.C. & D.C. Supply.
xii. Space heaters with thermostat and switch. Two units will be provided with the
option to operate separately.
xiii. Cubicle illumination Lamp with Switch.
xiv. Terminal blocks and internal wiring.

265
 xv. Necessary all Main Control cables & Auxiliary Control cables.
xvi. G.I. conduits and accessories for connection between Central Control Cubicle and
operating mechanism boxes where applicable.
xvii. Other standard accessories which are not specified, but are necessary for efficient
and trouble free operation shall be supplied.

21. TEST AT FACTORY AND TEST CERTIFICATES

21.1 All Acceptance tests shall be carried out at manufacturer’s works in presence of the
Employer’s and Contractor’s representatives. In addition to above, all routine tests are also
to be carried on the breakers as per relevant IEC. The entire cost of acceptance and routine
test that to be carried out as per relevant IEC’ shall be treated as included in the quoted price
of breakers. The Contractor shall give at least 21(twenty one) days advance notice
intimating the actual date of inspection and details of all tests that are to be carried out from
the date when the tests will be carried out.

21.2 Routine tests on all breakers, CTs and PTs shall be carried out as per IEC-62271-100, IEC
60044-1, IEC 60044-2 and test reports shall be submitted along offer.

22. WARRANTY
The Contractor shall warrant that the VCB furnished have conformed to this specification. The
warranty shall state that if, within three (3) years from the date of delivery in case of EXW
contracts & from the date of arrival at the designated port of entry in case of CIP Contracts, a VCB
is found to have defects in workmanship or material (or fails in service due to such defects) the
Contractor shall repair or replace such defective parts (and other parts damaged as a result) within
15 days, free of charge.

266
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 33 KV OUTDOOR TYPE VACUUM CIRCUIT BREAKER (VCB)
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the tender.
Sl. No. Description Unit Tenderers
REB
Guaranteed
Requirements
Values
1 System voltage KV 33
2 Rated voltage KV 36
3 Rated frequency HZ 50
Rated normal current
4
Incoming Feeder A 2000
X-mer Incoming Feeder A 1250
5 Interrupting medium Vacuum
6 Number of phases 3
7 Rated short-circuit breaking KA 31.5
current
8 Rated short-circuit making KA 80
current
9 First pole to clear factor 1.3
10 Rated operating sequence O-0.3s-CO-3min-CO
11 Rated duration of short circuit Sec 3
12 Impulse withstand on 1.2/50 KV 170
s wave
13 Power frequency test voltage KV 70
(dry) at 50Hz,1 min
14 Circuit breaker operating Gang operated spring
mechanism type charged stored energy.
15 Operating particulars
a) Breaking time ms <60ms
b) Closing time ms 70±10ms
16 Is the circuit breaker trip free Yes/No Yes
with anti-pumping feature?
17 Trip coil voltage VDC 110
18 Rated supply voltage of shunt VDC 110
opening release
19 Spring charging motor voltage VAC 415/230
20 Minimum clearance in air
a) Between phases mm 430
b) Phases to earth mm 380
21 Degree of protection IP 55
22 Auxiliary Contact
NO Nos 9
NC Nos 9
23 Is lockout facility fitted Yes
24 Rated breaking current :
Line charging KA 25
Cable charging KA 50
Small inductive KA 02
25 Installation Outdoor

267
Sl. No. Description Unit Tenderers
REB
Guaranteed
Requirements
Values
26 Creep age Distance mm/kv 25
27 Closing Coil Nos. 01

28 Contact Resistance µ ≤ 40
29 Is the lockout facility fitted? Yes
30 Length of stroke mm To be mentioned
31 All current carrying parts of Copper
VCB shall be made of
32 Tripping Coil Nos. 02
33 No of operation
a) At rated short circuit Nos. 100
current Nos. 30000
b) At rated current

34 Standard IEC 62271-100

35 Manufacturer's name &
To be mentioned
Country
36 Manufacturer of vacuum bottle Siemens/ABB
or/ALSTOM

268
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE FOR
33 KV CONTROL AND ENERGY METERING PANEL
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the tender.
Tenderers
REB Guaranteed
SL. No. Description Unit Requirements Values
1 Manufacturer's name & Country To be mentioned
2 Model Number To be mentioned
3 Overall dimensions mm To be mentioned
4 Weight of panel Kg To be mentioned
PROTECTION
A. DIFFERENTIAL RELAY
1 Manufacturer's name & Country Siemens, Germany
/ABB,
Sweden/Schneider
(UK/France)/ GE,
USA
2 Model Number - To be mentioned
3 Type of relay Numerical
-
Programmable
4 Range setting
% of
a) Phase element of current
CT To be mentioned
b) Earth fault element of current
rating
c) Range of time setting
5 Shall have event record option Yes
6 Burden of relay at 10 time CT rating VA To be mentioned
7 Percentage of current setting at
% To be mentioned
which relay will reset
8 Reset time after removal of 10 time
CT rated current for
Sec To be mentioned
a) Phase element (100%)
Sec To be mentioned
b) E/F element (40%)

9 The relays should be 61850 protocol Yes

type.
B. IDMT OVER CURRENT & EARTH FAULT RELAY
1 Manufacturer's name & Country Siemens, Germany
/ABB,
Sweden/Schneider
(UK/France)/ GE,
USA
2 Model Number - To be mentioned
3 Type of relay Numerical
- Programmable
4 Range setting
a) Phase element of current % of CT
b) Earth fault element of current rating 5% to 2500% 1%
c) Range of time setting to 1000% 2.5% to
1000%
5 Ranges of timing at DMT ms 0-100000

269
 Tenderers
REB
SL. No. Description Unit Guaranteed
Requirements
Values
6 Shall have event record option Yes
7 Burden of relay at 10 time CT rating VA To be mentioned
8 Percentage of current setting at
which relay will reset % To be mentioned
9 Reset time after removal of 10 time
CT rated current for Sec To be mentioned
a) Phase element (100%) Sec To be mentioned
b) E/F element (40%)
10 Annunciator for the Transformer
To be provided
Panel
11 The relays should be 61850 protocol Yes
type.
12 Over Current Relay Type Directional

KWh METER Separate Panel for

Energy Metering
1 Manufacturer's name & Country Siemens (Germany/
Switzerland)/Alstom
(UK)/ ABB
(Sweden)/AEG
(Germany)/
Schlumberger
(USA)/ Landys+Gyr
(Switzerland/Greece)
/ CEWE (UK)
2 Model Number - To be mentioned
3 Number of KWh Meters 01
4 Type of the meter Numerical
Programmable,
Multifunction with
accuracy Class 0.2s,
Load profile ,
instrumentation
profile for minimum
6 months with a
interval of 30 min,
software for
protection and
optical probe for
data download as per
IEC with provision
of communication
port automatic meter
reading (AMR)
5 Class of accuracy 0.2 s

270
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR INDICATION METER (VOLT, AMPERE, KW, KVAR, POWER FACTOR,
FREQUENCY)
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the tender.

Tenderers
REB
SL. No. Description Unit Guarantee
Requirement
d Values
1 Manufacturer's name & Country s
Siemens
(Germany/
Switzerland)/
Alstom (UK)/
ABB
(Switzerland/Roma
nia/ Finland)/AEG
(Germany)/
Schlumberger
(USA)
2 Model Number To be mentioned
3 Number of Meters 3 nos Ammeter, 3
nos voltmeter,
1nos KW
meter,1nos KVAR
meter,
1nos Pf meter,1
4 Type of meter nos Digital
frequency
5 Class of accuracy meter.
1

271
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE FOR 33KV
CURRENT TRANSFORMER (CT)
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected)
Failure to provide all of the information requested may lead to the rejection of the tender.

Tenderers
REB
SL. No. Description Unit Guaranteed
Requirements
Values
1 Type Electromagnetic
induction, single
phase, oil
immersed outdoor
2 Rated primary current for Incoming Ams 2000-1000A
Rated primary current for Outgoing Ams 800-400A
3 Rated secondary current Ams 5-5-5A
4.1 Rated secondary accuracy and
burden (33 kV Feeder Breaker)
a) Protection (core 1) 5P20, 30VA
b) Metering (core 2- dedicated 0.2, 30VA
for energy metering)
c) Metering(core 3- for 0.2, 30VA
indicating meters)
4.2 Rated secondary accuracy and
burden (10/14 MVATrans.
Incomer)
a) Metering(core 1- for metering) 0.2, 30VA
b) Protection (core 2) 5P20, 30VA
c) Protection (core 3) 5P20, 30VA
5 Rated frequency Hz 50
6 System voltage KV 33
7 Rated voltage for equipment KV 36
8 Short time current rating for 3 sec. KA 31.5
9 Extended current rating (% of % 120
rated current)
10 Basic insulation level on 1.2 / 50 KV 170
micro-sec wave
11 Power frequency withstand voltage KV 70
(1 min, 50 Hz)
12 Creep age distance mm/K 25
13 Bushing v Porcelain outdoor type
14 System earthing Effectively earthed
15 Insulation class A
16 Standard IEC60044-1
17 Knee point voltage for protection The value should
(at both ratio): be sufficient to
meet 5P20 at
rated burden and
measured
18 Knee point voltage for metering (at The
CT valuesecondary
should
both ratio): be sufficient
resistance. to
meet
19 Security factor, (FS for the FS<5 <5
metering core)

272
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 33 KV VOLTAGE TRANSFORMER (VT FOR BUS & FEEDERS)
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be
rejected) Failure to provide all of the information requested may lead to the rejection
of the tender.

Tenderers
REB
SL. No. Description Unit Guarantee
Requirement
d Values
1 Type s
Electromagneti
c induction,
single phase, outdoor
2 Rated primary voltage KV 33/ √3
3 Rated voltage for secondary windings KV 0.11 / √3 and 0.11 /
4 Rated secondary burden and accuracy √3
Secondary VA 50VA
winding Core 1 Class 0.2
Secondary
(metering) VA 50VA
winding Core 2 Class 3P
5 Frequency Hz 50
6 Impulse withstand voltage KV 170
(1.2/50 micro sec wave)
7 Cree page distance mm/KV 25
8 System earthing Effectively earthed
9 Power frequency withstand KV 70
voltage (1min)
10 Partial discharge PC ≤5
12 Rated voltage factor 1.2 continuous
1.9 at 30
13 Standard IECsecond
60044-2
14 Short time current rating for 3 sec. KA 31.5

273
 PUBLICATION NO: 1002-1999
BANGLADESH RURAL ELECTRIFICATION BOARD (BREB)
TECHNICAL SPECIFICATION FOR 11 KV INDOOR TYPE
VACUUM CIRCUIT BREAKER/SWITCHGEAR
1. 11 KV Indoor Switchgear

1.1 General

The 11 kV switchgear shall consist of a single bus-bar, metal clad, indoor type, floor
mounted, single tier integrated unit, incorporating enclosures for the circuit breaker units,
bus-bars, current transformers and auxiliary wiring.

Each 11 kV CB shall be provided with a combined relay & control panel forming an
integral part of the circuit breaker equipment. All in door 11 kV feeders/ bus CTs and bus
PTs shall be dry/ cast resin type.

The panels shall be equipped with the necessary protection control devices, indicating
instruments and alarming devices, MCBs, etc. All the relays should be 61850 protocol type
for automation network of the 33/11.55 kV Sub-station.

The switchgear shall be of robust construction designed for maximum reliability of service
in the tropical climate specified.

Cable boxes shall be supplied complete with glands and terminal lugs.

1.2 Clearances

Maximum insulator lengths and clearances in air shall be not less than those specified for 11
kV switchgear having 75 KVp Basic Impulse Level.

1.3 Current Ratings

All parts of the switchgear, including current transformers, shall be capable of withstanding,
without thermal of mechanical damage, the instantaneous peak and the three second short
time current corresponding to the rated making and breaking capacity of the circuit
breakers.

All normal current specified are the minimum continuous values required under the service
conditions appertaining to Bangladesh.

1.4 Circuit Breaker making and Breaking capacities

Each circuit breaker shall be capable of making and breaking short circuit faults in
accordance with the requirements of IEC 56 - Circuit Breaker, at 3 phase symmetrical
circuit ratings at 11 kV service voltages as stated in the schedules.

274
1.5 Circuit Breakers

1.5.1 Type

The 11 kV circuit breakers shall be vacuum type in accordance with IEC 56 as appropriate.

All types shall incorporate horizontal isolation facilities and be mounted on horizontal
draw-out type.

1.5.2 Interchangeability of Circuit Breakers

Circuit breaker of the same type and current rating shall be interchangeable, both
electrically and mechanically, but it must be impossible to interchange equipment of
different current ratings.

1.5.3 Circuit Breaker Operation Mechanism

Circuit breaker closing mechanisms shall be 230-volt a.c motor wound preferably spring
operated type such that the closing speed is independent of the operator.

11kV switchgear tripping shall be effected by means of 02 nos. of 110 volt dc shunt trip
coil.

Each equipment shall be provided with a visual, mechanized, indicating device, which shall
be positively driven in both directions to show whether the circuit breaker is “Open” or
“Closed”. It shall be operative when the circuit breaker is in the “Service” and “Test”
locations. Lamp indication in place of a mechanical indicator will not be accepted.
Operation counters shall be provided on each mechanism.

Means shall be provided for coupling the secondary circuits on the fixed portion to those on
the movable portion when the circuit breaker is isolated in order to permit closing, tripping
and interlock circuits to be checked for operation test purposes.

Means shall be provided for local manual mechanical tripping of circuit breakers, preferably
by push buttons, shrouded to prevent inadvertent operation.
Locking facilities shall be provided so that with the circuit breaker in any location it can be
prevented from being closed when it is open and from being mechanical tripped when it is
closed. This requirement shall be met by the fitting of a single padlock and shall not entail
the fitting of any loose components prior to the insertion of the padlock.
It shall not be possible, without the use of tools, to gain access to the tripping toggle or any
part of the mechanism which would permit defeat of the locking of the mechanical tripping
feature.
It shall not be possible to render the electrical tripping feature inoperative by any
mechanical locking device.
1.5.4 Circuit Breaker Isolating Features
Irrespective of the operating type of unit the following shall apply.
Each circuit breaker shall be connected to the bus bars and feeder circuit through plug and
socket type isolating devices. The devices shall be of the “Off Load Type” but shall be
suitable for operation whilst the bus bars and/or feeder circuits are alive.

275
Isolating devices shall be interlocked with their respective circuit breakers to prevent their
making or breaking load, but arrangements whereby attempted isolation of a closed circuit
breaker trips the circuit breaker are not permitted.

The main circuit isolating devices and also all secondary circuit isolating contacts shall be
of the self-aligning type, mounted in accessible positions to permit maintenance.

The number of auxiliary circuit isolating switches shall be sufficient to meet the facilities.

1.5.5 Interlocks

All mechanical interlocks shall be of the preventive type and shall be arranged to prevent
mal operation as close as possible to the point at which mechanical force is applied, in order
to prevent defeat of the interlocks by distortion of linkages Electrical interlocks shall also
function so as to prevent the closing of the circuit breaker.

Clearly labeled mechanical interlocks shall be provided which are designed to prevent:

a) A closed circuit breaker from being withdrawn or inserted into the isolating contacts.
b) Tripping by attempted isolation.
c) The closing of a circuit breaker except when correctly located in Service or Test
positions.
d) A circuit breaker from being plugged into the isolation contacts if the tank is not in
position
e) A circuit breaker being closed in the service position when the secondary circuits
between the fixed and moving portions are not completed.

In addition electrical interlocks may be utilized to ensure safe operation of the plant; i.e. on
11 kV transformer incoming circuits the circuit earth position shall not be operative unless
the 33 kV circuit is de-energized and isolated etc.

1.5.6 Safety Shutter Devices

A set metal shutters shall be provided to cover each 3 phase group of stationary isolating
contacts.

The shutters shall open automatically by a positive drive initiated by the movement of the
circuit breaker. The closing operation shall also be automatic by positive drive
When padlocked closed, the shutters shall completely shroud the stationary contacts and it
shall not be possible to force the shutters or part of the shutters to gain access to the
stationary contacts.
To facilitate testing, means other than locking shall be provided for securing the shutters in
the open position. However, such means shall be automatically cancelled when the
automatic operation of the shutters restored upon reconnection of the circuit breaker.
Bus-bar shutters shall be painted signal red, colour 537 in BS 381 C, and shall be clearly
and indelibly labeled “BUSBARS” in large white letter in English. The Contractor may
offer works which comply with different standards or codes only if, and when requested by
the Project Manager Circuit shutters shall be painted yellow, colour 355 in BS 381 C, but
shall not be lettered, except that on incoming feeders the circuit shutters shall be clearly and
indelibly labeled “DANGER LIVE CABLES” in large red letters.

276
Voltage transformer spout shutters shall be painted yellow, colour 355 in BS 381 C.
Durable phase colour identification shall be provided in a prominent position. Provision or
access shall be made for lubricating the mechanical linkages.

All shutters shall be effectively earthed

Shutters shall not operate towards the fixed isolating contacts.

1.5.7 Bus-bars and Connections

The equipment shall be of single bus-bar type. Bus-bars and connection shall comply with
applicable clauses of IEC 298 and shall be fully insulated.

The equipment shall be of single bus-bar type. The bus-bar assemblies shall be of a type
which shall not rely only on air for insulation purpose.

Any earthed screen applied to the exterior of the insulation shall be securely earthed in each
bus-bar compartments.

The insulation of the bus-bars and their connections shall be capable of withstanding,
without damage, the thermal and mechanical effect of a through fault current equivalent to
the short-time rating of the switchgear.

Access to bus-bars and the connections directly thereto shall be gained only by the removal
of covers secured by bolts or screws. Such covers shall be marked clearly and indelibly
“BUSBARS”

Bus-bars shall extensible at both ends; such extension shall entail the minimum possible
disturbance to the bus-bar chambers. Compound filled bus-bar chambers are not acceptable.

1.5.8 Earthing of Metal Parts of Switchgear

All metal parts, other than those forming part of an electrical circuit, shall be connected to a
hard-drawn, high conductivity, copper earth conductor on each unit, of adequate sectional
area.

The frame of draw-out circuit breakers shall be connected to the earth bar through a
substantial plug type contact and the plug shall be long enough to allow the bus-bar and
feeder shutters to close before breaking contact.

Interlocking (both mechanical & electrical) must be provided to avoid accidental earthing
circuit breaker in “service position”.
1.5.9 Earthing of Insulations
Earthing of the switchgear and ancillary panels and auxiliary equipment shall be carried out
in accordance with IEEE Standard 80 & 142 where applicable.

1.5.10 Insulators
Porcelain insulators shall be best quality electrical porcelain. The clamping surfaces of all
porcelain insulators shall be accurately ground and shall be free of glaze.
Insulators of moulded or resin bonded material shall have a durable, non-hygroscopic
surface finish having a high anti-tracking index.

277
1.5.11 Auxiliary switch

Each circuit breaker shall be provided with adequate no. auxiliary switches to interrupt the
supply to the closing mechanism and to complete the trip circuit, when the circuit breaker is
in the “Closed” position and to cover all the necessary indication, interlocking and control
facilities with spare contacts.

Each circuit breaker shall be provided with clean auxiliary contacts for the purpose of
providing remote switch and alarm indication at the remote grid supervisory centre. In
addition each circuit breaker shall be provided with the necessary 50 volt dc interposing
relays required to achieve remote control of the circuit breaker via a future remote grid
supervisory system. All auxiliary switches shall be wired down whether in use or not to the
appropriate marshaling kiosk.

1.5.12 Special Tools

One complete set, of all special tools that are necessary for the overhauling maintenance
and adjustment of the whole equipment shall be provided with each switchboard. The tools
provided shall be in a new condition and shall not be used for the erection of the equipment
on Site.

1.5.13 Indoor Breaker Specification

The 11 kV switchgear unit indoor vacuum CB will be draw out type along with CT,11 kV
bus, 11 kV PT (3 × single phase unit – draw out type). The C.B shall have spring operating
mechanism suitable for charging by motor (A.C 230 V, 1 phase) with provision of hand
charging. Sufficient auxiliary contacts shall be provided for position indication, interlocks
and other purposes. Two sets of independently operative trip coils shall be there. Provision
for signaling of low gas pressure and ultimate lock out for very low pressure shall be
provided. Anti pumping features should be introduced with the Breaker. All the current
carrying parts should be copper.

Technical Particulars of 11 kV Circuit Breakers:

Phase 3-phase
Service (Rated) Voltage 11.55 KV
Maximum system Voltage 12.62 KV
2000 Amps.
Continuous rating current of Bus-bar
2000 A (Incomer for 20/28 MVA),
Continuous rating current
2000 A (Incomer for 10/14 MVA),
2000 A (Bus Section),
630A (Feeder).

Basic Impulse Level (BIL) 75 kV,

Power frequency withstand voltage 28 kV.

Bus Shall be 3 phase, 50Hz ,2000A, air insulated capable of withstanding 31.5 KA for 3 sec.

278
Vacuum Interrupter

The vacuum interrupter, consisting of fixed contact and moving contact, shall be
interchangeable among the same type interrupter. Short circuit capacity of vacuum bottle
should be 31.5 KA and design life should be 100 nos. Operation at rated short circuit level.
The operation of the interrupter will be 30000 nos. at rated current.

Vacuum Bottle shall be from Siemens/ABB or/ALSTOM and of reputed indigenous make.
Offered bottle shall be identical with Type tested one. Brochures/leaflet on technical data
sheet for vacuum bottle shall be enclosed with technical bid.

1.5.14 Current Transformers (CTs).

The current transformer rated current ratio shall match the connected load circuit and
secondary circuit requirements.

Current transformers shall be capable of withstanding without damage the full load, peak
and rated short time currents of their associated equipment.

Where space within a current transformer chamber permits dedicated current transformers
shall be used for protection, instrumentation and metering. All the indoor 11 kV CTs shall
be dry/ cast resin type.

Current transformers used for energizing indicating instruments and metering shall be of
Class 0.2 accuracy in accordance with IEC 185Current transformers for protective and
protective/indication purposes shall be designed to suit the particular requirements of the
associated protection, which in general shall be in accordance with the recommendations
given in BS 3938 or approved equivalent.

Class 5p current transformers shall be used for inverse time over-current and/or earth fault
protection. The rated accuracy limit current shall be equivalent to the maximum
symmetrical three phase fault current or earth fault current of the protected circuit or
equivalent to the switchgear breaking capacity unless otherwise approved by the Project
Manager.

The current transformers shall be capable of meeting the 5p error classification at rated
accuracy limit current over the full range of relay settings, unless otherwise approved by the
Project Manager.

Current transformers used for indication/metering purposes shall be designed to saturate at a

value of primary current sufficiently low to protect the secondary circuit from damage at all
possible values of primary fault current up to the associated primary short time thermal
rating.
Current transformers for combined purposes (e.g. protection relays and indicating meters)
shall have a dual Class 5p/Class 0.2 performance, and the secondary circuit shall have an
approved means (saturating reactor or saturating interposing C.T.) of protecting the meters
and reducing their burden under system fault conditions.
The rated volt-amp output of each current transformer shall not be less than 110% of the
connected burden as installed in service, the burden of cable connections being taken into
account.

279
The secondary windings of each set of current transformers shall be earthed at one point
only via an accessible bolted disconnecting link, preferably located within the relay cubicle.

Where double-ratio secondary windings are specified provided a label shall be provided at
the secondary terminals of the current transformer indicating clearly the connections
required for either tap. The connections and the ratio in use shall be indicated on all
connection diagrams.

Design magnetization curves and dc resistance values shall be submitted before

manufacture for each current transformer used for protective purposes and shall be
subsequently verified by works routine tests and also by site commissioning tests.

Where current transformers have to operate or be mounted on apparatus provided under

other contracts, the Contractor shall be responsible for ensuring design and installation
compatibility with other Contractors and for keeping the Project Manager informed.

Metal clad switchgear current transformers shall be located on the non-bus-bar side of the
circuit breaker except where current transformers are provided on both sides of the circuit
breaker for protection zone overlap. The primary conductors shall be accessible for primary
current injection treating on site.

1.5.15 Voltage Transformers (VTs)

Voltage transformers shall comply with the requirements of IEC 186 with amendments and
supplements and shall be of:-

Class 3P accuracy for protection/indicating instruments

Class 0.2 accuracy for tariff metering or acceptance efficiency testing.

The VA output shall be 50% in excess of the design requirements except for tariff metering
voltage transformers which shall be at least 10% in excess of the design requirements.

For tariff metering voltage transformers the Contractor shall check the total installed
secondary burden and if necessary shall install dummy burdens to achieve the calibrated
accuracy.

Voltage transformer secondary circuit shall be earthed at one point only and metal cases
shall be separately earthed. The transformers core, where accessible, shall also be separately
earthed. All the indoor 11 kV VTs shall be dry/ cast resin type.

All voltage transformers in the system at a given voltage level shall be earthed in the same
manner.

Where it is required to earth the primary neutral of a metal clad three- phase voltage
transformer, the neutral earthing connection shall be insulated and brought out separately
from the tan earthing connection. Means shall be provided to maintain the tank earthing
connection while the voltage transformer is being withdrawn.

280
 Where three single-phase voltage transformers are supplied for protection purposes, star
connected secondary windings shall have the star point formed by insulated connections and
shall be earthed at a common point.

Where necessary for earth fault protection, voltage transformers shall be of five- limbed
core construction.

Where possible primary windings shall be connected through fuses with current limiting
features.

Secondary MCB’s shall be provided as close as possible to each voltage transformer and
labeled to show their function and phase colour. The secondary circuits shall be monitored
individually to detect and alarm individual fuse failure or MCB trip and to block protection
operation if required.

Voltage transformers shall be designed that saturation of their cores does not occur when
1.732 times normal voltage is applied to each winding.

Magnetization curves shall be submitted for approval for each type of voltage transformer.

The standard secondary voltage between phases shall be 110 volts unless special
circumstances dictate otherwise, and are approved by the Project Manager.

Secondary circuits from different voltage transformers, or separate windings of the same
transformer, shall not be connected in parallel.

Voltage transformers shall be connected on the non-bus-bar side of circuit breakers unless
otherwise approved by the Project Manager.

1.6 TEST CERTIFICATE OF 11 KV INDOOR TYPE CIRCUIT BREAKER.

Instructions to Bidders: Bidders shall submit with their offer the test certificates along with
the test results of 11 KV Panel board including Circuit Breaker for the following tests
carried out in accordance with IEC-56 and other international standard or latest revision
thereof from an internationally recognized independent and reputable testing authority like
KEMA- Holland/CESI Italy/UL-USA etc.
A. Type Tests:
For Breaker:
a) Short time withstand and peak withstand current test
b) Lightning impulse voltage withstand test
c) Temperature rise Test
d) Mechanical Endurance Test
e) Measurement of the resistance of the main circuit
f) Short circuit current making and breaking tests

281
For CT

a) Lightning impulse voltage(Chopped impulse and full impulse);

b) Power frequency wet withstand voltage;
c) Temperature rise;
d) Short circuit withstand capability test;
e) Current error and phase displacement
f) Switching impulse.
For PT:
a) Lightning impulse voltage test;
b) High voltage power frequency wet withstand voltage;
c) Temperature rise test;
d) Short circuit withstand capability test;
e) Switching impulse;
f) Determinations of error;
For Control Panel & Relays:
Required tests as per relevant IEC 62271-111 Standard.
B. Routine test
For Breaker:
a) Dielectric test on main, auxiliary and control circuit
b) Measurement of the resistance of the main circuit c)
Tightness test
d) Mechanical operation tests
e) Design and visual checks
For CT:
a) Verification of terminal marking and polarity;
b) Power frequency dry withstand test on both windings;
c) Power frequency dry withstand test between sections;
d) Over voltage inter-turn test;
e) Turn ratio;
f) Instrument security factor test;
g) Determinations of error;
h) Secondary winding resistance and Accuracy test ;
i) Current error and phase displacement;
j) Knee point voltage and magnetizing current test ;
k) Insulation Resistance Test;
For PT:
a) Verification of terminal marking and polarity;
b) Power frequency dry withstand tests on both winding;
c) Power frequency withstand tests between sections;
d) Determination of limits of voltage errors and phase displacement;
e) Partial discharge measurement;
f) Insulating Resistance measurement;
Note: The test certificate for 3 phases, 50 Hz, 11 KV circuit breaker of rated current offered
for the type (Manufacturer’s designed type) shall be submitted. However, the test
certificates for circuit breakers of the offered manufacturer’s designated type and voltage
class as per requirement of the bidding document but having higher rated current shall also
be accepted. All the aforesaid tests shall be carried out in one random selected circuit
breaker. Parts of the tests carried out on different circuit breakers shall not be accepted. The
bid will be considered non responsive in absence of test certificates and the supply records.

282
INCOMING SWITCHGEAR UNIT:

Description Unit BREB/PBS Requirement Tenderer’s Guaranteed Values

Manufacturer's
Siemens /ABB or / ALSTOM
Name & Address

Manufacturer's
Name & Address
Siemens /ABB or / ALSTOM
Vacuum bottle
manufacturer
Applied standard
Rated nominal
kV 11
voltage
Rated voltage kV 12
Rated current for
A 2000
bus
Rated short time
kA 31.5
current
Short time
current rated Sec. 3
duration
Circuit Breaker:
Type VCB
Rated Voltage kV 12

2000A for 10/14MVA

Rated current A
substations

Rated short Ckt.

Breaking current, kA 31.5
3 sec
Rated short Ckt.
kA 80
Making current
Rated breaking
Cycle 3
time
Opening time Sec.
Closing time Sec.
Rated operating
0-0.3 sec-co 3 min-co
sequence
Control Voltage V DC 110
Motor voltage for
V AC 180~240
spring charge
No. of Trip coil No. 02
Current Transformer:
Rated Voltage kV 12
Accuracy class,
0.2
Metering
Accuracy class,
5P20
Protection

283
Rated Current
A 1600-800:5-5-5
ratio

Burden VA 20
Rated frequency Hz 50
Insulation level:

AC withstand
voltage 1 min. kV 28
dry
Impulse
withstand, full kV 75
wave
Degree of Protection:
Enclosure IP3X
HV Compartment IP65
LV Compartment IP40
Earthing Switch:

Type
Short time
kA
current, 3 Secs.
Bus bar:
Material Copper
Cross Section mm2
Dimension and Weight
Height mm
Width mm
Depth mm

Weight including
Kg.
Circuit Breaker
BUS SECTIONALIZER SWITCHGEAR UNIT:

Manufacturer's
Name & Address

Applied standard
Rated nominal
kV 11
voltage
Rated voltage kV 12

Rated current for

A 2000
bus

Rated short time

kA 31.5
current
Short time
current rated Sec. 3
duration
Circuit Breaker:
Type VCB
Rated Voltage kV 12

284
Rated current A 2000

Rated short Ckt.

Breaking current, kA 31.5
3sec
Rated short Ckt.
kA 80
Making current
Rated breaking
Cycle 3
time
Opening time Sec.
Closing time Sec.
Rated operating
0-0.3 sec-CO-3 min-CO
sequence
Control Voltage V DC 110
Motor voltage for
V AC 180~240
spring charge
No. of Trip coil No. 02
Current Transformer:

Rated Voltage kV 11
Accuracy class,
5P20
Protection
Accuracy class,
0.2
Metering
Rated Current
A 2000-1000:5-5
ratio

Burden VA 20
Rated
Hz 50
frequency
Insulation level:

AC withstand
voltage 1 min. kV 28
dry
Impulse
withstand, full kV 75
wave
Degree of Protection:
Enclosure IP3X
HV Compartment IP65
LV Compartment IP40
Earthing Switch:

Type

Short time
kA
current, 3 Sec.
Bus bar:
Material Copper
Cross Section mm2
Short time
KA
current, 3 Sec.

285
Dimension and Weight

Height mm
Width mm

Depth mm
Weight including
Kg.
Circuit Breaker
LINE FEEDER SWITCHGEAR UNITS:

Manufacturer's
Name & Address

Applied standard
Rated nominal
kV 11
voltage
rated voltage kV 12

Rated current A 2000

Rated short time

kA 31.5
current
Short time
current rated Sec. 3
duration
Circuit Breaker:

Type VCB
Rated Voltage kV 12

Rated current A 630

Rated short Ckt.

Breaking current, kA 31.5
3sec
Rated short Ckt.
kA 80
Making current
Rated breaking
Cycle 3
time
Opening time Sec.
Closing time Sec.
Rated operating
0-0.3 sec-CO- 3 min-CO
sequence
Control Voltage V DC 110
Motor voltage for
V AC 180~240
spring charge
No. of Trip coil No. 02
Current Transformer:
Rated Voltage kV 12
Accuracy class,
0.2
Metering
Accuracy class,
5P20
Protection
286
Rated Current
A 600-300: 5-5
ratio

Rated short time

kA 31.5
current, 3 Sec

Burden VA 20
Knee point
Sufficient to meet 5P20 at
voltage for
rated burden and measured
protection (at
CT secondary resistance
both ratio)
Rated
Hz 50
frequency
Insulation level:

AC withstand
voltage 1 min. kV 28
dry
Impulse
withstand, full kV 75
wave
Degree of Protection:

Enclosure IP3X
HV Compartment IP65
LV Compartment IP40
Earthing Switch:

Type Earthing Truck

Short time
kA
current, 3 Secs.
Bus bar:
Material
Cross Section mm2
Dimension and
Weight
Height mm
Width mm
Depth mm

Weight including
Circuit Breaker
Kg.

VOLTAGE TRANSFORMER SWITCHGEAR UNITS

Type

Bus bar

287
Material Copper

Cross Section mm2

Rated nominal
kV 11
voltage
rated voltage kV 12
Rated current for
A 2000
bus
Rated short time
kA 31.5
current
Short time
current rated Sec. 3
duration

Number of phase
Rated primary
kV 11/√3
voltage
Rated secondary
V 110/√3
voltage
Rated tertiary
V 110/√3
voltage
Rated burden,
VA 50
Secondary
Rated burden,
VA 30
Tertiary
Accuracy class
0.2
for Metering
Accuracy class
3P
for Protection
Power Fuse:
Rated voltage kV 12
Rated current A 10
Rated short Ckt.
kA 31.5
Breaking current
Dimension and
Weight
Height mm
Width mm
Depth mm
Wt. including
voltage Kg.
transformer
Degree of
Protection:
Enclosure IP3X
HV Compartment IP65
LV Compartment IP40
Insulation
kV
level:
All Current
carrying path
of the breaker
should be
copper

288
11KV CONTROL AND ENERGY METERING PANEL

PROTECTION

Schneider, UK or France /
Manufacturer's
Siemens, Germany / ABB,
name & Country
Sweden / GE, USA

Model Number To be mentioned

Type of relay Numerical Programmable

Range setting
a) Phase element
5% to 2500%
of current
b) Earth fault % of
element of CT 1% to 1000%
current rating
c) Range of time
2.5% to 1000%
setting (IDMT)
Ranges of timing
Sec. 0-100 (with 1ms interval)
at DMT
Shall have event
Yes
record option
Burden of relay
at 10 time CT VA To be mentioned
rating
Precentage of
current setting at
% To be mentioned
which relay will
reset
Reset time after removel of 10 time CT rated current for

a) Phase element
Sec. To be mentioned
(100%)
b) E/F element
Sec. To be mentioned
(40%)
The relays should
be 61850
protocol type
KWh Meter
Siemens
(Germany/Switzerland)/Alstom
Manufacturer's
(UK)/ABB (Sweden)/
name & Country
AEG(Germany)/Schlumberger(
USA)/Landis Gyr (Switzerland)
Model Number To be mentioned
Number of KWh
1
Meters

289
 Numerical Programmable,
Multifinction with accuracy
Class 0.2s, Load profile,
instrumentation profile for
minimum 6 months with a
Type of the
interval of 30 min, software for
meter
protection and optical probe
for data download as per IEC
with provision of
communication port automatic
meter reading (AMR)
Class of accuracy 0.2s
Indication meter (Volt, Ampere, kW, KVAR, Power Factor, Frequency)

Siemens
Manufacturer's (Germany/Switzerland)/Alstom
name & Country (UK)/ABB(Sweden)/AEG(Germ
any)/Schlumberger(USA)

Model Number To be mentioned

3 nos Ammeter, 3 Nos

Number of Voltmeter, 1 Nos KW Meter,
Meters 1 Nos KVAR meter, 1 Nos Pf
meter, 1 Nos frequence meter

01Nos. multifunction meter

Multifunction containing ( 1 Nos KW Meter,
Meter 1 Nos KVAR meter, 1 Nos Pf
meter, 1 Nos frequence meter)

Type of the
Digital
meter
Class of accuracy 1

290
 PUBLICATION 266-1999
BANGLADESH RURAL ELECTRIFICATION BOARD (BREB)
PEOPLES REPUBLIC OF BANGLADESH
STANDARD FOR
36 KV UNDERGROUND POWER CABLE
1. GENERAL

This standard establishes the physical and electrical requirements for 36 KV, 1-Core, copper
conductor, cross-linked polyethylene (XLPE) insulated power cable shall comply with IEC-60502.
The cable shall be suitable in all respect for use in 33 KV system, 50 hertz, underground
distribution system.

2. REFERENCE DATA:

REB 36 KV, 1- core underground cable shall be comprised of the following:

2.1 CONDUCTOR

The conductor shall be stranded, circular and compacted copper wire in accordance with
IEC-228 or ASTM B3.

2.2 CONDUCTOR SCREEN

The conductor screen shall comprise of a layer of extruded semi-conducting compound,

compatible in all respects with the conductor and insulation material. Conductor screen
shall be bonded to the insulation such a way that no voids or discontinuities are present. The
bond shall be adequate to withstand normal electrical and mechanical stresses in service
without degradation or separation.
Lapped semi-conducting tape shall not be used for conductor screens.

2.3 INSULATION
The insulation shall be cross-linked polyethylene (XLPE). The cable insulation shall be
extruded in one operation with conductor & insulation screens. The highest possible purity
of insulation material is required. The Bidder shall demonstrate that adequate precautions
are taken to remove contaminants and to eliminate the introduction of particles of
contaminate during material handling or the extrusion process.

The insulation material shall consist of cross-linked polyethylene tightly extruded over the
conductor screen. A cross-linking process using steam curing will not be permitted. Dry
process insulation shall be offered, without which the bid will not be considered.

2.4 INSULATION THICKNESS

The insulation thickness of the cables shall not be less than the values tabulated in IEC
publication 60502. Insulation thickness shall not depart from the specified nominal value by
an amount exceeding the tolerance specified in IEC publication-60502. The thickness of the
semi conducting screens on the conductors and over the insulation shall not be included in
the measurement of insulation thickness.

2.5 INSULATION SCREEN

291
 The insulation screen shall comprise of a non-metallic semi-conducting polyethylene part in
combination with a metallic part.

The non-metallic semi-conducting part shall be applied directly upon the insulation of each
core and shall comprise of a layer of extruded semi-conducting polyethylene compound.

The conductor screen, Insulation and semi-conducting part of Insulation screen layer shall
be applied to the conductor in common extrusion process with dry curing system.

The metallic part shall be stranded copper applied directly over the semi-conducting part.It
shall comprise of a single layer of copper wires equally spaced apart.

2.6 ARMOUR

The armour shall consist of a single layer of non-magnetic wires in accordance with IEC-
60502.

The non-magnetic wire joints are brazed or welded and any wire shall be not less than 1 mm
from nearest joints in any other armour wire in the complete cable.

2.7 OVER SHEATH

The cable shall be sheathed overall with a PVC (polyvinyl chloride) outer sheath. The outer
sheath shall be of smooth and uniform composition and free of holes. Cracks blisters and
imperfection.
As a protection against termite attack, the outer covering shall contain termite repellent
substance of Pb nephtanate.
The outer sheath shall be of adequate strength and thickness to withstand the test voltages
and mechanical tests and shall be suitable for the ambient conditions at site.

The outer sheath material shall be capable of withstanding without damage or deformation
the highest temperature achieved with the cable at its rated current and at the site ambient
conditions.

2.8 MANUFACTURER’S IDENTIFICATION

The manufacturer’s identification shall be printed with black colour on the identifying tape.
It shall show the rated voltage, conductor size, year of manufacturing and name of the
manufacturer at an interval of not more than 1000 mm throughout the length of the cable.
The designation of voltage and cable marking shall also be embossed on the outer PVC
covering. The gap between the end of one set of embossed characters and the beginning of
the next shall be not greater than 150 mm throughout the length of cable with character
approximately 10 mm high. Name of the Employer shall be embossed in the title-
“BANGLADESH RURAL ELECTRIFICATION BOARD (BREB)” at every 1000 mm
gap.

2.9 CONTINUOUS CURRENT RATING:

The continuous rating of the cables that the bidder proposes to supply shall be calculated by
means of the procedure described in IEC publication 60287based on the site ambient
conditions including solar radiation, with the installation parameters as specified.

The maximum conductor temperature shall not exceed 900 C when carrying the rated
292
 current under the most onerous site conditions.

The Contractor shall base his ratings on the site ambient conditions, with the methods of
installation and bonding as specified. Due account shall be taken of the heating due to other
cables or other sources of heat where these can be identified. The Contractor shall state all
the parameters including any assumptions that he has made in the calculation of continuous
current ratings.

2.10 SHORT CIRCUIT RATING:

All cables shall be capable of withstanding without damage or permanent distortion the
specified maximum short circuit currents for the specified times as under: -

The temperature of the conductors during the passage of the specified maximum fault
current for the specified time of one second shall not exceed 250 C for XLPE cables.

The cable design including the design of external Clamps or other restraining devices shall
be adequate to contain the mechanical forces arising from two or three phase short circuit
currents and longitudinal forces whether arising from magnetic effects or from thermal
expansion of conductors.

The cable metallic screen sheath and armor shall be capable of passing the specified
maximum earth fault current for the specified time of one second without damage,
permanent distortion or deterioration in the cable. The insulation screen shall be capable of
carrying an earth fault current of 31.5 KA for 3 second without damage.

If in order to comply with the requirement for carrying prospective earth fault current it is
necessary to rely on the armor and/ or sheath conductivity in addition to metallic core
screen tapes, the bedding material or materials shall be of the semi-conducting type.

3. TESTS:

3.1 GENERAL

The following tests shall be carried out to demonstrate the integrity of the cable.
The frequency of the alternating current supply is between 48 Hz and 62 Hz.

3.2 TESTS AT MANUFACTURER’S WORKS

Tests shall be carried out in accordance with the relevant British standards IEC publication
and the following type tests and routine tests shall be carried out at the Manufacturer’s
works.

293
 a) TYPE TESTS

Type test for 36 KV cables shall be carried out in accordance with the IEC publication 540
and 60502 for suitable length of cable.

I) ELECTRICAL TESTS

1. Partial Discharge test (s).

2. Bending test.
3. Heat cycle test.
4. Impulse Voltage withstand test
5. High voltage Alternating current test

II) NON-ELECTRICAL TEST

1. Measurement of Insulation thickness

2. Measurement of thickness of non-metalic sheath.
3. Determination of mechanical properties of insulation and sheaths before
and after aging.
4. Ageing test on pieces of complete cables.
5. Pressure test at high temperature on insulation &sheaths.
6. Hot set test.
7. Water absorption test on insulations.
8. Shrinkage test on XLPE insulation.
9. Electrical test after installation.
10. Water penetration test.

b) ROUTINE TESTS:

The manufacturer shall carry out routine tests on all finished cables to demonstrate their
individual integrity as per IEC pub. 60502

1. Measurement of Electrical Resistance of conductors.

2. High voltage test
3. Partial discharge test

3.3 SPECIAL TEST

Additional samples of cable shall be selected for special tests. The number and frequency of
special tests shall be in accordance with the procedures specified in IEC publication 60502.
The cable shall be subjected to the following special tests.
1. Conductor examination
2. Check of dimensions
3. Electrical test for cables
4. Hot set test

294
4. PACKING

Cable shall be shipped on standard non-returnable steel drum, each drum having stenciled on its
side ; Size, Type, and length of cable, gross & net weight and contract number. The complete cable
drum shall be covered by steel sheet to protect from external thrust and the kits are to be export-
packed and properly protected for shipment, rough transportation and storage.

The maximum length of cable on a drum shall be 500 meters with a variation of + / - 10 %(ten
percent) and it shall be only one length of conductor on a reel.

Each kits cartoon shall be sealed in water proof polyethylene bag having a silicagel packet placed
inside the unit and then packed in polystyrene foam gasket closed by self adhesive tape. Size of the
items shall be marked by label on the foam for easy identification. Maximum 10 (ten) sets kits are
allowed to pack into separate wooden packing box lined with heavy gauge polyethylene.

5. DOCUMENTATION

The following test reports and the attached data schedule filled in completely shall be included with
offer, without which the offer shall not be considered for evaluation.

a) All Routine Test, Type Test and Special Test reports as per clause 3.2a, 3.2b & 3.3 of the
specification and ISO-9001 Certificate of the identical 36KV cables from an internationally
recognized independent laboratory.

b) Supply record with documentary evidence of the identical 33KV cables for last 5 (five)
years mentioning the employer’s name, quantity, and year of supply.

c) Printed catalogue/Leaflet for the offered type of cables.

6. GENERAL REQUIREMENT OF 33 KV XLPE UNDERGROUND CABLE

Table-1

SL. No. Particulars Specified

1. Installation Direct burial
2. Type XLPE insulated, 1-core, armoured,
underground cable.
3. Voltage:
a. Voltage between phases 33 KV
b. Maximum system voltage 36 KV
4. CORES:
Number of cores Single core, stranded copper, round
concentric.
5. CONDUCTOR:
a. Material copper
b. Design (stranded sectional etc.) round, compacted
c. Strand As per table-2
d. Cross sectional area of As per table-2 or specified as per
conductor core material & price schedule
e. Maximum DC resistance of As per table-2
conductor at 200 C

295
 6. CONDUCTOR SCREEN:
a. Material Extruded Semi-conducting PE
7. INSULATION:
a. Thickness (Nom) 8.00 mm
b. Type of curing Dry curing
8. INSULATION SHIELD Extruded Semi-conducting PE
9. ARMOUR: A single layer of non-magnetic wires in
accordance with IEC 60502.
10. OVER SHEATH PVC
11. STANDARDS Design, Manufacture, Testing &
Performance shall be in accordance to
latest revision of IEC-60502,540 or
Equivalent International Standard.
Table-2

Conductor XLPE Maxm DC Stand. Packing

Nominal Cross Minimum Insulation Resistance of Length (m)
Item Sectional Area number of wires Thickness (mm) Conductor at
No. (mm2) in the conductor 20°C (Ω/km)
F-7 400 53 8.0 0.0470 500
F-8 500 53 8.0 0.0366 500
F-9 600 53 8.0 0.0283 500
F-10 800 53 8.0 0.0221 500

7. TECHNICAL SPECIFICATION OF JOINTING KITS FOR 33 KV XLPE,1-CORE,

COPPER CABLE
7.1. TERMINATION KITS (OUTDOOR)

Sl. No. Name of Item Termination jointing kits for 36 KV XLPE cable single-core,
(Outdoor)
1. Application For 33 KV, 1 core, XLPE, copper conductor armored cable
2. Installation Outdoor, mounted on Poles/Structure
3. System 33 KV, effectively grounded system
4. Cable Conductor As perTable-2 &material & price schedule.
5. Kit content Heat shrinkable high voltage insulating and non-tracking tubing
Heat shrinkable stress control tubing
Stress relieving mastic strip
Truck resistant sealant tape
Heat shrinkable track resistant rain skirt
Support Insulator
Cable preparation kit
Solder less earth connection kit
Compression lugs
Support Insulators Tee brackets
Installation Instructions

296
7.2 TERMINATION KITS (INDOOR)

Sl. No. Name of Item Termination jointing kits for 36 KV XLPE cable single-core
(Indoor)
1. Application For 33 KV, 1 core, XLPE, copper conductor armored cable
2. Installation For indoor switchgear terminations
3. System 33 KV, effectively grounded system
4. Cable Conductor As perTable-2 &material & price schedule.
5. Kit content Heat shrinkable high voltage insulating and non-tracking tubing
Heat shrinkable stress control tubing
Stress relieving mastic strip
Truck resistant sealant tape
Heat shrinkable track resistant rain skirt
Cable preparation kit
Solder less earth connection kit
Compression lugs
Installation Instructions
Note: The size & quantity of the termination kits shall be as per requirements to
connect the cables to the switchgear

297
 PUBLICATION 262-1988
BANGLADESH RURAL ELECTRIFICATION BOARD (BREB)
PEOPLES REPUBLIC OF BANGLADESH
STANDARD FOR
15 KV UNDERGROUND POWER CABLE
1. GENERAL

This standard establishes the physical and electrical requirements for 15 KV, 3-Core, copper
conductor, cross-linked polyethylene insulated power cable shall comply with IEC-60502. The
cable shall be suitable in all respect for use in 11 KV system, 50 hertz, underground distribution
system.

2. CLIMATE CONDITIONS

The working area is situated in a tropical climate and subject to monsoon conditions during July,
August and September each year. Wide spread river flood are to be expected.

a) Climate : Tropical, intense sunshine, heavy rain

and dust laden atmosphere.
b) Ambient air
temperature Extremities : 50 C to 450C
Ambient average : 250 C
annual Normal range : 250 C to 400C
Average in any one day does not exceed : 350 C
c) Average annual rainfall : 2850 mm.
d) Average relative humidities : 50 to 100 %
e) Maximum wind velocity : 160km/hour
f) Average isokeraunic : 80 days/year
g) Altitude : Sea level to 300 meters

3. REFERENCE DATA:

REB 15 KV, 3- core underground cable shall be comprised of the following:

3.1 CONDUCTOR

The conductor shall be stranded, circular and compacted copper wire in accordance with
IEC-228 or ASTM B3. The copper conducted cables shall be constructed with three cores in
size of as per table-2 or specified in material schedule. The cores in any one cable shall be
of equal cross-sectional areas.
3.2 CONDUCTOR SCREEN
The conductor screen shall comprise of a layer of extruded semi-conducting compound,
compatible in all respects with the conductor and insulation material. Conductor screen
shall be bonded to the insulation such a way that no voids or discontinuities are present. The
bond shall be adequate to withstand normal electrical and mechanical stresses in service
without degradation or separation.

Lapped semi-conducting tape shall not be used for conductor screens.

298
3.3 INSULATION

The insulation shall be cross-linked polyethylene (XLPE). The cable insulation shall be
extruded in one operation with conductor & insulation screens. The highest possible purity
of insulation material is required. The Bidder shall demonstrate that adequate precautions
are taken to remove contaminants and to eliminate the introduction of particles of
contaminate during material handling or the extrusion process.

The insulation material shall consist of cross-linked polyethylene tightly extruded over the
conductor screen. A cross-linking process using steam curing will not be permitted. Dry
process insulation shall be offered, without which the bid will not considered.

3.4 INSULATION THICKNESS

The minimum average thickness of insulation shall be (4.50 mm) for 15 KV underground
cable. The thickness at any point may, be less than the specified value, provided the
difference does not exceed 10 percent plus 0.1 mm.

The thickness of the semi conducting screens on the conductors and over the insulation shall
not be included in the measurement of insulation thickness.

3.5 INSULATION SCREEN

The insulation screen shall comprise of a non-metallic semi-conducting polyethylene part in

combination with a metallic part.

The non-metallic semi-conducting part shall be applied directly upon the insulation of each
core and shall comprise of a layer of extruded semi-conducting polyethylene compound.

The conductor screen, Insulation and semi-conducting part of Insulation screen layer shall
be applied to the conductor in common extrusion process with dry curing system.

The metallic part shall be stranded copper applied directly over the semi-conducting part.

3.6 INNER SHEATH AND FILLERS

The insulated and shielded power conductors shall be covered with PVC inner sheath.

3.7 ARMOUR

The armour shall consist of a single layer of galvanized steel wires.

The wire joints are brazed or welded and any wire shall be not less than 1 mm from nearest
joints in any other armour wire in the complete cable.

3.8 OVER SHEATH

The cable shall be sheathed overall with a PVC outer sheath. The outer sheath shall be of
smooth and uniform composition and free of holes, Cracks and blisters and imperfection.
As a protection against termite attack, the outer covering shall contain termite repellent
substance of Pb nephtanate.

299
 The outer sheath shall be of adequate strength and thickness to withstand the test voltages
and mechanical tests and shall be suitable for the ambient conditions at site.

The outer sheath material shall be capable of withstanding without damage or deformation
the highest temperature achieved with the cable at its rated current and at the site ambient
conditions.

3.9 MANUFACTURER’S IDENTIFICATION.

The manufacturer’s identification shall be printed with black colour on the identifying tape.
It shall show the rated voltage, conductor size, year of manufacturing and name of the
manufacturer at an interval of not more than 1000 mm throughout the length of the cable.

The designation of voltage and cable marking shall also be embossed on the outer PVC
covering.

The gap between the end of one set of embossed characters and the beginning of the next
shall be not greater than 150 mm throughout the length of cable with character
approximately 10 mm high. Each conductor shall be coded for phase identification.

Name of the Employer shall be embossed in the title- “BANGLADESH RURAL

ELECTRIFICATION BOARD (BREB)” at every 1000 mm gap.

3.10 CONTINUOUS CURRENT RATING:

The continuous rating of the cables that the bidder proposes to supply shall be calculated by
means of the procedure described in IEC publication 287 based on the site ambient
conditions including solar radiation, with the installation parameters as specified.

The maximum conductor temperature shall not exceed 900 C when carrying the rated
current under the most onerous site conditions.

The Contractor shall base his ratings on the site ambient conditions, with the methods of
installation and bonding as specified. Due account shall be taken of the heating due to other
cables or other sources of heat where these can be identified. TheContractor shall state all
the parameters including any assumptions that he has made in the calculation of continuous
current ratings.

3.11 SHORT CIRCUIT RATING:

All cables shall be capable of withstanding without damage or permanent distortion the
specified maximum short circuit currents for the specified times as under: -

The temperature of the conductors during the passage of the specified maximum fault
current for the specified time of one second shall not exceed 250 C for XLPE cables.

The cable design including the design of external Clamps or other restraining devices shall
be adequate to contain the mechanical forces arising from two or three phase short circuit
currents and longitudinal forces whether arising from magnetic effects or from thermal
expansion of conductors.

300
 The cable is suitable in all respect for use on an 11 kV system with a nominal 3-phase fault
level of 31.5 kA.

The cable metallic screen sheath and armor shall be capable of passing the specified
maximum earth fault current for the specified time of one second without damage,
permanent distortion or deterioration in the cable. The insulation screen shall be capable of
carrying an earth fault current of 31.5 kA for 1 second without damage. The short circuit
current should be as per IEC considering the cross section area of each phase.

If in order to comply with the requirement for carrying prospective earth fault current it is
necessary to rely on the armor and/ or sheath conductivity in addition to metallic core
screen tapes, the bedding material or materials shall be of the semi-conducting type.

4.0 TESTS:

4.1 GENERAL

The following tests shall be carried out to demonstrate the integrity of the cable.
The frequency of the alternating current supply is between 48 Hz and 62 Hz.

4.2 TESTS AT MANUFACTURER’S WORKS

Tests shall be carried out in accordance with the relevant British standards IEC publication
and the following type tests and routine tests shall be carried out at the Manufacturer’s
works.

a) TYPE TESTS

Type test for 15 KV cables shall be carried out in accordance with the IEC publication 540
and 60502for suitable length of cable.

I) ELECTRICAL TESTS

1. Partial Discharge test (s).

2. Bending test.
3. Heat cycle test.
4. Impulse Voltage withstand test
5. High voltage Alternating current test
II) NON-ELECTRICAL TEST
1. Measurement of Insulation thickness
2. Measurement of thickness of non-metalic sheath.
3. Determination of mechanical properties of insulation and sheaths before and
after aging.
4. Ageing test on pieces of complete cables.
5. Pressure test at high temperature on insulation &sheaths.
6. Hot set test.
7. Water absorption test on insulations.
8. Shrinkage test on XLPE insulation.
9. Electrical test after installation.
10. Water penetration test.

301
 b) ROUTINE TESTS:

The manufacturer shall carry out routine tests on all finished cables to demonstrate their
individual integrity as per IEC pub. 60502.
1. Measurement of Electrical Resistance of conductors.
2. High voltage test
3. Partial discharge test

4.3 SPECIAL TEST

Additional samples of cable shall be selected for special tests. The number and frequency of
special tests shall be in accordance with the procedures specified in IEC publication 60502.

The cable shall be subjected to the following special tests.

1. Conductor examination
2. Check of dimensions
3. Electrical test for cables
4. Hot set test.

5. PACKING

Cable shall be shipped on standard non-returnable steel drum, each drum having stenciled on its
side ; Size, Type, and length of cable, gross & net weight and contract number. The complete cable
drum shall be covered by steel sheet to protect from external thrust and the kits are to be export-
packed and properly protected for shipment, rough transportation and storage.

The maximum length of cable on a drum shall be as per table-2 with a variation of + / - 10% (ten
percent) and it shall be only one length of conductor on a reel.

Each kits cartoon shall be sealed in water proof polyethylene bag having a silicagel packet placed
inside the unit and then packed in polystyrene foam gasket closed by self adhesive tape. Size of the
items shall be marked by label on the foam for easy identification. Maximum 10 (ten) sets kits are
allowed to pack into separate wooden packing box lined with heavy gauge polyethylene.

6. DOCUMENTATION

Instructions to Bidders: The following test reports and the attached data schedule filled in
completely shall be included with offer, without which the offer shall not be considered for
evaluation.

a) All Routine Test, Type Test and Special Test reports as per clause 4.2a, 4.2b, 4.3 of
the specification and ISO-9001 Certificate of the identical 11KV cables from an
internationally recognized independent laboratory.

b) Supply record with documentary evidence of the identical 15 KV cables for last 5
(five) years mentioning Employer’s name, quantity, and year of supply.

c) Printed catalogue/Leaflet for the offered type of cables.

302
7. GENERAL REQUIREMENT OF 11 KV XLPE UNDERGROUND CABLE

Table-1

SL. No. Particulars Specified

1. INSTALLATION Direct burial
2. TYPE XLPE insulated, 3-core, armoured,
underground cable.
3. VOLTAGE:
a. Voltage between phases 11 KV
b. Maximum system voltage 15 KV
c. Rated voltage of cable U0/U 8.7/15 KV
4. CORES:
Number of cores Three core, stranded copper, round concentric.
5. CONDUCTOR:
a. Material copper
b. Design (stranded sectional round, compacted
etc.)
c. Strand As per table-2
d. Cross sectional area of each As per table-2 or specified in material schedule
conductor core
e. Maximum DC resistance of As per table-2
conductor at 200 C
6. CONDUCTOR SCREEN:
a. Material Extruded Semi-conducting PE
7. INSULATION:
a. Thickness (Nom) 4.50 mm
b. Type of curing Dry curing
8. INSULATION SHIELD Extruded Semi-conducting PE
9. METAL SHIELD Helically applied copper tape
10. INNET SHEATH Polyvinyl Chloride (PVC)
11. ARMOUR Galvanized steel wire.
12. OVER SHEATH PVC
13. STANDARDS Design, Manufacture, Testing & Performance
shall be in accordance to latest revision of IEC-
60502,540 or Equivalent International standard.

Table-2
Conductor XLPE m Stand.
Max DC.
Nominal Cross Minimum Insulation Resistance Short Circuit Packing
Item Sectional Area number of Thickness of Withstand Capacity Length
No. (mm2) wires in (mm) Conductor for 1 Second (m)
the at 20°C Phase Metalic
conductor (Ω/km) Conductoror Screen for
(KA) 1 Sec
(KA)

F-1 95 15 4.50 0.193 12.5 3 375-800

F-2 120 18 4.50 0..153 17 4 350-800
F-3 150 18 4.50 0..124 20 5 300-800
F-4 185 30 4.50 0.0991 25 6 300-800

303
8. TECHNICAL SPECIFICATION OF JOINTING KITS FOR 11 KV XLPE, 3-CORE,
COPPER CABLE

8.1. TERMINATION KITS (OUTDOOR)

Sl. No. Name of Item Termination jointing kits for 15 KV XLPE cable 3-core,
(Outdoor)
1. Application For 11 KV, 3- core, XLPE, copper conductor armored cable
2. Installation Outdoor, mounted on Poles/Structure
3. System 11 KV, effectively grounded system
4. Cable Conductor 185 mm2 copper conductor
5. Kit content Heat shrinkable high voltage insulating and non-
tracking tubing
Heat shrinkable stress control tubing
Stress relieving mastic strip
Truck resistant sealant tape
Heat shrinkable track resistant rain skirt
Support Insulator
Cable preparation kit
Solder less earth connection kit
Compression lugs
Support Insulators Tee brackets
Installation Instructions

8.2 TERMINATION KITS (INDOOR)

Sl. No. Name of Item Termination jointing kits for 15 KV XLPE cable 3-core
(Indoor)

1. Application For 11 KV, 3- core, XLPE, copper conductor armored cable

2. Installation For indoor switchgear terminations
3. System 11 KV, effectively grounded system
4. Cable Conductor 185 mm2 copper conductor
5. Kit content Heat shrinkable high voltage insulating and non-tracking
tubing
Heat shrinkable stress control tubing
Stress relieving mastic strip
Truck resistant sealant tape
Heat shrinkable track resistant rain skirt
Cable preparation kit
Solder less earth connection kit
Compression lugs
Installation Instructions

Note: The size & quantity of the termination kits and straight through joint splices shall be as per
as required to connect the cables to the switchgear and network.

304
 500 mm² 11 KV XLPE CABLE
Cross Link Polyethylene (XLPE) cables shall be suitable for operation at voltage of 11KV between
phases at continuous maximum conductor temperatures of 90 C. the cable shall be suitable in
all respect for use on 11KV system with a nominal three phase fault level of 31.5 KA. The cables
and associated fittings, joints and termination shall be so designed to prevent damage to the
cable or fittings, except in the immediate vicinity of the fault, in the event of an installation
failure at any point which results in a fault current to earth of 31.5KA for 3 sec.

Each core of Power cable shall comprise 500sq.mm. Copper Conductor XLPE Insulated, Copper
Screen and shall comply with IEC 60502, except as modified or extended by the requirement of the
specification. The length of cable on a drum shall be 500M continuous or as specified by the
Purchaser and it shall be shipped on standard non-returnable steel drum, each drum having
stencilled on its side; size, type and length of cable, together with its gross weight, net weight and
contract number.

1.1 CONDUCTORS

All conductor shall be stranded, circular and compacted and comply with IEC 228. Cables shall be
constructed with single core sizes of 500 mm2.

1.2 CONDUCTOR SCREENING

The conductor shall be screened with an extruded layer of semi-conducting material of 0.5mm
thickness for both the cables.

1.3 INSULATION

The insulation shall consist of cross-linked polyethylene tightly extruded over the conductor screen.
The insulation shall generally comply with IEC 502.

The highest possible purity of insulation material is required. The Bidder shall confirm that
adequate precautions are taken to remove contaminants and to eliminate the introduction of
particles of contaminants during material handling or extrusion process.

The Cable shall be manufactured through VCV/CCV.

The insulation material shall be cross-linked by a dry process. A cross-linking process using steam
curing will not be permitted.

1.4 INSULATION THICKNESS

The thickness of insulation shall be determined by taking the average of number of measurements
and shall be not less than the values tabulated in IEC Publication 502.

Insulation thickness shall not depart from the specified nominal value by an amount exceeding the
tolerances specified in IEC Publication 502.

The thickness at any point, if less than the specified value, provided the difference does not exceed
10 percent plus 0.1mm, may be acceptable.

305
The thickness of the semi conducting screens on the conductors and over the insulation shall not be
included in the measurement of insulation thickness.

1.5 INSULATION SCREENING

The insulation screen shall comprise a non-metalic semi-conducting polyethylene part in

combination with a metallic part.

The non-metalic semi-conducting part shall be applied directly upon insulation of the core and shall
comprise a layer of extruded semi-conducting polyethylene compound.

The conductor screen, insulation and semi-conducting part of insulation screen layer shall be
applied to the conductor in common extrusion process with dry curing system.

The metallic part shall be stranded copper applied over the layer of semi conducting compound.

There shall be a single layer of copper wires adequately spaced apart on each core of Power Cable.

The non-metallic part shall be applied directly upon the insulation and shall be a layer of extruded
semi-conducting compound. This screen shall be formed in such a way that it is readily removed
for jointing.

The insulation screen shall be capable of withstanding a fault current of 31.5KA for 3 sec. without
damage.

5.6 OVER SHEATH

The cable shall be sheathed overall with a Medium Density Polyethylene (MDPE) outer sheath.
The outer sheath shall be of smooth and uniform composition and free of holes, cracks, and
bisectors.

As a protection against termite attack, the outer covering shall contain the termite repellent
substance of Pb napthanate.

The outer sheath shall have adequate strength and thickness to withstand the test voltage and
mechanical tests and suitable for ambient conditions at site.

The outer sheath material shall be capable of withstanding the highest temperature achieved with
the cable at its rated current without damage or deformation at site ambient conditions.

The outer surface of the polyethylene outer sheath shall be as specified in IEC 60502.

1.7 ARMOUR

The armour shall consist of a single layer of galvanized steel wires in accordance with IEC 502.

The joints are brazed or welded and any wire shall be not less than 01 mm from the nearest joints in
any other armour wire in the complete cable.

306
1.8 CONTINUOUS CURRENT RATING

The continuous current rating of the cable shall be calculated in accordance with the procedure
described in IEC 60287 based on the site ambient condition, with the insulation parameters as
specified.

The cable current rating shall base on site ambient conditions, with the general methods of
installation and bonding.

The maximum conductor temperature shall not exceed 90 deg. C when carrying the rated current
under the most onerous site conditions.

1.9 SHORT CIRCUIT RATING

The cable shall be capable of withstanding the specified maximum short circuit current for the
specified times without damage or permanent distortion.

The temperature of the conductor at maximum fault current for the specified time shall not exceed
250°C as specified in IEC 60502.

1.10 MANUFACTURER IDENTIFICATION

The external surface of the cable shall be marked by the following at an interval of 1000 mm with
10mm high character throughout the length of the cable:

(i) “11KV, XLPE, 1-Core, 500 sq.mm Cu”

(ii) “BREB”, “Manufacturers Name”

2.0 GENERAL TECHNICAL REQUIREMENT OF 11KV XLPE 500 MM2 COPPER

CABLE

Item
Description of Items Unit Particulars
No.
1 System Voltage KV 11
2 Rated Voltage KV 6/10(12)
3 Cross sectional Area of mm2 500
Conductors
4 Insulation thickness mm Average thickness shall not be less than 3.40
mm nominal value as per IEC 502.
However, thickness at any point may be less
than nominal value provided that the
difference does not exceed 0.1mm + 10% of
nominal value.
5 Manufacturing process Manufactured through VCV/CCV.
6 Conductor Material Copper
7 Shape of Conductor Compact Circular
8 Type of Conductor Screen Semi-conducting XLPE
9 Conductor Temperature at °C 250
end of short Circuit

307
 2.1 STRAIGHT-THROUGH JOINT BOX FOR 11KV XLPE, 1-CORE, 500 MM2
COPPER CABLE

Item
Description of Items Particulars
No.
1 Application For 11KV, 1-core, XLPE 500 mm2 Copper
Conductors
2 Installation For underground horizontal mounting
3 System 11KV, effectively earthed system
4 Cable conductor 500 mm2 1-core, Copper Conductors
5 Construction The joint shall be proof against ingress of moisture
and water
6 Kit content - Compression ferrules
- Valid filling tape
- Heat shrinkable stress control tubing
- Truck resistant sealant tape
- Heat shrinkable high voltage insulating tape
- Heat shrinkable black/red dual wall
- Estomeric tube
- Roll spring
- Heat shrinkable outer jacket tube
- Cable preparation kit
- Solderless earth connection kit
- Misc. other material
- Installation instructions

2.2 INDOOR TERMINATION KITS FOR 11KV, XLPE, 1-CORE,500 MM2 COPPER
CABLE

Item Description of
Particulars
No. Items
1 Application For 11KV, 1-core, XLPE 500 mm2 Copper Conductors
2 Installation For Indoor switchgear terminations
3 System 11KV, effectively earthed system
4 Cable conductor 500 mm2 1-core, Copper Conductors
5 Kit content - Heat shrinkable high voltage insulating and non-tracking
tubing
- Heat shrinkable stress control tubing
- Stress relieving mastic strip
- Truck resistant sealant tape
- Cable preparation kit
- Solder less earth connection kit
- Compression lugs for 500 mm2 Copper Conductors
- Installation instructions

308
2.3 OUTDOOR TERMINATION KITS FOR 11KV, XLPE, 1-CORE, 500 MM2 COPPER
CABLE

Item Description of
Particulars
No. Items
1 Application For 11KV, 1-core, XLPE 500 mm2 Copper Conductors
2 Installation For outdoor installation on poles/structures
3 System 11KV, effectively earthed system
4 Cable conductor 500 mm2 1-core Copper Conductors
5 Kit content - Heat shrinkable high voltage insulating and non-tracking
tubing
- Heat shrinkable stress control tubing
- Stress relieving mastic strip
- Truck resistant sealant tape
- Heat shrinkable truck resistant rain skirt
- Support insulator
- Cable preparation kit
- Solder less earth connection kit
- Compression lugs for 500 mm2 Copper Conductors
- Support insulators Tee Brackets
- Installation instructions

309
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 11KV, 1-CORE X 500 SQ. MM U/G XLPE COPPER CABLE
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be rejected) Failure
to provide all of the information requested may lead to the rejection of the tender.
Supplier’s /
Sl. Description of Items Unit Required
Manufacturer’s
No. Specification
Particulars
1 Name & address of the
Manufacturer
2 Type/Model of the offered
Cable
3 System Voltage KV 11
4 Rated Voltage of Cable KV 6/10 (12)
5 Process of manufacturing VCV/CCV.
6 Number of core and Cross Sq.mm 1X500
sectional area of conductor
cores
7 Conductor materials Copper
8 Shape of conductor Round
9 Type of conductor screen Semi-conducting
10 Thickness of semi- mm 0.6
conducting screen
11 Average thickness of mm 3.4
insulation
12 Process of curing Dry process
13 Cross Linked
Material of Insulation
Polyethylene (XLPE)
14 Type of non-metallic Semi-conducting
insulating screen
15 Thickness of semi- mm 1.0
conducting insulation screen
16 Number and diameter of No./mm Based on design
copper screen strands calculation
17 Composition of filler PVC
18 Composition of bedding Extruded PVC
19 mm Based on design
Thickness of bedding
calculation
20 Number and diameter of No./mm As per IEC 60502
armour wire
21 Average thickness of PVC mm Based on design
over sheath calculation
22 Nominal diameter of mm Based on design
complete cable calculation
23 Nominal weight per meter of Kg/m Based on design
complete cable calculation
24 Minimum radius of bend mm Based on design
round which cable can be calculation
laid
25 Maximum D.C. resistance of Ohm/m Based on design
conductor per meter at 20°C calculation

310
 Supplier’s /
Sl. Description of Items Required
Unit Manufacturer’s
No. Specification
Particulars
26 Maximum A.C. resistance of Ohm/m Based on design
conductor per meter at a calculation
maximum conductor
temperature
27 Star reactance per meter of Ohm/m Based on design
cable at 50Hz calculation
28 Star capacitance per meter of pF/m Based on design
cable at 50Hz calculation
29 Charging current per mA Based on design
conductor per meter at calculation
6300/11000 Volts, 50Hz
30 Maximum current carrying A Based on design
capacity of conductor in calculation
ground
31 Maximum conductor °C Based on design
temperature under continuous calculation
loading
32 Short circuit capacity of the KA 70
cable for 1sec. duration
33 Conductor temperature at the °C ≤250
end of short circuit
35 Screen short circuit KA 25
withstand capacity for 1sec.
36 duration
Armour short circuit KA Based on design
capacity calculation
37 Cable resistance, reactance:
a) for positive sequence Ohm/km Based on design
calculation
b) negative sequence Ohm/km Based on design
calculation
c) zero sequence Ohm/km Based on design
calculation

311
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE

FOR JOINING KITS FOR 11 KV XLPE , 1-CORE, 500 MM2 COPPER CABLE
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be
rejected)
Failure to provide all of the information requested may lead to the rejection of the
tender.
Item Description of Required Particulars Manufacturers
Sl. Items Particulars
No.
Indoor Termination Kits for 11KV XLPE, 1-Core, 500 mm2 Copper cable
1 Name and address of Shall be furnished
the manufacturer
2 Type/model of the Shall be furnished
kits
3 Application For 11KV, 1-core, XLPE 500 mm2
Copper Conductors
4 Installation For Indoor installation in switchgear
terminations
5 System 11KV, effectively earthed system
6 Cable conductor 500 mm2 1-core Copper Conductors
7 Kit content - Heat shrinkable high voltage
insulating and non-tracking
tubing
- Heat shrinkable stress control
tubing
- Stress relieving mastic strip
- Truck resistant sealant tape
- Cable preparation kit
- Solder less earth connection kit
- Compression lugs for 500 mm2
Copper Conductors
- Installation instructions
Outdoor Termination Kits for 11KV XLPE, 1-Core, 500 mm2 Copper cable
1 Name and address of Shall be furnished
the manufacturer
2 Type/model of the Shall be furnished
kits
3 Application For 11KV, 1-core, XLPE 500 mm2
Copper Conductors
4 Installation For Outdoor installation on
poles/structures
5 System 11KV, effectively earthed system
6 Cable conductor 500 mm2 1-core Copper Conductors
7 Kit content - Heat shrinkable high voltage
insulating and non-tracking
tubing
- Heat shrinkable stress control
tubing
- Stress relieving mastic strip
- Truck resistant sealant tape
- Heat shrinkable truck resistant
rain skirt
- Support insulator
312
Item Description of Required Particulars Manufacturers
Sl. Items Particulars
No.
- Cable preparation kit
- Solder less earth connection kit
- Compression lugs for 500 mm2
Copper Conductors
- Support insulators Tee Brackets
- Installation instructions
Straight-through joint box for 11KV XLPE, 1-Core, 500 mm2 Copper cable
1 Name and address of Shall be furnished
the manufacturer
2 Type/model of the Shall be furnished
kits
3 Application For 11KV, 1-core, XLPE 500 mm2
Copper Conductors
4 Installation For underground horizontal
mounting
5 System 11KV, effectively earthed system
6 Cable conductor 500 mm2 1-core Copper Conductors
7 Construction The joint shall be proof against
ingress of moisture and water
8 Kit content - Compression ferrules
- Valid filling tape
- Heat shrinkable stress control
tubing
- Truck resistant sealant tape
- Heat shrinkable high voltage
insulating tape
- Heat shrinkable black/red dual
wall
- Estomeric tube
- Roll spring
- Heat shrinkable outer jacket tube
- Cable preparation kit
- Solder less earth connection kit
- Misc. other material
- Installation instructions

313
 CONDUCTORS AND CONNECTIONS

Overhead conductors carried by the switchyard structures shall be erected with such sags and
tensions that when the conductors are subjected to load combinations, the factor of safety will not
be less than 3.5.
Materials used for connections shall be stressed to not more than forty percent of their elastic limit.
Provision shall be made for expansion and contraction with variation in conductor temperature and
bus bars shall be arranged so they may be readily extended in length with a minimum of
disturbance to existing equipment. The design of joints and connections shall be such as to permit
ready dismantling.
Connectors shall be of an approved type. Connections dependent upon site welding techniques will
not be permitted.

All bus connections and joints for aluminum conductor where applicable shall be of crimp and
bolted palm types in accordance with the design parameters and the general technical requirements
of this specification and the relevant standards.
Suspension and tension conductor clamps shall be of approved types and shall be as light as
possible. Suspension and tension clamps shall be designed to avoid any possibility of deforming the
stranded conductor and separating the individual strands.
Tension conductor clamps shall not permit slipping of, or damage to, or failure of the complete
conductor or any part thereof at a load less than 95 percent of the ultimate strength of the conductor
as stated in the schedule of particulars and guarantees.
All clamps and fittings and their components shall be electro-chemically compatible with the
conductor material and those made of steel or malleable iron shall be hot dip galvanized. All bolts
and nuts shall be locked in an approved manner.
Unless otherwise approved, connections shall be so arranged and supported that under no
circumstances, including short circuit conditions, can the clearances between live metal and earth of
earthed metal work or between other conductors be less than the specified distances.
Where dissimilar metals are in contact, approved means shall be provided to prevent electro-
chemical action and corrosion. Unless otherwise approved, joints and surfaces of copper or copper
alloy fittings shall be tinned.
Cleaning down and preparation of contact surfaces of connectors and clamps shall be to the
approval of the Project Manager.

314
 DISCONNECTORS AND EARTHING SWITCHES
1. GENERAL

Disconnecting and earthing devices shall be in accordance with IEC 60129 and IEC 60265 (Part 2).
Transformer disconnectors in transformer circuits without circuit breakers on the High Voltage side
shall be in accordance with IEC 60265 and shall be capable of breaking the transformer
magnetizing current. All shall be complete with supporting steel work and installed to permit
maintenance of any section of the substation plant when the remainder is alive and shall be so
locate that the minimum safety clearances stated in BS 7354 are always maintained.

In outdoor substations, disconnectors shall preferably be of the single throw double air break,
centre rotating post type or the double rotating post type with single air break and shall be to the
approval of the Project Manager. Pantograph designs, or other alternatives, if applicable will be
considered.

Disconnectors shall comply with the requirement of BS 5253 in respect of lighting impulse voltage
tests. The contact resistance should be ≤ 30µΩ

Circuit isolating switches shall be rated not less than specified. Bus section/coupler isolating
switches shall be rated not less than the associated bus bars.

Isolating switches shall generally be designed of live operations and will not require switching
current other than the charging current of open bus bars and connections or load currents shunted
by parallel circuits. Main contacts shall be of the high pressures line type and arcing contacts, if
provided, shall be to the Project Manager approval.

Service conditions require that isolating switches shall remain alive and in continuous service for
periods of up to 2 (Two) years in the climatic conditions specified and without operation or
maintenance. The contacts shall carry their rated load and short circuit currents without overheating
or welding and at the end of the two year period the maximum torque required at the operating
handle to open a 3-phase disconnector shall not exceed 340 Nm.

All feeder disconnectors and high level disconnectors where specified shall be fitted with approved
three phase line earthing devices, mechanically coupled or interlocked with the main isolator, so
that the earthing device and main isolator cannot be closed at the same time.

The earthing switch, when in the closed position, shall be capable of carrying the rated short time
current for three seconds without the contacts burning or welding.

Isolating devices shall be interlocked with circuit breakers and as necessary to prevent the
possibility of making or breaking load current. Except where electrical interlocking is provided
each mechanism box shall accommodate the relevant Castell type key interlocks.

Disconnector operation mechanisms shall be robust construction, carefully fitted to ensure free
action and action and shall be unaffected by the climatic conditions at site. Mechanisms shall be as
simple as possible and comprise a minimum of bearing and wearing parts. Approved grease
lubricating devices shall be fitted to all principal bearing which are not of the self lubrication type.
The mechanisms shall be housed in a weatherproof enclosure complete with auxiliary switches,
terminal blocks and cable gland plates. All steel and malleable iron parts, including the supporting
steelwork shall be hot dip galvanized.

315
2. 33 KV ISOLATOR, EARTH SWITCH AND FUSE SWITCH

(a) 33 KV Isolator, Off Load Type (Outdoor)

The 33 KV Isolator, shall be a gang operated type, horizontal mounted and horizontal break, 3-
phase, outdoor mounted, manual operating type along with the following feature:
(a) Auxiliary contact operative through the operating mechanism of the isolator blade (6
normally ON and 6 normally OFF contacts).
(b) Terminal connecting clamp suitable for being connected with AAAC/ ACSR conductor.
(c) Earth pad for safety of the operating person. The operating lever shall be provided with
locking device. Necessary grounding points shall be provided with connector suitable for
being connected with 100 mm2 stranded Cu wire.
(d) Gland for multi core control cable.
(e) 33 KV structure beam, complete operating mechanism for easy manual operation from
the ground and grounding points with connection clamps for connecting with str. Cu wire.
(f) All ferrous parts to be hot dip galvanized as per BS 729.
(g) All electrical auxiliaries to be housed in a fully weather proof housing.
All other features as stated in the table of guaranteed data schedule should be applicable also.
(b) 33 KV Isolator with Earth Switch of the Line Side (Outdoor)
Same as in specification of 33 KV isolator but with the added feature of earthing blade with will
also hand operable from the switchyard by another handle and the operation of this earth blade with
be mechanically interlocked with that of the main blade. The earth blade will be of same current
rating as the main blades and shall be earthed through a 100 mm sq. (cu) earthing conductor.
Necessary aux. contracts for position indication and to provide electrical inter locking should be
there.

(c) 33KV Fuse Switch with Holder and Fuse (Outdoor) for By-passing VCB and CT

The 33 KV Fuse Switch, shall be 3 pole double-break gang operated type, outdoor vertical
mounted, manual operating type which shall have a removable fuse in series. The switch shall be
suitable for mounting on a pole (wooden, concrete or metal). A suitable structure shall be
constructed by the Contractor with proper phase & ground clearances.

The circuit breaker/by-pass switch combination shall be designed in such a way that the circuit
breaker primary circuits can be isolated by bolted links or switchable single phase links or similar
disconnect devices to enable maintenance of the CB with the by-pass switch closed supplying the
substation, without encroaching on any safety clearances.

The purpose of the fused bypass switch is to enable the substation to be supplied while the circuit
breaker/current transformer combination is being maintained or replaced. The Contractor shall
design and install 2 sets of disconnect links in the circuit breaker/current transformer branch of the
circuit so that the complete breaker/current transformer can be safely maintained with the bypass
switch closed and providing 33 KV supply to the power transformer.
3. 11 KV ISOLATOR

The 11KV Isolator, shall be of gang operated type, horizontal mounted and horizontal break, 3
phase, outdoor mounded, manual operated type.

316
 INSULATORS

1. DESIGN

For open terminal type insulator, transformer terminal bushings and cable sealing ends the
minimum specified creepage distance measured from the insulator metal cap to the base over the
insulation cells shall not be less than 25mm per KV of rated voltage between phases.

All types of insulator shall satisfactorily withstand the specified climatic and service conditions.
The strength of insulators as given by the electro-mechanical test load shall be such that the factor
of safety, when supporting their maximum working loads, shall be not less than 2.5.

Designs shall be such that stresses due to expansion and contraction in any part of the insulators
and fittings do not lead to development of defects.

All insulators shall be manufactured in one piece. Jointing of solid or hollow porcelains in not
permitted except by use of metal fittings.

Damaged insulators may not be repaired without the written consent of the Project Manager.

Arcing horns are not required on post type and string insulators.

All insulators shall be porcelain construction type in accordance with IEC 60305. Post insulators
shall comply with IEC 60273. Porcelain shall be sound, free from defects and thoroughly vitrified
and the glaze shall not be depended upon for insulation.

The minimum specific creepage distances of outdoor insulators shall be as stated in the schedule of
requirements. The shed shape, spacing and inclination shall be such as to with stand moderate
pollution and the extremely heavy rainfall encountered at Site.

Glaze shall be smooth, hard of a uniform shade of brown and shall completely cover all exposed
parts of the insulators. Outdoor insulator fittings shall remain unaffected by atmospheric conditions
producing weathering, acids alkalis, dust and rapid changes in temperature that may be experienced
under working conditions.

Porcelain insulators shall be secured in an approved manner, preferably by means of bolts or metal
clamping plates with suitable packing material interposed.

Porcelain shall not engage directly with hard metal and where necessary, approved water and oil
resistant yielding material shall be interposed between the porcelain and fittings. All porcelain
clamping surfaces shall be approved quality applied in an approved manner and shall not be
chemically active with the metal parts or cause fracture by expansion in service. Where cement is
used as a fixing medium, the cement thickness shall be as small and as even as possible and care
shall be taken to correctly centre and locate the individual parts during cementing.
Suspension and tension insulators shall comprise porcelain units with ball and socket fittings. Each
tension insulator shall consist of a string of insulator units and the ball socket joints of the units and
of the associated fittings shall be in accordance with IEC 60305 (BS 137 Part 2) and IEC 60383
(BS Part 1).
Retaining pins or locking devices for cap and pin insulators shall be in accordance with BS 137.

317
Unless otherwise approved, the individual units of both the suspension and tension insulators sets
shall be identical and interchangeable.

2. IDENTIFICATION

Each insulator shall have marked on it the manufacture’s name or trademark, the year of
manufacture and the insulator reference. Tension and suspension insulators shall also be marked
with the guaranteed electro-mechanical strength. Marks shall be visible after assembly of fittings
and shall be imprinted and not impressed. For porcelain insulators, the marks shall be imprinted
before firing and shall be clearly legible after firing and glazing.

When a batch of insulators has been rejected, no further insulators from this batch shall be
submitted and the Contractor shall take adequate steps to mark or segregate the insulators
constituting the rejected batch in such a way there is no possibility of the insulators being
subsequently resubmitted for tests or supplied for the Employer’s use.

318
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 33 KV ISOLATOR/EARTH SWITCH
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be
rejected) Failure to provide all of the information requested may lead to the rejection of
the tender.

BREB/PBS Tenderer’s
Description Unit
Requirement Guaranteed Values
1. Name of the manufacturer Required
2. Switch Type & Model Required
3. Rated Voltage & Frequency KV/H 33,50
z
4. Maximum KV 36
Continuous voltage
5. Rated Current A 2500/2000/1250
6. Rated Short time current (3 sec) KA 31.5
7. Impulse withstand voltage KV 170
8. Power Frequency withstand voltage KV 70
(1 min)
9. Creepage Distance mm Required
10. Dimension of the supporting Required
steel structure
Height mm Required
Width Mm Required
Length Required
11. Weight of the phase units Kg Required
12. Phase center distance Mm Required
13. Period of time, equipment has Years 2
been in service
14. Period of time, equipment has Years 5
been in manufacture
15. Earth Switch Required
16. Manufacturer Required
17. Country of Manufacture Required
18. Manufacturer type designation Required
19. Reference Standard Required
20. Number of years disconnector type in Required
service
21. Nominal system Voltage KV 33
22. Highest system voltage KV 36
23. Frequency Hz 50
24. Rated Current A 2000/1250
25. Type of operating mechanism Hand
26. Contact resistance μ ≤ 30

319
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
FOR 11 KV ISOLATOR
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be
rejected)
Failure to provide all of the information requested may lead to the rejection of the
tender.

BREB/PBS Tenderer’s
Description Unit
Requirement Guaranteed Values
1. Name of the manufacturer Required
2. Switch Type & Model Required
3. Rated Voltage & Frequency KV/H
11, 50
z
4. Maximum Continuous voltage Kv 12
5. Rated Current A 1250
6. Rated Short time current (3 sec) KA 31.5
7. Impulse withstand voltage KV 75
8. Power Frequency withstand voltage (1
KV 28
min)
9. Creepage Distance mm Required
10. Dimension of the supporting steel
Required
structure
Height mm Required
Width mm Required
Length Required
11. Weight of the phase units Kg Required
12. Phase center distance mm Required
13. Period of time, equipment has been in
Years 2
service
14. Period of time, equipment has been in
Years 5
manufacture
15. Contact resistance μ ≤ 30

320
 TECHNICAL REQUIREMENT AND GUARANTEE SCHEDULE
For 33KV, DOUBLE BREAK SWITCHED FUSE
(To be filled up by the tenderer with appropriate data, otherwise the Tender will be
rejected) Failure to provide all of the information requested may lead to the rejection of
the tender.

Description Unit REB Tenderers

Requiremen guaranteed values
1. Name of the manufacturer Required
t
2. Switch Type & Model Dual
Required
Break
3. Rated Voltage & Frequency KV/Hz 33,50
4. Maximum Continuous voltage Kv 36
5. Rated Current A 630
6. Rated Short time current (3 sec) KA 31.5
7. Impulse withstand voltage KV 170
8. Power Frequency withstand voltage (1
KV 70
min)
9. Fuse Type Required
10. Fuse Rating A 630
11. Creepage Distance mm Required
12. Dimension of the supporting steel structure Required
Height mm Required
Width mm Required
Length mm Required
13. Weight of the phase units Kg Required
14. Phase center distance mm Required
15. Period of time, equipment has been in
Years 2
service
16. Period of time, equipment has been in
Years 5
manufacture

321
 SUBSTATION EARTHING SYSTEM
1. GENERAL

Circuit breakers, power transformers, voltage transformers, auxiliary transformers, earthing

switches and other electrical apparatus shall each be connected to the main earth bus by means of a
separate subsidiary connection. Gradient control mats shall be installed adjacent to each circuit
breaker and disconnect switch mechanism box. Each mat shall be connected directly to the earth
grid and the equipment.

Isolating supports, bus bar supports and cable sheaths may be earthed in groups by a separate
branch connection from each item of equipment in the group the branch connections being
connected by a single subsidiary connection to the main earth. Isolating and earth switch
mechanism boxes shall be earthed by a connection separate from that effecting the earthing of the
associated switch.

The main members of the steel structures shall be earthed by continuous copper connections
bonded to the steelwork and these connections shall be connected separately at each column to the
main or subsidiary earth. There shall be 2 connections to each structure and 1 to each piece of high
voltage apparatus.

Connections to apparatus and structures shall be made clear of ground level, preferably to a vertical
face and protected against electrolytic corrosion.

Current transformer and voltage transformer secondary circuits shall be complete and shall be
earthed at one point only (at the control building) through links situated in an accessible position.
Each separate circuit shall be earthed through a separate link, suitably labelled. The links shall be of
the bolted type, having necessary provision for attaching test leads.

The earth system shall be designed so as to include all overhead line terminal Poles, by bonding the
overhead earth wire to the earth grid by means of a link which shall be capable of being removed
for testing purposes.

The terminal pole shall also be included within the boundary of the earth grid by extending the grid
if necessary.

Structures and masts for lighting and security surveillance equipment shall also be within the
perimeter of the earth grid. No fixed low voltage equipment, with the exception of a warning or
alarm button and intruder alarms, which shall be of the double insulation type, shall be erected
outside the perimeter of the earth grid.

All control and relay panels shall have a continuous earth bus run of sectional area approved by the
Project Manager along the bottom of the panels, each end being connected to the main earthing
system. Metal cases of instruments and metal bases of relays on the panels shall be connected to
this bar by conductors of sectional area approved by the Project Manager.

Loops shall be provided on the earthing system in positions approved by the Project Manage, for
the attachment of portable earth connectors during maintenance. These will normally be in the earth
bar run between the equipment and the base of the structure. They shall be formed separately from
the bar and soldered or thermo-welded thereto. Where necessary, rods shall be provided at the tops
of bushings or insulators for the attachment of portable earth clips.

322
Earthing for any high frequency coupling equipment , if applicable, and surge diverters shall be via
a copper rod driven directly into the ground at a position immediately adjacent to the equipment
being earthed in addition to the normal earth connection.

2. EARTHING SYSTEM DESIGN

The earthing system shall be designed to meet the requirements of this specification and shall be in
accordance with "The Guide for Safety in Alternating Current Substation Grounding" as published
by the Institute of Electrical and Electronic Engineers Incorporated, Publication IEEE 80 and 142.
The Contractor shall present calculations to show the earthing system meets these requirements and
can be shown to be safe in terms of touch, step and transferred potentials. The earth resistance
should be kept below or equal to 0.2 Ω.

Electrical measurements of the subsoil at various depths, up to 20 metres shall be made at the site
of the substation in order to determine the layered effects of the ground from which the effective
ground resistivity and hence the expected resistance of the proposed earth grid system may be
predicted.

Soil composition may be highly corrosive and special consideration shall be given to this problem.
The earth grid shall be effectively protected against corrosion. Cathodic protection, if considered,
may adversely affect other equipment and shall be subject to approval by the Project Manager.

In actual design, the earthing system shall take the form of a combination of grids of buried
conductors and earth rods driven vertically into the ground. Within the grid, conductors shall be
laid in parallel lines at reasonably uniform spacing. They shall be located along rows of structures
or equipment to facilitate the making of earth connections, where practical.

The main earth and each subsidiary earth shall have a sectional area, as required for 31.5 kA for 3
sec, in any case not less than 120 mm2 in any part of its length. Each branch connection shall have a
sectional area of not less than 70 mm2.

Connections to the grid of all non-current carrying metallic parts, which might become energised
by chance, such as metal structures, building earth, equipment, earth rods, water pipes, etc. shall not
be less than 70 mm2 and shall be of adequate size, current-carrying capacity and mechanical
ruggedness.

The spacing between conductors forming the mesh system shall be such as to limit the grid
potential rise to a value that limits the touch voltage to a value not greater than the maximum
tolerable touch potential assuming a fault clearance time equal to that of the main protection
equipment being provided.

Each group of earth conductor shall be connected to the main earth grid through connections
having a sectional area of not less than 120 mm2 which shall be protected from corrosion.
The grid shall be subdivided into a number of sections, interconnected with test links. These links
shall be accessible from above-ground.

Areas of the grid, where high concentrations of fault currents can appear, as at neutral earthing
connections, shall have reinforced conductor sizes where necessary, to handle adequately the
highest fault current and its duration.
In case the equipment is widely spaced in the station, individual local grids may be established at
the various equipment locations and the local grids shall be interconnected and connected to the

323
overall earth grid. Interconnecting conductors shall not be less than the size of the conductor for
main grid.

Metal parts of all equipment, other than those forming part of an electrical circuit shall be
connected directly to the main earth system via a single conductor. The arrangement of the mesh
earth system shall be such as to minimise the length of these single connections.
Earth bars installed directly into the ground should normally be laid bare and the trench back-filled
with fine topsoil. Where the soil is of a corrosive nature, precautions must be taken to protect the
earth bar.

All trenches shall be backfilled in compacted 100 mm layers. All stones and other sharp objects
shall be removed from the backfill by a suitable sieve.

Copper to copper joints on strip conductor shall be brazed, using zinc-free brazing material with a
melting point of not less than 600°C, or by approved exothermic welding. All exposed joints shall
be at a minimum height of 150 mm above floor or ground level. Earth conductor joints that are
required to be broken for testing or maintenance shall have mating surfaces tinned.

After installation of the earth system the Contractor shall measure the resistance of the substation.
The method used shall preferably be the "fall of potential" method, requiring the availability of a
local low voltage supply but other methods using an earth resistance megger will be acceptable in
the event of a local supply being unavailable.

In the case of surge (lightning) arrestors a local earth connection shall be made by driving
electrodes into the earth near the arrestors and the lightning arrester earth conductor shall be
connected to both the rod and to the common earthing grid of the station. The connection from
arrester to earth shall be as short and as straight as possible. The conductor shall not be less than
120 mm2.

The measured earth resistance shall not exceed 0.5 ohm. A value higher than 0.5 ohm shall be
subject to the approval of the Project Manager. The resistance shall be measured with all
transmission line earth wires connected to the earthing grid.

In the event of the substation resistance obtained with the foregoing installation being of a
magnitude unacceptable to the Project Manager, then where practicable, the ground area enclosed
by the earth system shall be increased by installing directly in the ground an additional copper
conductor in the form of a ring around the site, or by additional conductors within the site.
Alternatively earth conductors can be directly buried radially outside the substation perimeter
fence. The use of earth plates as current carrying electrodes is not acceptable. Any additional
conductors shall be as directed by the Project Manager.

From the point of view of the possible damage to apparatus, the earthing system shall be such as to
limit voltage appearing between the substation equipment and the main body of earth, so that
insulation breakdown or burning does not occur on apparatus. For the same reason, voltage rise
between earthed points in the substation shall be kept to a minimum. In addition, the effectiveness
of any surge protection devices shall be fully realized by providing an adequate earth path. In this
case, the earthing system shall not only be of low resistance, but of as low reactance as practicable.

N.B: For the earthing system design copper conductor shall be considered instead of copper earth
electrode.

324
3. STEP AND TOUCH VOLTAGE

The earthing systems shall be so designed as to keep the "step" and "touch" potentials within
acceptable limits, thereby ensuring safety to the personnel. The aim shall be to ensure that under
either normal or abnormal conditions no dangerous voltages can appear on the equipment or
accessories to which a person has legitimate access.

The step and touch potential voltages obtained inside the site and at selected locations around the
fence/gate shall also be measured by a suitable method acceptable to the Project Manager.
Appropriate measures shall be taken to rectify the causes of any deviations from allowable values.

4. FENCE AND PERIMETER EARTHING

The fence surrounding the substation shall be earthed to its own earth grid and the fence earth grid
shall be connected to the main station earth grid at frequent intervals as approved by the Project
Manager.

A continuous conductor shall be laid outside the periphery of the substation site at a distance of
1.0 metre from the boundary fence and at a depth of 0.6 metres below the surface. This shall be
welded to earth rods installed at adequate intervals and at points adjacent to each corner and
immediately below any overhead line entering or leaving the site. The location of the mesh
conductors shall be such as to enable all items of equipment to be connected to the earth system via
the shortest possible route. All corner fence posts and posts adjacent to earth rods shall be
effectively connected to the earth conductor.

Gateposts forming part of the substation fence shall be bonded together with below ground
connections and the gates themselves shall be electrically bonded to the posts.

The alternative approach of independently earthing the fence and placing it outside the earth grid
area shall only be adopted if the above mentioned procedures prove insufficient or impracticable.
The Contractor shall provide calculations to show that this approach produces safe touch voltages
at the fence and shall ensure that the fence is isolated from all other buried metalwork.

5. TESTS

All relevant type and routine tests shall be carried out.

Complete charge and discharge tests on each of the combined batteries and chargers shall be
conducted and results recorded so as to permit verification of the ampere-hour capacity of the
battery. During these tests the Project Manager shall select at random reference cells and the
voltage curves thereof shall be checked when the battery is discharged over three and ten hour
periods. The alarm levels and the automatic voltage control feature of the charger shall be
demonstrated over the specified load range.

325
 SUBSTATION BATTERY AND BATTERY CHARGER
The following battery size is the minimum expected and is provided as a guide only. The
Contractor shall provide the detailed calculations of the loads and the expected loadings and the
sizing of the battery for approval before implementation. The number of cells required in the
battery shall be determined by the Contractor in accordance with the design of the DC
requirements.

A. BATTERY

i Application : Supply for remote control, operation, indication,

protective and regulation apparatus, emergency light
etc.
ii Installation : Indoor (self-supporting unit).
iii Type/Model : Nickel Cadmium Alkaline
iv Operating Voltage : 110 V, DC
v Continuous discharge : 50 A during 5 hour
vi Capacity (at the 5 hr rate) : 250 A hour
vii No. of cell : 92
viii Discharging voltage : 1.3 - 1.5 volt per cell
ix Charging voltage (normal) : 1.45 - 1.55 volt per
cell : 1.65 volts per cell
x Charging voltage (max)
: Transparent plastic :
xi Type of container
xii Mounting Cabinet
xiii Construction : Closed top
xiv Standard : All equipment and materials shall be designed,
manufactured and tested in accordance with the latest
editions of applicable IEC standard unless otherwise
specified in the specification. Other internationally
acceptable standards will also be considered provided
that relevant values are at least similar to those under
IEC standards.

326
Features and Accessories:
The battery shall be Nickel Cadmium Alkaline type, negative plates shall have life equal to or
greater than positive plates.

The battery shall have built in protection against active materials shedding and grid corrosion and
shall be assembled in heat-resistant, shock-absorbing containers. The containers and covers shall be
connected together to form a leak proof bond against seepage of electrolyte.

The cell terminal posts of the inter-cell and end cell connectors shall have adequate current carrying
capacity and shall be of lead alloy or lead alloy reinforced with copper inserter. The container shall
be filled with sufficient quantity of Alkaline complying with internationally acceptable standards to
ensure that the surface of Alkali is leveled with the level mark.
Cells shall be equipped with necessary bolts and alkali resisting units, shall be furnished with all
the bolts.
Plates shall be hung suspended without touching the bottom of the containers. Containers shall
provide sufficient sediment space so that the plates in the cell, as well as to avoid cleaning of cells
during the expected life of the battery.
110% of the required electrolyte meeting the manufacturer’s specification shall be supplied at the
correct filling specific gravity with each battery. The electrolyte shall be packaged in 15 gallons or
less plastic coated steel drum or in plastic containers. After discharging off the specified rated
capacity, the battery shall have the voltage including the internal resistance drip of all inter cell and
inter rack connectors not to drop below 1.10 VPC.

The battery rack shall be a few step structural steel and shall be printed with 2 coats of acid
resistant Grey paint. Inter rack connector terminal lugs shall be provided with each rack.
Battery shall be shipped dry with concentrated electrolyte in separate containers.

The following accessories shall be supplied with each battery set:

Two lead plated lugs for No. 4/0 AWG copper cable.
Two portable hydrometer syringe.
One set of socket wrenches to fit nuts.
Polyethylene bottle with extendable tube for topping up the battery.
Special voltmeters to measure cell voltage.
One gallon of anti-corrosive paint.
The following spare parts shall be supplied with each battery set:
One positive plate
One negative plate
One spare container and cover.
One vent plug
One gallon electrolyte.
The battery shall be tropicalized.
All other features as stated in the table of guaranteed data schedule shall be applicable also.

327
B. BATTERY CHARGER

Charger type : Constant voltage with current limiting

Nominal output voltage : 110 D.C
Input voltage : 433 V (50 Hz) three phases.
Charging operating control : Boost and floating charge, automatic
with manual operation
Maximum charging current : As Required
Provision constant current 15A - 40A : Shall be provided
Provision of constant voltage charge : Shall be provided
90V - 130V

All interconnections, nuts and bolts shall be non-corrosive type.

Battery charger shall come with a voltmeter (0 to 250V DC scale) and suitably scaled
ammeters with 4 inch (approx) dials.
The unit shall have setting knobs for constant charging current within the specified range
and constant voltage within the specified range.
Necessary accessories for battery charger, such as small wiring fuses, terminals, block switches
and other miscellaneous items as well as appropriate tamper proof sheet steel housing for
battery charger shall be provided.
The housing shall have storage space for accessories and provision for locking.
Necessary interconnections between battery and battery charger, DC output terminals, AC
input terminals and AC disconnect switch shall be supplied.

328
 OVERHEAD EARTHING SCREEN
Earthed screens shall be provided at all substations to protect the substation equipment from direct
lightning strikes. The screens shall be of aluminum clad steel wires of not less than 50 sq. mm total
section, and connected to provide low impedance paths to earth.

In accordance with international standards, the ‘Rolling Sphere’ method shall be used to determine
the required protection. The layout of the earth wires shall be such that equipment to be protected
generally lies within areas bounded by two or more conductors.
The earth screens shall be suitable for extension to protect the substation equipment to be installed
in future stages of development.
Connections to the main underground earth grid shall be made of suitably rated copper strap at each
support unless the galvanized steel support structure has sufficient area and current carrying
capacity. Earth wires shall be held in clamps with free pin type joints between clamps and supports.
Connections shall be provided for the terminations of the earth wires of the overhead lines,
including bimetal connectors where necessary.
The design of all structures shall comply with the requirements of the standards and specifications
with consider the layout of the 33/11 kV sub-station. In particular the design shall ensure that in the
event of the breakage of one earth wire, the Factor of Safety is not less than 1.5.

329
 A. ELECTRICAL

3.0 TESTING AND COMMISSIONING

330
 TABLE OF CONTENTS
Clause No. Description Page No

3.0 Testing and Commissioning 306

3.1 Motors 306
3.2 Relays 306
3.3 Instrument Transformers 307
3.4 Electrical Instruments and Meters 307
3.5 AC Switchboards/ Contacts/L.V Equipment 307
3.6 PVC Cable 307
3.7 Metal Clad Switchgear 307
3.8 Disconnectors and Earth Switches 307
3.9 Bushings and Insulators 308
3.10 Current and Voltage Transformers 308
3.11 Structures of Electrical Equipment 308
3.12 Surge Arresters 308
3.13 Batteries and Battery Chargers 308
3.14 Control Panels 309
3.15 Metal Clad Switchgear Busbars 309
3.16 Instruments 309
3.17 Power Transformers 309
3.18 Station service Transformer 311
3.19 Prior to Shipment 312
3.20 Inspection and Testing During Site Erection and Commissioning 312
3.21 Commissioning Tests 313
3.22 Commissioning of Electrical Equipment 315
3.23 Plant Performance 321
3.24 Manufacturer’s Standard Tests 322

331
3.0 Testing and Commissioning
The Contractor shall include comprehensive Inspection and Test Plans in its Quality Plan. Factory
testing shall include all type tests and routine tests set out in the relevant IEC standards and in the
Particular Technical Requirements.

If satisfactory type tests have been carried out on identical equipment the Contractor shall submit
copies of the test certificates to the Employer. The Employer may waive the requirement for any of
the type tests if it approves these test certificates.

The Employer will witness all factory inspections and testing. The Contractor shall notify the
Employer of its intention to conduct factory inspection and testing for each lot of equipment at least
one month in advance, and shall not perform such testing unless the Employer witnesses the test or
a waiver has been provided by the Employer.

The notification shall include full details of the equipment, manufacturers and proposed tests,
including:
Contract identification
Full details of equipment to be tested
Manufacturer's name, address and contact information
Contractor or manufacturer's staff responsible for the testing
Location and date of tests
Schedule of tests to be performed and standard to be applied
List of relevant drawings and documents

In the following sections, various relevant standards and tests are listed. These are not intended to
be exhaustive. If other standards and/or tests are relevant, they shall also apply.

3.1 Motors
One motor of each type and rating shall be type tested and all motors shall be routine tested in
accordance with the tests specified in IEC 60034, NEMA MG 1, IEEE 112, 114, 115 and 85.

3.2 Relays
3.2.1 Type Tests

Type test results shall be submitted for approval for each type and rating of relay.

Type tests may be waived at the Project Manager’s discretion if adequate type tests have already
been performed and copies of the type test reports are supplied.

3.2.2 Routine Tests

All relays and associated equipment shall be routine tested as required by the standards to prove the
quality and accuracy. Routine tests shall be in accordance with relevant IEC recommendations and
BS 142.

All relays shall be subjected to the appropriate routine tests as listed below, the individual tests
being as detailed in IEC 60255 or as otherwise agreed with theProject Manager.

332
 Accuracy of calibrated pick-up and drop-off levels over the effective range of settings
Insulation tests
Accuracy of timing elements
Correct operation of flag (or other) indicators
Mechanical requirements, integrity/safety of draw-out units, check of contact pressure and
alignment.

3.3 Instrument Transformers

All required tests shall be carried out as per relevant IEC standards.

3.4 Electrical Instruments and Meters

One instrument and meter of each type and rating shall be subjected to the test as specified in IEC
60051.

3.5 AC Switchboards/ Contacts/L.V Equipment

Routine tests shall include general inspection and electrical operation tests.

3.6 PVC Cable

Each size and rating of PVC cable shall be subjected to type tests as specified in BS 6346. Routine
tests are detailed in this document.

3.7 Metal Clad Switchgear

One circuit breaker, disconnector, earthing device and other switchgear equipment of each rating
and type shall be subjected to the type tests laid down in IEC 60056, ANSI C37, IEC 62271-100
and other relevant IEC standards. In cases where documentary evidence is produced that a circuit
breaker of exactly similar design has been type tested by an approved and independent testing
station, the type test requirement may be waived.

The circuit breakers of each type shall be either fully assembled at the manufacturer’s works and
subjected to operation tests and power frequency tests or, where not assembled at works, separate
power frequency voltage tests shall be performed on all major insulation components.

Routine tests in accordance with IEC 60056, IEC 62271-100 or ANSI C37 shall be carried out on
all circuit breakers. These shall include operation tests, millivolt drop tests and power frequency
voltage tests. Routine tests in accordance with the relevant IEC standards, including operation tests
and power frequency voltage tests, shall be carried out on all switchgear.

3.8 Disconnectors and Earth Switches

Tests shall be carried out as required according to the following standards:

Type and routine tests to IEC 60129 (BS 5253).

Type and routine tests to IEC 60265 for switch disconnection.
Routine high voltage and mechanical test of insulators.
Sample and type tests of insulators

333
3.9 Bushings and Insulators
Routine, sample and type tests shall be carried out in accordance with the specified standards. Type
tests shall also be carried out unless approved type test evidence is submitted. These tests shall
include temperature cycle and porosity tests.

The following standards shall apply:-

IEC 60233 (BS 4963) for hollow porcelains.

IEC 60137 for bushings.
IEC 60148 and 60273 (BS 3297) for high voltage post insulators.
IEC 60383 and 60305 (BS 137 Part 1 and Part 2) for cap and pin string insulators.

3.10 Current and Voltage Transformers

Type and routine tests shall be carried out according to IEC 60185 (BS 3938), IEC 60186 (BS
3941), IEC 60044-1 and IEC 60044-2.

3.11 Structures of Electrical Equipment

Sample tests on the assembly and galvanizing of the structures shall be carried out. A mechanical
type test with the structure loaded with working load multiplied by the appropriate factor of safety
shall be carried out.

3.12 Surge Arresters

Routine tests and type tests shall be carried out to the specified standards.

The following routine tests shall be carried out on all arrester units in accordance with clause 8.1 of
IEC 60099-4.

Measurement of reference voltage

Residual voltage test
Partial discharge test
Housing leakage test
Current distribution test for multi-column arrester

3.13 Batteries and Battery Chargers

All relevant type and routine tests shall be carried out.
Complete charge and discharge tests on each of the combined batteries and chargers shall be
conducted and results recorded so as to permit verification of the ampere-hour capacity of the
battery. During these tests the Project Manager shall select at random reference cells and the
voltage curves thereof shall be checked when the battery is discharged over three and ten hour
periods. The alarm levels and the automatic voltage control feature of the charger shall be
demonstrated over the specified load range.

334
3.14 Control Panels
Routine operation tests and insulation resistance tests shall be carried out.

3.15 Metal Clad Switchgear Busbars

Routine tests including millivolt drop tests shall be carried out in accordance with the specified
standard. Type tests shall also be carried out on each busbar design unless approved type test
evidence is submitted.

3.16 Instruments
Calibration tests shall be carried out on all important pressure gauges and other instruments as
required by the relevant standards. Site tests shall also be carried out to prove compliance.

3.17 Power Transformers

Testing shall include all routine electrical, mechanical and hydraulic tests in accordance with the
relevant IEC or British Standard, except where departures there from and modifications thereto are
embodied in this specification. For plant not covered by any IEC or British Standard or specifically
mentioned in this specification, such tests as are relevant shall be agreed with the Project Manager.

Should the plant, or any portion thereof, fail under test to give the required performance, further
tests which are considered necessary by the Project Manager shall be carried out by the Contractor
and the whole costs of the repeated tests borne by the Contractor. This also applies to tests carried
out at the Sub- contractors’ works.

After satisfactory completion of the witnessed tests at the works, the Plant shall be submitted for
the Project Manager’s approval during dismantling preparatory to shipment. No item of Plant is to
be despatched to site until the Project Manager has given his approval in writing.

Routine Tests

All transformers shall be subject to the routine tests and routine test sequence (mentioned in
Section VI Part 2 Electrical Transformer Specification (Clause 5)) in accordance with IEC 60076
and the requirements of this Specification.

The test shall be in accordance with IEC 60076, Part 2, and shall be carried out on one transformer
of each size and type. Temperature-rise tests shall be conducted on the tapping corresponding to the
maximum losses.

All relevant type tests shall be carried out or documentary evidence of tests on similar designs
presented.

Temperature Rise Test:

This shall be carried out in accordance with IEC 60076 Part 2.

Noise Level Tests:

A noise level test according to IEC 60075 shall be carried out on one transformer of each type
specified under items 1 and 2 in accordance with IEC 60551.

335
Special Tests

As mentioned in Section VI Part 2 Electrical Transformer Specification (Clause 5).

3.17.1 Voltage Control Equipment

The following tests shall be carried out:

Routine Tests

Each finished tap changer shall be subjected to the routine tests specified in IEC 60214.

Type Tests

Type tests shall be carried out entirely in accordance with IEC 60214 except that evidence of the
service duty type test shall be in excess of 100,000 operations.

3.17.2 Magnetic Circuit

The following tests shall be carried out:

Routine Tests

Each core completely assembled shall be tested for one minute at 2,000V AC between core bolts,
side plates, structural steelwork and core at the core and coil stage. After the transformer is tanked
and completely assembled, a further test shall be applied between the core and the earthed
structural steelwork to prove that the core is earthed through the removable link, at one point only.

3.17.3 Outdoor Bushing Assemblies with Porcelain Insulators

The following tests shall be carried out:

Hollow insulators tested in accordance with IEC 60233.

Complete bushings tested in accordance with IEC 60137.

All relevant type and routine tests shall be carried out.

3.17.4 Tanks

The following tests shall be carried out:

Routine Tests shall include:

Oil Leakage:

All tanks, conservators and oil filled compartments, which are subjected in service or during
maintenance to oil pressure, shall withstand without leakage a hydraulic pressure test equal to 69
kN/m2 or the normal pressure plus 34 N/m2 whichever is the greater, for 24 hours during which
time no leakage or oil ingress into normally oil free spaces shall occur.

336
Type Tests:

Unless type test certificates can be produced for tests carried out on similar equipment, the
following tests shall be included for tanks and conservators.

i) Vacuum Test:

The equipment shall withstand a full vacuum when empty of oil. The permanent deflection of
plates or stiffeners on removal of vacuum shall not exceed the following values:

Length of Plate Permanent deflection

Less than 1300 mm 3.17 mm

1300 to 2500 mm 9.5 mm
Greater than 2500 mm 12.7 mm

3.17.5 Cooling Plant

The following tests shall be carried out:

Routine Tests
Cooler: Pressure test to be as specified above.
Motors and control Gear: as required by the standard

3.17.6 Gas and Oil – Actuated Relays

The following tests shall be carried out:

Routine Tests:

Oil Leakage, when subject to an internal oil pressure of 207kN/m2 for fifteen minutes.
Gas Collection
Oil Surge
Performance test under service conditions
Voltage:2kV for one minute between electrical circuits and casing.

3.17.7 Galvanizing
Routine Tests shall be carried out to the requirements of BS 443 or BS 729 whichever is applicable

3.18 Station Service Transformer

The following tests shall be carried out:

Routine Tests

Measurement of Winding Resistance

Ratio, polarity and phase relationships
Measurement of impedance voltage

337
 Measurement of loss
Short duration power frequency voltage-withstand test
Induced over voltage withstand test
Insulation resistance of each winding

Type Tests

All relevant type tests including a temperature rise test shall be carried out.

Unless acceptable type test certificates cab be submitted in respect of a transformer similar in
design to that specified, a temperature rise test shall be carried out and the costs shall be included in
the contract Price. This test shall take into account temperature rise due to both the specified earth
fault current and continuous operation at CMR of the auxiliary winding.

3.19 Prior to Shipment

After the satisfactory completion of all tests at the factory, the plant shall be submitted for the
Project Manager’s approval during dismantling preparatory to shipping. No item of plant shall be
despatched to site until the Project Manager has given approval in writing.

3.20 Inspection and Testing During Site Erection and Commissioning

3.20.1 General

The Contractor shall be responsible for the inspection and testing during site erection, to ensure
correct erection and compliance with the specification. Tests carried out during testing and
commissioning shall includes those tests listed in this section but shall not be limited to them.

During the course of erection, the Contractor shall provide access as required by the Project
Manager for inspecting the progress of the works and checking its accuracy to any extent that may
be required.

The Contractor shall provide, at its own cost, all labor, materials, stores, and apparatus as may be
required and as may be reasonable demanded to carry out all tests during erection, whether or not
the tests are specifically referred to in this specification. All power supplies (including 50Hz AC)
shall be provided by the Contractor.

A full site test program shall be submitted for approval. This shall include a brief description of all
tests and testing procedures and shall be provided before tests commence and the method of testing,
unless otherwise specified, shall be agreed with the Project Manager.

The Contractor shall provide experienced test personnel and testing shall be carried out during
normal working hours as far as is practicable. Tests which involve existing apparatus and outages
may be carried out outside normal working hours. The Contractor shall give sufficient notice to
allow for the necessary outage arrangements to be made in conformity with the testing program.

The Contractor shall record the results of the tests clearly, on an approved form and with clear
reference to the equipment and items to which they refer, so that the record can be used as the basis
for maintenance test during the working life of the equipment. The required number of site test
result records shall be provided by the Contractor to the Project Manager as soon as possible after
completion of the tests.

338
No tests as agreed under the program of tests shall be waived except upon the instruction or
agreement of the Project Manager in writing.

The Contractor’s test equipment shall be of satisfactory quality and condition and, where necessary,
shall be appropriately calibrated by an approved authority at the Contractor’s expense. Details of
the test equipment and instruments used shall be noted in the test sheets in cases where the
instrument or equipment characteristics can have a bearing on the test results.

The testing requirements detailed under this specification may be subject to some variation upon
the instruction or agreement of the Project Manager where necessitated by change conditions at site
of by differing design, manufacture, or construction techniques.

The Contractor shall be responsible for the safe and efficient setting to work of the whole of the
plant and equipment. The methods adopted shall be in accordance with any safety and permit
regulations in force by the Employer on the site.

3.20.2 Mechanical Equipment

The extent of testing during erection shall include, but not be limited to, the following.

Checking the accuracy and alignment of plant erected. The accuracy shall comply with the
relevant standards, the specification or the plant manufacturer’s requirements as may be
applicable or where no requirements exist, to a standard to be agreed between the Project
Manager and the Contractor.
Checking the alignment of rotating equipment to the manufacturer’s requirements.
Non-destructive testing of site welds as required by the relevant standard and as detailed
in this specification.

3.21 Commissioning Tests

At least two months before commencing the commissioning of any plant or equipment, the
Contractor shall submit for approval fully comprehensive schedules of pre-commissioning checks
as applicable to each item of the plant and equipment provided. These schedules shall then be used
during pre-commissioning as a guide to the methods to be followed and to record the actual
activities carried out with the appropriate date, together with details of all work yet to be
completed, variations and modifications to design conditions.
In addition the Contractor is to submit with the schedules to the Project Manager proforma test
sheets (to be used by the Contractor during testing and commissioning) for all tests he proposes to
carry out and those required by the Project Manager.

Each activity on the schedules, when completed to the satisfaction of the Project Manager, shall be
signed and dated by the Contractor. The schedules shall be countersigned by the Project Manager
as necessary. If during the performance of the pre-commissioning checks the Project Manager
considers that additional tests are necessary to prove the system or plant the Contractor shall
perform such additional tests to the Project Manager’s satisfaction.
Each activity on the commissioning procedure schedules when completed to the satisfaction of the
Project Manager, shall be signed and dated by the Contractor and shall be countersigned by the
Project Manager as necessary.

339
The commissioning procedures shall ensure that the commissioning of any section of the Works
does not interrupt the normal commercial operation of any previously commissioned section(s).
At least 14 days prior to commencing commissioning checks, the Contractor is to agree with the
Project Manager, the method and sequence of performing the commissioning tests. Following
agreement the Contractor shall submit a detailed program indicating the testing sequence to permit
advance notice to be given to the Employer in order that the Employer’s representatives may also
witness testing.

For the purposes of this Contract, the provisions of this section will apply to plant supplied from
nominated sub-contractors.

3.21.1 Contractor’s Site Supervisory Staff

During the commissioning and subsequent testing of any item of plant the Contractor shall provide
the services of any special supervisory staff necessary for the purpose of ensuring proper
commissioning and the satisfactory completion of all tests. The cost of any such specialized
services is deemed to be part of the bid price for erection of plant.

3.21.2 Commissioning of Modified Circuits

Where the scope of works has included the diversion, relocation or variation of any existing circuit
the Contractor is deemed to have included for all pre-commissioning checks on existing equipment.
Where this work includes overhead line or cable circuits the Contractor is responsible for carrying
out full pre-commissioning and on-load checks at the remote end of the circuit including the
injection testing and re-setting of relays if required.
All and any such work associated with the re-commissioning of existing equipment is deemed to be
included in the contract price.

3.21.3 Test Equipment

The Contractor is responsible for providing all equipment, power, etc. necessary to carry out all
tests on site. Following award of contract, at the appropriate time, the successful Contractor shall
submit a detailed schedule of the test equipment etc., he intends to provide for carrying out this
portion of the works. Should the Project Manager require additional or alternative test equipment to
be provided to enable full site testing to be performed in accordance with the requirements of the
specification, the Contractor shall supply such equipment at no extra cost.

3.21.4 Owner Participation

The Contractor shall plan for Employer staff participation either continuously or on a regularly
recurring basis in the commissioning work with the primary intent of:

a) Staff becoming familiar with the operating and maintenance aspects of the new equipment.
b) Staff maintaining a continuing assessment of the precautions required in, or possible
consequences of, initial energization of equipment.

These two objectives must be allowed for in the preparation of schedules.

340
3.22 Commissioning of Electrical Equipment
3.22.1 General
A general check of all the main switchgear and ancillary equipment shall be made and shall include
a cheek of the completeness, correctness and condition of earth connections, labeling, arcing ring
and horn gaps, clearances, painted surfaces, cables, wiring, pipe work, valves, blanking plates and
all other auxiliary and ancillary items. Checks shall be made for oil and gas leaks and that the
insulators are clean and free from external damage. A check shall be made that loose items which
are to be handed over to the employer e.g. blanking plates, tools, spares, are in order and are
correctly stored.

The following general tests are to be carried out on electrical equipment after erection at site:-

Routine high voltage tests to the appropriate IEC standard. Where no relevant standard exists, tests
shall be agreed with the Project Manager.

Insulation resistance tests on all electrical equipment.

Continuity and conductivity resistance tests.
Test operation of alarm and tripping, devices to local and remote.
Rotational tests on all motors.
Polarity tests on CTs and VTs.
Oil tests.
Grounding system and electrode tests.
Ratio, vector grouping and magnetizing current tests on each transformer.
Calibration of winding and oil temperature devices.
Vector group and phasing tests on VT circuits.
Magnetization current/voltage tests, knee voltage, accuracy and winding resistance tests on
all current transformers.
Primary and secondary injection tests on relays, protection devices and equipment.
3.22.2 Transformers
The site tests, full details of which are to be submitted by the Contractor after the Contract has been
placed, shall include those tests described in outline below.

(a) Insulation resistance of core and windings.

(b) Dielectric strength of oil samples.
(c) Ratio and no-load current at low voltage (e.g. 400 V) on all tappings.
(d) Vector notation check.
(e) Calibration check of temperature instruments, including secondary current injection and
proving contact settings.
(f) Air injection tests of gas/oil-actuated relays. (g)
Setting check of oil-level and oil-flow devices.
(h) Complete functional tests of cooling equipment and tap-change equipment, including
manual/automatic sequences, indications, alarms and interlocks, measurement of motor
currents, adoption of suitable motor protection settings and proof of protection for stalled or
single-phasing conditions.
(i) Operational tests of breathers.
(j) Insulation resistance of all secondary circuits.
(k) Carry out “footprint” tests to confirm that no damage to the windings has taken place during
transit and installation.

341
(l) Final checks before energizing:-

Venting, position and locking of valves, earthing of star-point(s) and of tank, state of
breathers and of pressure-relief devices, oil levels, absence of oil leakage, operation of kiosk
heaters, tap-change counter readings, resetting of maximum temperature indicators, final
proving of alarms and trips.

(m) Dissolved Gas Analysis of transformer oil after final processing

(n) Tests when energized:

On-load tap-changer operation throughout range (subject to not exceeding 1.1 pu volts on any
windings).
Maintenance of 1.1 pu volts on untapped windings for 15 minutes (but not exceeding this
value on tapped winding).

(o) Tests on load:

Temperature instrument readings
Measurement of WTI CT secondary currents
Repeat Dissolved Gas Analysis of transformer oil after energisation tests completed

(p) Oil:
Samples of oil from each consignment shall be tested in accordance with IEC 60296 before
dispatch.

Subject to the agreement of the Project Manager a test certificate, confirming that the oil from
which the consignment was drawn has been tested in accordance with IEC 60296, may be accepted.
Before commissioning any transformer, the electric strength of its oil shall be check-tested and
results approved by the Project Manager.

3.22.3 Circuit-Breakers

Circuit-breakers shall be given a visual inspection.

In the case of gas type circuit-breakers testing will be required on the gas system to prove the gas
pressure, quantity, dryness and dielectric strength.

Contact resistance tests shall be carried out. In the case of multi-interrupter circuit-breakers
resistance tests will be required at each interrupter or pair of interrupters as well as through the
series of interrupters on each pole.

Local air components associated with pneumatic operation, including air compressors, shall be
tested and air loss measurements and pressure and alarm settings checked. Tests shall be made also
on mechanical and hydraulic operation systems.

3.22.4 Disconnectors and Earth Switches

Manual operation of disconnectors and earth switches shall be subject to operational tests to
confirm contact pressures, contact resistances, simultaneous operation of all phases and the ease of
operation.

342
Motorised operation of disconnectors and earth switches shall be tested to prove the motor
operation, including local and remote operation, and timing tests shall also be carried out. Motor
protection shall be tested.

Checks shall be made on interlocks, local and remote indications and operation of auxiliary
contacts.

Earth switches shall be tested to confirm the opening and closing sequences and checks shall be
made on interlocks, indications and manual locking devices.

3.22.5 Busbars and Connections

Flexible busbars and connections shall be tested to ensure that the correct tensions, sags and
clearances will be maintained over the range of environmental conditions and loads without stress
to other equipment. If dynamometers are used to check the sags and tensions, they shall be checked
both before and after use.

Rigid busbars and connections shall be tested to ensure that the busbars will not cause overloading
of the supporting insulators under load conditions and under the range of climatic variations
applicable to the site and that expansion and contraction of the equipment is fully accommodated
by flexible connections.

Conductivity tests shall be carried out on all connections and joints which are made on site, without
exception.

3.22.6 Earthing System

Tests shall be made on the effectiveness of the bonding and earthing which will include
conductivity tests on selected joints, on the main earthing system, and at the connections to
equipment and structures. Checks shall also be made on precautions taken to avoid corrosion attack
on the earthing system.

Test probes at approximately 300 and 600 meters separation will normally be required to
effectively test the earthing system. The use of transmission line conductors may be arranged to
simplify test testing procedures.

The earth resistance shall be measured during the installation and on completion as follows:-

of each earth rod after driving

of the earth grid after completion and back-filling of the trenches
of each group of earth rods or earth point after completion of the connection from the
test link terminal.
Of the completed installation without any connections outside the substation

The tests shall be carried out by a method and with equipment approved by theProject Manager. All
tests are to be witnessed and the equipment and method used recorded with the test results.

The Contractor may also be called upon to provide assistance in the measurement of earth
resistance after earth connections to the system have been completed.

343
3.22.7 Control Relays and metering Panels, Instruments and Protective Devices

(a) Wiring

After complete erection and cabling, all circuits shall be subjected to the high voltage test specified
in the relevant IEC or approved standard.

The insulation resistance of all circuits shall be measured before and after any high voltage tests.

For AC secondary injection tests a substantially sinusoidal test supply shall be used.

The operation and resetting level (current and/or voltage) and timing of all relays shall be measured
over an agreed range of settings for all relays.

Other relays shall be fully tested in accordance with the manufacturer’s recommendations.

All DC elements of protection relays shall be tested for operation at 70% rated voltage.

All d/c supplies shall be checked for severity of current inrush when energized by switching on or
inserting fuses or links.

(b) Mechanical Inspection

All panel equipment is to be examined to ensure that it is in proper working condition and correctly
adjusted, correctly labeled and that cases, covers, glass and gaskets are in good order and properly
fitting.

(c) General

Sufficient tests shall be performed on the relays and protection schemes to:

 Establish that the equipment has not suffered damage during

transit.Establish that the correct equipment has been supplied and
installed.
Confirm that the various items of equipment have been correctly interconnected.
Confirm performance of schemes designed on the bases of calculation e.g. differential
protection.
To provide a set of figures for comparison with future maintenance values allowing the
condition of the equipment to be determined.

(d) Secondary Injection

Secondary injection shall be carried out on all AC relays, using voltage and current of sinusoidal
wave form and rated power frequency to confirm satisfactory operation and range adjustment.

The polar characteristic of all distance protections shall be recorded at a minimum of 30 degree
intervals.

For circulating current protection employing high impedance voltage operated relays, the points of
injection for relay voltage setting tests shall be across the relay and stabilizing resistance.

344
The fault setting for the type of protection is to be established by secondary injection, where it is
impracticable to ascertain this value by primary injection. Injection is to be made across the
appropriate relay bus wires with all associated relays, setting resistors, and CT’s connected.

(e) Primary Injection

All current operated relays shall be tested by injection of primary current to record the actual relay
setting and as a final proof of the integrity of all secondary connections.

The stability of all differential schemes shall be checked by injection of primary current.

Primary current injection tests are to be carried out by the Contractor and the methods employed for
a particular installation are to be agreed with the Project Manager.

Tests are to be carried out as follows:

Local primary injection to establish the ratio and polarity of current transformers as a group,
care being taken to prove the identity of current transformers of similar ratio.
Overall primary injection to prove correct interconnection between current transformer
groups and associated relays.
Fault setting tests, where possible, to establish the value of current necessary to produce
operation of the relays.

(f) DC Operations

Tests are to be carried out to prove the correctness of all DC polarities, the operating levels of DC
relays and the correct functioning of DC relay schemes, selection and control switching, indications
and alarms. The correct functioning of all isolation links and fuses shall also be checked.

(g) Tests on Load

Tests on load shall also be done to demonstrate stability and operation of protection relays as
required by theProject Manager.

All tripping, control, alarm and interlocking circuits shall be functionally tested to prove
satisfactory and full proof operation and/or resetting. The functional and safety aspects of all
shorting and/ or isolation links, fuses and switches devices shall be proved.

The total burdens connected to all voltage transformer circuits shall be measured and recorded.

The total capacitance of all wiring and apparatus connected to the negative pole of each main
tripping battery shall be measured and recorded; the value shall not exceed 10 microfarad.

The continuous current drain of all trip circuit supervision relays shall be measured and shall not be
greater than half the minimum current required for tripping. The supervision current shall be
measured with the circuit-breaker (or other device) both open and closed.

Batteries and Chargers

Tests shall be carried out on the batteries and chargers to confirm the charger ratings and
adjustment, the battery and charger alarm systems and battery capacity.

345
The open-circuit cell voltages of the batteries when fully charged shall be recorded.

The insulation to earth of the complete DC installation shall be tested.

Power Cables

Each completed circuit shall be tested for continuity and insulation resistance.

Current Transformers

A magnetization curve shall be obtained for each current transformer in order to:-

Detect damage in transit or installation

Prove that the correct cores have been wired out to the relevant terminals
For high impedance relay schemes, to confirm that correct relay settings have been
calculated.
The DC resistance of each current transformer secondary winding shall be measured and
also the transformers and connection leads, each item being recorded separately.
The insulation resistance of all secondary circuits shall be measured at 1000 volt and
recorded.

Primary current injection tests shall be conducted on all current transformers using adequate
primary current to prove correct ratio, polarity and, for differential protection schemes, to prove the
correct relative polarities of all current transformers of each scheme.

Voltage Transformers

The transformer ratio and polarity shall be checked using a primary voltage high enough to give a
clearly measurable secondary voltage or by using rated primary voltage and comparison with an
already proven voltage transformer. The phasing and phase rotation shall be checked. For three
phase voltage transformers a test shall be conducted to show that energizing each primary winding
produces an output from only the correct phase secondary winding. The residual voltage of any
open delta or broken delta winding shall be measured with rated primary voltage applied.

Control and Instrumentation Equipment

The following general tests shall be performed on control and instrumentation equipment at site:

Insulation resistance testing of all circuits.

Functional tests for all tripping, control, alarm and interlocking circuits.

The testing of all equipment in accordance with the manufacturer’s instructions or as advised by the
Project Manager.

Transformers and Ancillary Equipment

The following tests shall be performed.

Insulation resistance tests on bushings.

Insulation resistance test at 500V between core and core clamping structure.
Voltage withstand tests on insulation oil to BS 148.

346
 Ratio test.
Phase relationship
Magnetization characteristics of current transformers of winding temperature devices.
Calibration of winding temperature devices.
Tap Selector and Diverter Switch alignment.
Calibration of automatic voltage control equipment.
Proving tests as necessary on control schemes.
Measurement of winding resistance on all taps and phases.

3.22.8 Inspection Plan and Procedures

3.22.9 Measuring and Testing Equipments

At prescribed intervals, or prior to each use, all measuring and testing equipment used in inspection
shall be calibrated and adjusted against certified equipment having a known valid relationship to
nationally recognized standards. Where no national standards exist, the basis employed for
calibration shall be approved by the Project Manager.

The manufacturer shall prepare a calibration schedule showing equipment type, identification
number, location, frequency of checks, method of checking and action to take when results are
unsatisfactory.

Each piece of equipment shall be labeled with its identification and current calibration status.

Calibration records for each piece of equipment shall be maintained at least for life of that piece of
equipment and shall be available for examination by the Project Manager.

3.22.10 Re-inspection Following Non-Conformance

If a non-conformance report is issued as specified in this clause and the clause below, the
Contractor shall reimburse the Project Manager for all costs incurred by its staff (including time
costs, travel, accommodation etc.) for both attending discussions on remedial matters and any re-
inspection that the incurred by its staff may deem to be necessary.

3.23 Plant Performance

3.23.1 Guarantees

Bidders shall state and guarantee the technical particulars listed in the Schedules of Technical
Particulars and Guarantees. These guarantees and particulars shall be binding and shall not be
deviated from without the written permission of the Project Manager.
The tolerances permitted in the IEC or other standard shall apply unless otherwise stated.

3.23.2 Rejection
If the guarantees are not met and/or if any items fails to comply with the requirements of this
Specification in any respect whatsoever at any stage of manufacture, test, erection or during the
maintenance period, the Project Manager may reject the item, or defective component thereof,
whichever he considers necessary, and after adjustment or modification as directed by the Project
Manager, the Contractor shall submit the item for further inspection and/or test. The repair
procedure shall be to the Project Manager’s approval. In the event of a defect on any item being of

347
such a nature that the requirements of this Specification cannot be fulfilled by adjustment or
modification, such item shall be replaced by the Contractor, at his own expense to the entire
satisfaction of the Project Manager. Any item of plant repaired to an approved procedure shall not
be accepted as a part of the Works as a permanent solution or replacement unless the Contractor
guarantees in writing that the repaired plant or component shall have the same service life and
efficiency as the component originally manufactured.

3.24 Manufacturer’s Standard Tests

3.24.1 General
Where no specific test is specified then the various items of plant, materials and equipment shall be
tested in accordance with the appropriate IEC standard. Where no appropriate standard is available,
tests shall be carried out in accordance with the maker’s standard practice, subject to the prior
approval of the Project Manager. In all cases, works tests shall include electrical mechanical and
hydraulic tests in addition to any tests called for by the Project Manager to ensure that the plant
being supplied fulfills the requirements of the Specification.
If considered necessary by the Project Manager any multi-part assemblies shall be fully erected in
the Works prior to packing and dispatch to Site.

All tests to be performed during manufacture, fabrication and inspection shall be agreed with the
Project Manager prior to commencement of the work. The inspection schedule included in the
Schedules of Miscellany shall be used for this purpose. The Contractor shall prepare the details of
the schedule and submit these to the Project Manager for approval.
It must be ensured that adequate relevant information on the design, code/standard employed, the
manufacture/fabrication/assembly procedure and the attendant quality control steps proposed are
made available to the Project Manager. The Project Manager will mark in the appropriate spaces
his intention to attend or waive the invited tests, or inspections.

A minimum of 14 days notice in writing, of the readiness of plant for test or inspection shall be
provided to the Project Manager by the Contractor in accordance with the following:
The Contractor shall submit to the Project Manager sequentially numbered applications for
inspection which shall contain the following information.
Contract number
Contract title
Contractors Name
Inspection application number
Manufacturers name, address, telephone and telex numbers, plus name of
manufacturers staff responsible for the testing and manufacturer’s works order number.
Location of tests
Date of tests
Description in full of Plant offered for inspection (Contractors order references alone
are insufficient and unacceptable)
Section of the Works for which Plant is allocated.
Schedule of tests to be performed and standard to be applied.
List of the Employer’s approved drawing numbers appropriate to the Plant offered
Sub-order number

348
The subject items should remain available for the Project Manager inspection and test up to a
minimum of 10 days beyond the agreed date of witnessing the test.

Every facility in respect of access, drawings, instruments, and manpower shall be provided by the
Contractor and his Sub-contractor to enable the Project Manager or his designated representative to
carry out the necessary inspection and testing of the plant.

No equipment shall be packed, prepared for shipment, or dismantled for the purpose of packing for
shipment, unless it has been satisfactorily inspected, and approved for shipment, or alternatively
inspection has been waived. The Contractor shall request permission to dispatch in writing.

Functional electrical, mechanical and hydraulic tests shall be carried out on the completed plant
after assembly in the works. The extent of these tests and method of recording the results shall be
submitted to, and agreed by, the Project Manager in sufficient time to enable the tests to be
satisfactorily witnessed, or if necessary for any changes required to the proposed programme of
tests to be agreed.

All instruments and apparatus used in the performance of the tests shall be to the approval of the
Project Manager, and, if required by the Project Manager, shall be calibrated to an agreed standard
at the National Physical Laboratories or equivalent centre and approved by the Project Manager.

The cost of carrying out such calibrations shall be borne by the Contractor in all cases.

The Project Manager reserves the right to visit the Contractor’s works at any reasonable time
during manufacture of the items of plant and to familiarize him with the progress made and the
quality of the work to date.

3.24.2 Test Certificates

Within 30 days of the completion of any test, four sets of all principal test records, test certificates
and correction and performance curves for the plant and its component parts shall be supplied to the
Project Manager.

These test records, certificates and performance curves shall be supplied for all tests, whether or not
they have been witnessed by the Project Manager or his Representative. The information given on
such test certificates and curves shall be sufficient to identify the material or equipment to which
the certificate refers and should also bear the contract reference title. It shall be possible to identify
the item of plant to which a specific test certificate refers, including those of sub-components and
the specific site for which the item is allocated.

Contractors order numbers or drawing reference numbers are not sufficient for this purpose without
a description of the plant involved.

Test certificate shall provide full details of the measurements of their tolerances, and actual test
values obtained. Certificates simply stating phrases such as ‘Passed’ or ‘Tested in accordance with’
are not acceptable.

When all equipment has been tested, the test certificates from all works and site tests shall be
compiled by the Contractor into volumes and bound in an approved form, complete with index and
included in the appropriate operation and maintenance manuals.

349
 B. CIVIL

4.0 TECHNICAL REQUIREMENTS

FOR SUBSTATION CIVIL AND BUILDING WORKS

350
 TABLE OF CONTENTS
Clause Description
No.
4.1 Introduction
4.2 Design and Construction Standards
4.3 Units of Measurement
4.4 New 33 kV switching Stations
4.5 Site Analysis and Topographical
Survey
4.6 Subsoil Investigations
4.7 Laboratory Testing
4.8 Bulk Earthworks
4.9 Building Foundations
4.10 Civil Work
4.11 Design and Construction Requirements
and Interchangeability
4.11.1 General Requirements
4.11.2 Specific Requirements
4.12 Plant and Equipment Identification
4.12.1 Identification on Drawings
4.12.2 Labels and Nameplates
4.13 Safety and Security
4.13.1 Interlocks
4.13.2 Locks, Padlocks, and Key Cabinets
4.14 Commissioning Spares
4.15 Consumable Items
4.15.1 Chemicals and other Consumable
4.16 Painting and Cleaning
4.17 Galvanized Work
4.18 Steel Pipe Work
4.19 Bolts, Studs, Nuts and Washers
4.20 Architectural and Structural
Requirements of Buildings
4.20.1 Architectural Planning and Design
4.20.2 Structural Design
4.21 Utility Services
4.22 Fire Detection and Protection Facilities
4.23 Grid Substation Sending End Bays for
New Substations
4.24 Preparation of the Site
4.25 Temporary Buildings on Site
4.26 Access to the Site
4.27 Site Drainage
4.28 Site Maintenance during Construction

351
4.1 Introduction

This contract is being tendered as a turnkey contract, in which the selected contractor will be
responsible for carrying out all civil works designs, including preparing working drawings and
specifying materials to be used in all temporary and permanent works. This section describes the
General Technical Requirements for all civil works, which include earthworks, the construction of
foundations, structures, architectural features and all associated works required for REB 33/11 KV
Indoor Rural Type Substations, fitting out structures, buildings and associated works, and erecting,
installing and commissioning of all Substation plant. This section shall be read in conjunction with
the Project Requirements, Schedules and Drawings.

The Contractor shall appoint a team of qualified and experienced engineers and other specialists to
undertake the detailed design of all civil and associated works, and shall submit all completed
designs, drawings and supporting calculations to the Project Manager for approval before site work
commences.

352
4.2 Design and Construction Standards

The design and construction shall conform to the latest edition of the relevant codes of practice and
standards listed below and in individual clauses in this document relating to specific materials or
practice. Any proposed substitution for the listed standards by an equivalent standard shall be
subject to approval by the Employer.
AASHTO American Association of State Highway and Transportation codes for
site access road design
ACI 318-89 Building Code Requirements for Reinforced Concrete
ASTM American Society for Testing and Materials
BNBC (Bangladesh National Building Code) with requirements for building works
BS 12 Portland Cement
BS EN 124 Gully and Manhole Tops for Vehicular and Pedestrian Areas
BS 812 Testing Aggregates
BS 882 Aggregates from Natural Sources for Concrete
BS 1387 Specification for Screwed and Socketed Steel Tubes
BS EN ISO 1461 Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles
BS 1881 Testing Concrete
BS EN 1992-1-1 Design of Concrete Structures (includes foundations)
BS EN 1997-1 Geotechnical Design
BS 2853 Design and Testing of Overhead Runway Beams
BS 3148 Methods of Testing for Water for Making Concrete
BS 3921 Clay bricks
BS 4449 Steel Bars for the Reinforcement of Concrete
BS 5262 External Renderings
BS 5395 Stairs, Ladders and Walkways
BS 5572 Sanitary Pipe Works
BS 5628 Code of Practice for use of Masonry
BS 5930 Code of Practice for Site Investigations
BS 6031 Code of Practice for Earthworks
BS 6367 Code of Practice for Drainage of Roofs and Paved Areas
BS 6399: Part1 Code of Practice for Dead and Imposed Loads
BS 6399: Part 2 Code of Practice for Wind Loads
BS 6465 Sanitary Installations
BS 6651 Code of Practice for Protection of Structures against Lightning
BS 6700 Design, Installation, Testing and Maintenance of Services Supplying
Water for Domestic Use
BS 8004 Code of Practice for Foundations
BS 8005 Sewerage
BS 8100 Lattice Towers and Masts
BS 8102 Code of Practice for Protection of Structures Against Water
BS 8110 Structural Use of Concrete
BS 8206-2 Lighting for Buildings
BS 8215 Code of Practice for Design and Installation of Damp-proof Courses in
Masonry
BS 8290 Suspended Ceilings
BS 8301 Code of Practice for Building Drainage

353
4.3 Units of Measurement

All designs and measurements in this Contract shall be provided in the International System of Units
(SI) in accordance with the provisions of ISO 31 and ISO 1000.

4.4 New 33/kV Switching Stations

Two storied buildings will be designed and constructed to establish a 33 kV Switching stations,
with associated work including control room, complaint room, service road, fencing work,
landscaping and beautification work and other related works.

The Contactor shall be responsible for the design and construction of the Substation and associated
work, which will include the following:
Topographical survey as part of site analysis
Subsoil investigation, sampling and laboratory testing
Master plan including services road, landscaping (beautification work) as per respective
site condition
Conceptual alternative studies of site plans shall be undertaken for individual sites, study
and architectural planning of individual units. The site plan shall consider the building and
other facilities/utilities like circulation roads, parking, utility networks, landscaping and
boundaries.
Foundation works
Architectural plan, section, all side elevation including 3-D perspective of the building.
Structural design as per present code of practices in Bangladesh (BNBC), detail drawings
for construction works.
All required temporary works.
Earth works requirements as per site condition.
Time schedule/work programme, BOQ including rates and all other document,
Maintenance and Operation Manual as required for the process.

354
4.5 Site Analysis and Topographical Survey

The proposed substation sites are located as per drawing locations of Bangladesh. They are
mainly in low lying areas and predominantly paddy land. The Contractor shall carry out a
topographical survey of all substation sites prior to design work commencing, using the most
modern survey equipment available in the country. The Contractor shall first establish a
benchmark on or immediately adjacent to each site on a permanent structure, and establish its level
relative to the nearest PWD benchmark. Detailed digital plans of each site shall be prepared using
AutoCAD at a scale agreed by the Project Manager showing all existing physical features and other
information as listed below and, to the extent necessary, the survey shall extend beyond the site
boundaries to capture adjacent information:

(a) contours at intervals agreed by the Project Manager, extending into the immediate
surroundings of the site;
(b) boundary line of the site;
(c) above ground physical features such as roads, including the nearest National or other main
road, tracks, structures, utilities and plantations;
(d) the location of below ground utilities including piped water supply, gas, drainage,
sewerage and tube wells;
(e) the highest flood level (HFL) at the site and its surrounding areas, related to the
benchmark;
(f) the nearest points at which connections could be made to existing water, electricity and
gas supplies, if available
4.6 Subsoil Investigations

Any previous soil test reports, if available, for each sub-station site will be provided by the
Employer. However, the Contractor shall be fully responsible for all foundation design and must
conduct his own subsoil investigations at every site, the main purpose of which is to determine,
within practical limits, the stratification, ground water table and engineering properties of the soils
underlying the sites of the proposed buildings. The principal properties of interest shall be the
strength, bearing capacity and settlement characteristics of the underlying soils. Efficient, safe,
economical design and construction can be achieved only through adequate evaluation of soil
conditions of the proposed construction.

The Contractor may appoint a sub-contractor (if required) to carry out the site investigations but all
work and all lab work shall be witnessed by one of his own staff who shall countersign all recorded
data.
The record of all boring shall include but not limited to the following information:
(a) Size of the casing (if used)
(b) Number of blows per 300mm required to drive the sampling spoon and data should be
recorded every 1.5 m intervals.
(c) The elevation of the ground surface referred to an established datum
(d) Location and depth of boring and its relation to the proposed construction
(e) Elevation at which samples are taken
(f) Elevation of the boundaries of soil strata
(g) Description of soil strata encountered and any particular unusual or special condition such
as loss of water in the earth and rock strata, boulders, cavities and obstructions, use of

355
 special type of samplers, traps etc.
(h) The level of ground water together with a description of how and when ground water level
was observed

A minimum of five boreholes or augurs shall be drilled at each Substation site and if the results
vary across the site, the Project Manager shall determine whether and how many additional
boreholes shall be drilled.

4.7 Laboratory Testing

The following soil tests shall be performed in a laboratory approved by the Project Manager for
evaluation of soil parameters:
(a) Grain size analysis
(b) Specific gravity
(c) Unit weight (wet & dry)
(d) Natural moisture content
(e) Unconfined compression strength
(f) Direct shear
(g) Consolidation test

The Contractor’s Soil Investigation Reports for each site shall propose full details of foundations
and loading thereon and shall provide estimates of total settlements and differential settlements of
the underlying soil deposits and substantiate the recommendations regarding type of foundation.
The site investigations and analysis of the data in the Reports shall contain but not be limited to the
following:
(a) Location of ground water level
(b) Bearing capacity of the soil
(c) Comparison of alternative types and/or depths of foundation
(d) Data on soil parameters and properties
(e) Settlement predictions
(f) Risks if any to property adjacent to the site.
(g) End bearing value and skin friction for pile design

4.8 Bulk Earthworks

The existing level of all sites are below the HFL, in some cases by up to 5 m, and filling is required
to raise the site level above HFL. The raised ground level of all sites shall be either 600 mm above
the HFL or equal to the level of the nearest main road to the site, whichever is the higher, and also
determined such that water shall not drain from the approach road or main road to the site. It is the
Contractor’s responsibility to determine the fill height required from the topographical survey data
in accordance with the above criteria.

Slope protection works shall also be designed and carried out. This protection should be mainly by
the construction of reinforced concrete retaining walls, pre-cast concrete piles or seasoned wooden
piles, which shall be dependent on the height of filling required as well as existing sub-soil. The

356
Contractor may select and design the type of retaining wall considering the Soil Investigation
Reports and the following:
(a) RCC retaining wall shall be selected where the filling height is above 3.0 m. The
foundation of the wall shall be dependent on the sub soil report.
(b) Pre-cast pile shall be considered where the filling height between 2.0 m to 3.0 m. The
spacing of the pile shall depend on the filling height and size of pile. A rectangular RCC
pre-cast slab of size 1.0 m × 0.5 m shall be used and is to be fixed with the pile by proper
bolting to retain the soil.
(c) Seasoned wooden pile shall be considered where the filling height is below 2.0 m. A
metal sheet with proper treatment shall be fixed with the pile by proper bolting to retain
the soil. The spacing of the pile depends on the filling height and diameter of pile

The fill materials shall be deposited and spread in successive uniform horizontal layers of about
150rnrn thick and compacted by use of mechanical 1.5 ton “Vibro” compactor or other approved
devices to a 98% standard dry density in road and pavement sub-base and 95% standard dry
density for other areas. In filling /back filling against a newly constructed structure precaution must
be taken so that the structure is well matured to take the thrust of filling and when filling against a
wall, the filling shall be carried out from both sides simultaneously.

Tests shall be carried out at a recognized laboratory to ascertain the nature of the fill material and
the degree of compaction obtained for the filled material for which samples shall be taken and
transported to the recognized laboratory by the Contractor at his cost and as directed by theProject
Manager.

4.9 Building Foundations

The type of foundations required will be selected and designed by the Contractor based on the
results of the subsoil investigation and testing program at each new Substation site. The
foundations may be either shallow (spread footings or mat) foundations or deep (pile) foundations
according to subsoil conditions. The Contractor shall submit his foundation design with full
supporting calculation for the approval of the Project Manager. Design shall be according to BS
EN 1992-1-1 and BS EN 1997-1. If deep piles are required, the submission shall include full
details of the type of pile (bored or driven) and the proposed construction sequence.

4.10 Civil Work

Each Substation shall be designed with a two storied control room building (with a foundation
suitable for three stories) with an approximate floor area of 140 sq. m. per story.
Ground Floor (Ceiling Height 3 m): Complaint Centre, Office Room, Rest Room and
Toilet (02 Nos.).
First Floor (Ceiling Height 3 – 3.7 m): 33 kV & 11 kV Switchgear, Control Room,
Battery Room, Toilet (01 No.).
Stair with two flights (run width = 25 cm, riser height = 15 cm and railing with SS/MS
angle).
Great beam height of control room building to be 60 cm above finished ground level.
The outside wall of the control room building shall be covered with Ceramic Bricks and
the floor of the control room shall be Mosaic finishing.

357
 One no. opening with shutter (20 cm wide and full first floor height) at the outer wall of
the first floor of the control room building at a suitable position as per instruction of the
Project Manager (for materials to be carried on the first floor or carried out from the first
floor).
Oil Containment bund walls – for oil drain out one tank to be provided along/beside the
transformer pad.
Cable Trench, Duct and Sump Pits: Cable Trench depth should be provided above flood
level of that area i.e. we should be able to avoid water logging in the cable trench.
RCC Retaining wall along the property line and matching main and personnel gates: RCC
Retaining wall to be constructed along the property line of Substation area including
matching main and personal gates. Structure and foundations for line landing gantries,
plant and equipment. All foundations (including future provisional equipment
foundations), ducts/ drainage, fencing and gates.
33/11 kV Transformer Foundation: Solid power transformer foundation may be
considered in that case rail provision to be provided above x-former pad.
FGL of substation yard should be 60 cm above the highest flood level.
Substation yard surface finishing should be with 25 – 30 mm washed stone gravelling of
7-10 cm depth.
Construction of internal roads (as required).
Substation yard surface finishing should be with 1” – 1.25” washed stone gravelling of 4”
depth.
Supply and installation of Air Conditioning System for Control Room including all other
accessories/ components required for fitting & fixing up to commissioning.
Supply and installation of submersible water pump motor set for safe drinking water
including borehole drilling, pipes and all other accessories/ components required for
fitting & fixing up to commissioning.
All necessary furniture for the Control Room.
Supply and installation of security lights.
Material test results used in construction works.

4.11 Design and Construction Requirements and Interchangeability

4.11.1 General Requirements
The Works shall be designed to operate safely, reliably and efficiently in accordance with the
design and operating requirements stated in this Specification. No violation from the Specification
shall be made subsequent to the Contract without the written approval of the Project Manager.

Each of the several parts of the Plant to be provided shall be of the manufacturer’s standard design,
provided that this design shall be in accordance with an international code of practice and generally
in accordance with this Specification.
The design, dimensions and materials of all parts shall be such that they shall not suffer damage as
a result of stresses under the most severe service conditions. The materials used in the construction
of the Plant shall be of the highest quality and selected particularly to meet the duties required of
them. The plant shall be designed and constructed to minimize correction. Workmanship and
general finish shall be of the highest class throughout.

358
All plant items and corresponding parts performing similar duties shall be interchangeable in order
to minimize the stock of spare parts.

All equipment shall be designed to minimize the risk of fire and damage which may be caused in
the event of fire.

4.11.2 Specific Requirements

The choice of plant and design of the installation is to meet the following criteria:
(a) Sub-station layouts are to utilize the minimum of land area in the existing Substation.
(b) All equipment is to facilitate the installation of all circuits indicated as “future” with the
minimum of disruption. All cabling schemes, D.C. and A.C. equipment etc. shall be
designed to accommodate all such future circuits and loads.
(c) The plant and installation shall be designed for a minimum service life of 25 years.
(d) All plant is to have a minimum of 2 years satisfactory and proven service record of high
durability and reliability in a similar environment. Documentary evidence in support of the
choice of any item of plant shall be provided by the Contractor if requested by the Project
Manager.
Each sub-station is to be designed such that the failure or removal of any one item of plant for
maintenance or repair shall not damage or hamper the operational integrity of the sub-station. The
design and layout of the sub-stations shall ensure the safety of personnel concerned with the operation
and maintenance of the plant.

4.12 Plant and Equipment Identification

4.12.1 Identification on Drawings

The Contractor shall prepare comprehensive plant and equipment Identification Schedules. Each item
in the Schedules shall include the drawing number of the related flow sheet, diagram or drawing
showing that item.

4.12.2 Labels and Nameplates

The Contractor shall supply and install labels, nameplates, ratings, instructions and warning plates,
necessary for the identification and safe operation of plant and equipment at Substations.

Nameplates and labels shall be non-hygroscopic material with engraved lettering of a contrasting
colour or, alternatively in the case of indoor circuit-breakers and starters, of plastic material with
suitably coloured lettering engraved thereon.

All nameplates and labels shall be securely fixed to items of plant and equipment with stainless steel
rivets, plated self-tapping screws or other approved means. The use of adhesives shall not be
permitted.
Individual plant items and all relevant areas within the contract works where a danger to personnel
exists shall be provided with plentiful, prominent and clear warning notices. These warning notices
shall draw attention to the danger or risk with words which attract attention and summarize the type
of risk or danger. The notices shall also carry a large symbol which graphically depicts the type of
risk.

359
All equipment within panels and desks shall be individually identified. The identification shall
correspond to that used in schematic and wiring diagrams.

Each circuit breaker panel, electrical control panel, relay panel etc., shall have circuit designation
label mounted on the front and rear. Corridor type panels shall additionally have circuit designation
labels within the panels.

All equipment and apparatus mounted there on shall be clearly labeled in an approved manner. The
function of each relay, control switch, indicating lamp, MCB, link etc. shall be separately labeled.

The Contractor shall be responsible for the relocation, or replacement of all labels on existing plant,
which becomes inaccurate as a consequence of the contract works.

The language of labels, plates and notices shall comply with the requirements of the Contract.

4.13 Safety and Security

4.13.1 Interlocks

A complete system of interlocks and safety devices shall be provided so that the following
requirements and any other condition necessary for the safe and continuous operation of the plant are
provided:

(a) Safety of personnel engaged on operational and maintenance work on the plant.

(b) Correct sequence of operation of the plant during starting up and shutting down
periods.

(c) Safety of the plant when operating under normal or emergency conditions.

(d) Interlocks shall be preventive, as distinct from corrective in operation.

Where plant supplied under this Contract forms the whole or a part of a system for which one of
more interlocking schemes are required, the Contractor shall be responsible for designing all
interlocking schemes and presenting them for the Project Manager’s approval. General descriptions
of interlocking requirements are given in the Specifications but the Contractor shall include for any
other interlocks he considers necessary.

4.13.2 Locks, Padlocks, and Key Cabinets

The Contractor shall provide padlocks, locks, chains or other locking devices for the locking of all
equipment cubicles, electrical isolating switches, selector switches, valves, etc. to the approval of
the Project Manager.

All locking devices and chains shall be manufactured from corrosion resistant material. All
mechanisms shall be provided with a cover to minimize entry of water or dust.

Locks shall conform to a master keying feature system to be agreed with the Project Manager for
groups of equipment. All locks shall have individual high integrity locks and shall be provided with
three (3) keys. Each key shall be provided with a label as specified.

360
The Contractor shall supply and fit key cabinets equipped with labeled hooks, each Identified with
its appropriate key. Every cabinet shall be provided with a nameplate identifying the cabinet with
its respective item or items of plant. Sufficient cabinets shall be provided to store all keys supplied
under this Contract and cater for future extensions.

The Contractor shall provide comprehensive lock and key schedules to readily permit identification
with equipment and doors. Such schedules are not required for loose padlocks.

Where modifications are performed to existing sites the Contractor shall provide a system identical
to that existing.

4.14 Commissioning Spares

In addition to the spare parts being provided to the Employer, the Contractor is responsible for
ensuring that he has access to a stock of commissioning spares. Spares provided to the Employer
are not to be utilized as commissioning spares without written approval of the Project Manager, in
which case the Contractor shall immediately replace the contract spares at his own expense.

All commissioning spares are considered as Contractors equipment.

4.15 Consumable Items

4.15.1 Chemicals and other Consumable

The Contract includes for the provision of all chemicals, resins, and other consumables required for
testing, commissioning and setting to work of each section of the works.

Unless otherwise stated, the Contractor shall provide all such chemicals and other consumables
required for the efficient operation and maintenance of the plant at full load 24 hours per day for a
period of 12 months for each section of the works from the date of the final certificate.

The Contractor shall prepare a list of these consumables giving quantities necessary for each
section of the works and the recommended suppliers.

4.16 Painting and Cleaning

Immediately following signing of the contract, the Contractor shall submit the names of the
proposed paint supplier and applicator together with a quality assurance program for approval. All
paints for a contract shall be provided by one manufacturer and preferably shall be manufactured in
one country to ensure compatibility.

Painting of the plant shall be carried out in accordance with the appropriate schedule. The work is
generally covered by the schedules but where particular items are not referred to specifically, they
shall be treated in a manner similar to other comparable items as agreed with the Project Manager.

The schedules indicate standards of surface preparation and painting which is intended to give a
minimum service life of 10 years in a coastal industrial environment, with need for minor remedial
work only during that period.
Steel sections and plate shall be free from surface flaws and laminations prior to blast cleaning and
shall not be in worse condition than Pictorial Standard B, Swedish Standard SIS 05 5900.

361
The Project Manager will consider alternative paint schemes to meet the requirements of
fabrication using modern automated materials handling systems, provided they offer the same
standards of surface protection and service life as those intended by the schedules.

All paints shall be applied by brush or spray in accordance with the schedule, except for priming
coats for steel floors, galleries and stairways where dipping is permitted.

Where paint is to be applied by spray, the applicator shall demonstrate that the spray technique
employed does not produce paint films containing vacuoles.

Where paint coatings are proposed for the protection of surfaces of equipment exposed to corrosive
conditions, such as plant items exposed to brines or sea water immersion in liquid, or wet gases, the
coatings shall be formulated to the suitably corrosion resistant and shall be high voltage spark
tested at works and/or at site prior to commissioning. The test procedure shall be based on the use
of a high voltage direct current. The voltage used shall be 75% of the breakdown voltage of the
coating. This breakdown voltage shall first be separately determined using test plates coated with
the specified coating formulation and thickness. The coating on the test plate shall also be micro-
sectioned by the applicator to show that it is free from vacuoles and other defects likely to
invalidate the test procedure.

If the defects revealed by the above test procedure do not exceed one per 5 m2 of coating surface,
the coating need not be re-tested after the defects have been repaired. If the defects exceed one per
5 m2 of coating surface, the repairs shall be resettled after any curing is completed, and this
procedure shall be repeated until the defects are less than one per 5 m 2 of coating surface. After
repair of these defects, the equipment can be placed in service without further testing.

All coating proposed for the internal protection of domestic water storage tanks and shall be
certified by an approved independent Authority as suitable for use in potable water installations and
shall meet the non-painting requirements of BS 3416.

All planished and bright parts shall be coated with grease, oil or other approved rust preventive
before dispatch and during erection and this coating shall be cleaned off and the parts polished
before being handed over.

Where lapped or butted joints form part of an assembly which is assembled or part assembled prior
to final painting, the jointed surfaces shall be cleaned free from all scales, loose rust, dirt and grease
and given one brush applied coat of zinc phosphate primer before assembly.

Paint shall not be applied to surfaces which are superficially or structurally damp and condensation
must be absent before the application of each coat.

Painting shall not be carried out under adverse weather conditions, such as low temperature (below
40° C) or above 90% relative humidity or during rain or fog, or when the surfaces are less than 30°
C above dew point, except to the approval of the Project Manager or his duly appointed
representative.

Priming coats of paint should not be applied until the surfaces have been inspected and preparatory
work has been approved by the Project Manager or his duly appointed representative.

No consecutive coats of paint, except in the case of white, should be of the same shade. Thinners
shall not be used except with the written agreement of the Project Manager.

362
On sheltered or unventilated horizontal surfaces on which dew may linger more protection is
needed and to achieve this additional top coat of paint shall be applied.

The schedules differentiate between ‘Treatment at Maker’s Works’ and ‘Treatment at Site after
Completion of Erection’ but the locations at which different stages of the treatments are carried out
may be modified always providing that each change is specifically agreed to by the Project
Manager and the painting is finished at site to the Project Manager’s satisfaction.

All paint film thickness quoted are minimum and refer to the dry film condition. All thickness shall
be determined by the correct use of approved commercial paint film thickness measuring meters.

The Contractor shall ensure that precautions are taken in packing and crating to avoid damage to
the protective treatment applied before shipment, during transport to the site.

Structural bolts shall be galvanized, sherardized or cadmium plated and painted as for adjacent
steelwork.

All structural timber that does not require to be painted (timber joists, flooring, etc.) shall be treated
with two coats exterior grade approved timber preservative.

The requirements of this clause and the schedules shall be interpreted in accordance with the
requirements and recommendations of BS 5493 and CP 231, 3012 and the paint manufacturer’s
special instructions where applicable.

Colour shall be in accordance with BS 1710 and BS 4800 or equivalent national standards.

4.17 Galvanized Work

All galvanizing shall be carried out by the hot dip process and unless otherwise specified, shall
conform in all respects with IEC’s.

Attention shall be paid to the detail of members, (in accordance with IEC’s). Adequate provision
for filling venting and draining shall be made for assemblies fabricated form hollow sections. Vent
holes shall be suitably plugged after galvanizing.

All surface defects in the steel, including cracks, surface laminations, laps and folds shall be
removed (in accordance with IEC’s). All drilling cutting, welding, forming and final fabrications of
unit members and assemblies shall be completed before the structures are galvanized. The surface
of the steelwork to be galvanized shall be free from welding slag, paint, oil, grease and similar
contaminants.

The coating shall be as specified in BS EN ISO 1461or equivalent National standard. Structural
steel items shall initially grit blasted to BS 4232, second quality (SA2.5). The minimum average
coating weight on steel sections 5 mm thick and over shall be as specified in BS EN ISO 1461.
Bolts, nuts and washers, including general grade high strength friction grip bolts (referred to in BS
3139 and BS 4395 part 1) shall be hot dip galvanized and subsequently centrifuged (according to
BS 729). Nuts shall be tapped up to 0.4 mm oversize after galvanizing and the threads oiled to
permit the nuts to be finger turned on the bolt for the full depth of the nut. No lubricant, applied to
the projecting threads of a galvanized high strength friction grip bolt after the bolt has been inserted
through the steelwork shall be allowed to come into contact with the faying surfaces.

363
During off-loading and erection, nylon slings shall be used. Galvanized work which is to be stored
in works on site shall be stacked so as to provided adequate ventilation to all surfaces to avoid wet
storage staining (with rust).

Small areas of the galvanized coating damaged in any way shall be brought to the attention of the
Project Manager who shall authorize repair by cleaning the area of any weld slug and though wire
brushing to give a clean surface, and application of two coats of zinc rich paint or the application of
low melting point zinc alloy repair rod or power to the damage area, which is heated to 3000C.

After fixing, bolt heads, washes and nuts shall receive two coats zinc rich paint.

4.18 Steel Pipe Work

All steel piping shall be designed, manufactured and tested in accordance with British Standards or
equivalent Nationals Standards approved by the Project Manager. In particular, the minimum wall
thickness of steel pipe work shall comply with Table 2 of BS 1387.

Drains and air vents shall be provided as required by the physical arrangement of the pipe work and
shall be via valves with the drain and vent pipe work led to drain points to the approval of the
Project Manager.

Screwed pipe work systems shall be provided with adequate unions to enable valves and fittings to
be removed if required with minimum disturbance to the rest of the pipe system.

4.19 Bolts, Studs, Nuts and Washers

All bolts and nuts shall conform dimensionally to the requirements of BS 3092 or BS 4190 or
equivalent National Standard.

The Material of all bolts, studs and nuts for piping systems shall conform to the requirements of BS
4505 or equivalent National Standard.

The threaded portion of any bolt or stud shall not protrude more than 1.5 threads above the surface
of its mating nut.

When fitted bolts are used they shall be adequately marked to ensure correct assembly.

Bolts, nuts, studs and washers in contact with sea water or used on pipe work systems containing
sea water shall be of the same material as flanges etc.

The use of slotted screws shall be avoided; hexagon socket screws or recessed type heads shall be
used.

4.20 Architectural and Structural Requirements of Buildings

4.20.1 Architectural Planning and Design

All new buildings and extension to existing buildings shall be designed to be architecturally
pleasing in appearances to the satisfaction of the Employer and to withstand the tropical climate
with minimal maintenance.

364
Architectural plan and elevations of all sides of buildings shall be agreed with the Project Manager
before other details are finalized. All external walls shall be 230 mm first class brick work plus a 50
mm thick layer of Mirpur ceramics facing bricks or similar approved for 10 MVA new sub-station
building as required by the architectural drawing. The internal walls shall be 105 mm thick first
class brick work with plastered and painting of an approved color. For the 5 MVA substations
building internal walls shall plastered with paint finishing.

Bath room floors, walls and stairs shall be tiled. A fixed ladder of galvanized steel shall be
provided up to the roof considering the future provision. Window frames shall be aluminum with
MS grill. Doors shall be wooden and water proofed. A rolling shutter door with a ramp shall be
provided for 10 MVA Substation buildings.

The main entrance to all buildings shall be shaded, either by a projection of the roof over the
entrance verandah or by a separate roof at a lower level. This area of roof shall also be lime
terraced and drained by rainwater pipes.

The service facilities like electricity, water supply and sanitary works, sewerage, gas connection (if
possible) etc. shall be provided as per requirements. Best quality fitting and fixture made in
Bangladesh shall be provided in bathroom in kitchen room. Electrical fittings and fixtures shall be
best quality and wiring provided in Substation buildings shall be internal. Samples shall be shown
to and approved by the Project Manager.

4.20.2 Structural Design

Structural design of Substation buildings shall be according to the Bangladesh National Building
Code (BNBC). Loads for reinforce concrete design shall be calculated as the sum of dead loads,
live loads and environmental loads (wind and seismic) as explained in the BNBC. Ultimate
Strength Design (USD) method (BNBC Chapter 6) shall be adopted for design of all reinforce
concrete structural elements.

The roof shall be a cast in situ concrete slab designed for 2.5 kN/m 2 live load. The ground floor
slab shall be cast as per cable trench layout which shall be considered as slab on grade (RBC floor).

4.21 Utility Services

Utilities shall be designed and installed comprising:

(a) Plumbing system including wastewater and surface water drainage system development
including septic tank, soak well, and surface or buried drain.
(b) Water supply and sanitary work.
(c) Electrical works includes internal wiring, fitting, fixing all necessary items, internal
lighting, street lighting, necessary earthing.
(d) Telephone if needed.

4.22 Fire Detection and Protection Facilities

The Contractor shall design, manufacture, deliver to the Site, install, test and commission the
firefighting system to protect each Substation, all plant associated equipment and outdoor yard. In
particular, the following shall be included:

365
 (a) Fire Detection and Alarm system: fire detection shall be by means of smoke detectors and
ultra violet flame detectors with a backup system utilizing rate-of-rise temperature
detectors, along with an alarm system.
(b) Balancing, testing and commissioning of fire detection and alarm system for 16 zone.
(c) Dry chemical powder and carbon dioxide type fire extinguishers.
(d) Five wall mounted sand buckets outside the control room building at suitable place
locations

A reinforced concrete fire wall is required between two transformers in future provision for 10
MVA substations. The wall size shall depend on the transformer size. The Contractor shall prepare
proposed designs for approval of the Project Manager.

4.23 Grid Substation Sending End Bays for New Substations

Some of the new Substations shall have direct connections from grid substations. Bays and busbar
must be available for facilitating this connection. Where existing bay and busbar space is not
available, new bays shall have to be designed and constructed and the existing busbar extended.

The Contractor shall be responsible for designing and constructing the grid substation foundation
for 33KV circuit breaker, CT, gantry extension to construct new feeder bays and bays extension
including earth grid where required including installing bay equipment and associated works. The
design and drawings shall be submitted for the Project Manager’s approval before any work
commences at site.

4.24 Preparation of the Site

Boundary pillars of standard designs shall be fixed on the ground to define the boundary of the site.

Refuse or superfluous earthon the site shall be removed before construction begins. Shrubs and
stumps of treesshall be uprooted and removed off site. Any valuable material derived from the
clearing of the site should be stored and disposed of according to the BNBC.

No tree shall be cut down or pruned unless prior approval is given by the Project Manager. A
survey report must be submitted and sanctions obtained before the trees are disposed of. If white
ants are found to exist in the trees, their nests shall be located and dug up and the queen ant be
destroyed. Holes left after uprooting of the trees shall be backfilled with sand or earth, care being
taken that the fill, on compaction, achieves the density of the surrounding soil.

The Contractor’s Engineer himself shall set out all important levels for permanent works using the
site benchmark established during the topographical survey. Areas for storage and stacking of
materials should be set out and pegged, similarly the position of temporary buildings, the access
road and site roads.

The Contractor shall not fell any tree outside the site boundary without the express written
permission of the land possessor, even if such tree is an obstacle to execution of the work.

4.25 Temporary Buildings on Site

Locations of temporary offices, guard sheds, work sheds and accommodation on each site shall be
selected such that they do not clash with the location of permanent work and do not interfere with

366
construction work. Prefabricated buildings that are simple to erect and dismantle, yet provide a
pleasing look, are preferred.

4.26 Access to the Site

The access road to each site shall generally be of the shortest possible length from the nearest main
road. While designing the road alignment, the Contractor shall maximize natural slopes as much
as possible for drainage of rainwater and the facilities shall be secured effectively and
economically. The design and drawings shall be prepared by the Contractor to current practices
AASHTO codes of practice.

4.27 Site Drainage

The entire surface of each Substation site within its boundary walls shall slope at 1 in 150
minimum gradient to open channels around the entire perimeter. These channels shall be designed
for a rainfall intensity of 60 mm per hour. Outside the boundary wall, the Contractor shall be
responsible for drainage up to 20 meters, or to suit each sites requirements, from the wall and the
drainage outlets at some sites may be need to be provided with suitable erosion protection down to
paddy level.

The ground immediately adjacent to foundations shall be sloped away from them at a slope of not
less than 1:12 for a minimum distance of 205 m measured perpendicular to the toe of the wall.
Consideration shall be given to possible additional settlement of backfill when establishing the final
ground level adjacent to foundation.

A 75 mm layer of crushed rock (average size 30 mm) shall be placed across the entire site,
extending 1 m outside the fence.

The concrete wall of cable trenches shall project at least 70 mm above brick paving level to prevent
run off entering the cable trench. The floors of all cable trenches or tunnels shall be sloped to
soak aways.

The cable trenches shall be free from surface water drainage. If the cutoff area exceeds 30 m 2 it
shall be drained by a concrete pipe sized to take the runoff to the boundary drain. The Contractor’s
drainage design shall avoid all ponded water to avoid forming a mosquito breeding ground.

All drainage pipe work except cable trenches within buildings shall be UPVC pipe of diameter as
per design requirement. But cable trenches are RCC work as per design requirements.

The floor slab shall be constructed in reinforced brick concrete (RBC) floor125 mm thick and
foundations for controlling equipment in RCC.
External pipe work shall be 150 mm minimum diameter concrete pipes at a minimum depth of
invert of 600 mm. Where pipes, including existing pipes along with site, are less than 400 mm
above adjacent foundations, they shall be surrounded in concrete. Where required, drainage pipes
shall be kept below cables, allowing 1.1 m cover to the top of pipes.
Manholes shall be of brick construction with 500mm x 500mm clear openings and air tight ductile
iron covers to BS EN 124. Manholes shall be located at all changes of pipeline direction. The
minimum gradient for all pipelines shall be 1 in 80. Manholes shall not be located in roads.
The Contractor shall be responsible for all negotiations with local authority (WASA) where a
connection to a public sewer is proposed. The Contractor shall provide all protection required to

367
existing sewers and shall deepen foundations, including boundary wall foundations, where required
all foundations are below adjacent sewers.

Each control building shall be provided with a septic tank designed for 10 users and a soakaway of
open brick construction 11 m deep by 2.2 m diameter filled with broken bricks. The septic tank
shall be located at suitable place of the area. The inner surface of all manholes and septic tanks
shall be painted with two coats of bitumastic paint to protect it against sulphate attack. The septic
tank shall have access holes directly over the inlet pipes and outlet pipes. Where public sewers exist
along the side of substation site, the Contractor shall connect directly to the sewerage line from the
soakaway. Two vents of minimum height 2.2 m shall be provided on each septic tank.

4.28 Site Maintenance during Construction

a) The site shall be kept as clean as reasonably possible during construction. Materials
shall not be stacked haphazardly but kept in a planned manner in proper stacks. Care
shall be taken to maintain the site with proper drainage of rain and stagnant water.
b) The proposed roads should be laid out and used for carriage of materials to avoid
vehicles travelling randomly over the site and spoiling it. The base of the road may
also be laid and maintained during construction.
c) Any rejected materials, dismantled materials and other items not required in the
construction shall be removed from the site immediately, so that there is no chance of it being
used by the Contractor’s labour.

368
 B. CIVIL

5.0 SUBSTATION BUILDINGS AND ANCILLARY FACILITIES

369
 TABLE OF CONTENTS

Clause No. Description

5.1 Civil Works-General
5.2 Mobilization and Preparation of the Site
5.3 352Dismantling & Removal of Existing Structures for Rehabilitation Sites
5.4 353 Site Office Facilities for the Engineer
5.5 354 Earth Work in Excavation For Structure
5.6 354 Brick Flat Soling (BFS)
5.7 355 Lean Cement Concrete (CC) Works
5.8 355 Cement Concrete In Floor
5.9 356 Damp Proof Course
5.10 356 Reinforced Cement Concrete Work (RCC)
5.11 356 RCC with Water Proofing Admixture
5.12 365 Reinforcing Steel In Concrete
5.13 365 Brick Work
5.14 368 Patent Stone Flooring
5.15 369 Ceramic Tiles
5.16 370 Plaster Work
5.17 371 Neat-Cement (Skirting/Dado)
5.18 372 Making Groove On Wall Surface
5.19 373 Painting Works
5.20 374 Timber Works
5.21 376 Metal Works
5.22 378 Aluminum Doors, Windows etc.
5.23 379 Water Proofing Polythene Sheet
5.24 382 Lime Terracing on Roof
5.25 382 Screeding on Roof
5.26 383 Surface Drain
5.27 383 Apron
5.28 383 Road Work
5.29 384 Clearing after Completion
5.30 387 As Built Drawings
5.31 Tests for Materials

370
5.1 Civil Works-General
This specification has been prepared with all possible care and diligence and every effort has been
made to cover all types of materials and items of works necessary to complete the Project in all
respect.

All workmanship and materials to be used in the Works shall be of the best quality of their
respective kinds as specified herein. All materials used in the Works shall be new and obtained
from the sources and suppliers approved by the Project Manager. Materials shall comply strictly
with the requirements prescribed hereinafter or, where such requirements are not specified in this
specification, the latest issues of the relevant Technical Standard shall be followed. All tests of
materials shall be done by laboratory approved by the Project Manager. The accuracy and
sufficiency of information furnished in this specification is not guaranteed. It is the responsibility of
the Contractor to clear any confusion or ambiguity in this specification well ahead of submission of
bid. In case of any missing item relevant standard specification shall be followed.

5.1.1 Materials
5.1.1.1 Cement

Cement shall be Ordinary Portland Cement conforming to the requirements of the Standard
Specifications for Portland Cement Type -I, ASTM C-150 or BDS 232 (2nd Revision) unless
otherwise specified.

Cement shall conform to the following standards as per BDS 232 (2nd Revision) and ASTM C109,
C191, C204.
a) Water for normal consistency : 26% to 33%
b) Fineness : Minimum 280 sq. m./kg (by air
permeability method)

i) Initial setting time, ASTM C191 : Not less than 45 min. :

ii) Final setting time, ASTM C191 Not less than 375 min.

c) Minimum compressive strength

i) 3rd. day : 9.45 Mpa (1350
ii) 7th day psi) : 14.7 Mpa (2100
iii) 28th day psi) : 21.0 Mpa (3000
psi)

Cement shall be delivered in packages as packed by the Manufacturer with the brand name, type of
cement and weight of each bag marked on the bag. Sample test of cement must be done by
laboratory approved by the Project Manager: Two bags from each brand or each consignment of
supply of 25 metric tons of cement shall be selected for testing. The Project Manager require the
Contractor to have the cement tested or can take samples in the presence of Contractor from cement
bags stored at work site and send them to an approved laboratory for testing.

Cement of doubtful quality shall not be used until satisfactory results are obtained. All cement not
conforming to specifications and cement that has deteriorated, been damaged or has set shall not be
used and shall be immediately removed from work site by the Contractor. The cost of all such
cement shall be borne by the Contractor.

371
5.1.1.2 Brick

Common building clay bricks shall conform to BDS 208 (First Revision).

Bricks shall be manufactured from combination of clay mixed with silica sand and alumina and
shall be uniformly burnt throughout. Bricks shall be kiln burnt.

First Class Bricks

First Class Bricks shall comply with the following requirements of BDS 208 (Common Building
Clay Bricks –First Revision)

a) Bricks shall be of machine mould, uniform colour, shape and size having sharp square sides
and edges and paralleled faces.
b) Bricks shall be sound, hard and well burnt homogeneous in texture and free from flaws and
cracks.
c) Bricks shall emit a clear metallic sound when struck with a small hammer or another brick.
A fractured surface shall show a uniform compact structure free from lumps, grits or holes.
d) A first class brick shall not absorb more than 1/5th of its dry weight when immersed in water
for 24hours.
e) A first class brick shall not break when struck against another brick or when dropped at T-
position on hard ground from a height of about 1.2 meter.
f) Standard dimension of bricks shall be 240 x 115 x 70mm (9.5” x 4.5” x 2 .75”)
g) Allowable variations in dimensions shall be:
i) in length not more than 6 mm ii)
in breadth not more than 5 mm iii)
in height not more than 1.5 mm
h). Unit weight of bricks shall be minimum 1100 kg/cum
i) Minimum compressive strength of bricks shall be for i)
Halved bricks (mean of 12 bricks): 28 Mpa (4000 psi)
ii) Individual brick: 21.1 Mpa (3000 psi)
j). Range of efflorescence for a first class brick shall be slight to nil.
Picked Jhama Bricks
Picked Jhama-Bricks shall be over-burnt First Class Bricks, uniformly vitrified throughout with
good shape, hard slightly black in colour, and without cracks or spongy areas. Minimum
compressive strength shall not be less than 28 N/mm2 (4000 psi)

All other requirements for First Class Bricks shall apply to Picked Jhama except for dimensions.
Perforated Bricks

Perforated bricks shall meet the following specifications:

a) Minimum unit weight : 3.00 kg/brick
b) Minimum compressive strength on gross
area:
i) Multi-core brick : 70kg/sq.cm
ii) 10-Hole engineering brick : 210kg/sq.cm
iii) Maximum size of perforation : 25sq.mm
c) Minimum number of perforation
i) Along width of brick : 2

372
 ii) Along length of brick : 6
d) Minimum wall thickness:
i) Between brick edge and perforation : 10mm

ii) Between adjacent perforations : 10mm

e) Maximum water absorption
i) 5hrs, boiling : 20% of dry wt.

ii) Efflorescence : Nil

” ”
Dimensions (3mm) 24cm × 11cm × 7cm (9.5 × 4.5 × 2.75”)

The perforations may be of any regular shape in cross section, In case of rectangular section the
larger dimension shall be parallel to length of the brick. Dimension of perforation measured parallel
to the plane of the shorter side shall not be more than 15cm except in case of circular shape of the
perforation in which case it may be allowed up to 20 cm. Total area of perforation shall not exceed
45% of the total area of corresponding face of the brick.

Clinker Bricks

Clinker bricks or tiles shall meet the following requirement:

Minimum unit weight : 2 kg/brick

Minimum compressive strength : 560 kg/sq.cm
Minimum modulus of rupture (8000psi) : 560
Water absorption 5 hrs. boiling kg/sq.cm (600psi) : 12%-
15% of dry wt.
Efflorescence
: Nil
Dimensions
: 200 mm x 100 mm x 5 mm
(8” × 4” × 2”)
Clinker bricks shall be manufactured by dry process and burnt to a higher temperature and shall
uniformly vitrified to a dark copper tone. Edges shall be square, straight and sharply defined.

5.1.1.3 Sand (Fine Aggregate)

Sand shall conform to BDS 243, ASTM C 33

Sand shall be either natural sand, composed of clean, hard, durable uncoated particles resulting
from the disintegration of siliceous and/or calcareous rocks; or manufactured sand resulting from
the crushing of boulders or shingle.

The maximum size of the particles shall be 4.75 mm (3/l6 in) and shall be graded down.

Sand shall be clean and free of injurious amounts of organic impurities; deleterious substances shall
not exceed the following percentages by weight:

Clay Lumps and friable particles-Maximum 3%

Coal and Lignite 0.25%
Material passing the 0.075mm (No. 200) sieve 1%
Shale, coal, soft or flacky fragments 1%
Sulfur compounds 0.3%
no organic material.
Organic material content

373
Sand shall be well graded from coarse to fine and shall conform to the following Fineness
Modulus:

Concrete : 2.5 (Two point five)

Concrete : 1.5 (One point five)

Mortar : 1.5 (One point five)

Filling sand : 1.0 (One point zero)

: 0.8 (Zero point eight)

Sand from different sources of supply shall not be mixed and stored in the same stock pile nor used
alternately in the work without permission from the Project Manager.

5.1.1.4 Coarse Aggregate

Coarse aggregate shall conform to BDS 243 (Coarse and Fine Aggregates from Natural Sources for
Concrete 1; ASTM C 33: Concrete Aggregates).
Nominal maximum size of coarse aggregate in concrete shall not be larger than:

a) One-fifth of the narrowest dimensions between sides of forms; or

b) One-third the depth of slabs; or
c) Three-fourth the minimum clear spacing between individual reinforcing bars or wires,
bundles of bars.

The Boulder

The boulders to be used for coarse aggregate in concrete shall be composed of limestone,
sandstone, granite, trap rock or rock of similar nature and shall have the following properties.

Compressive strength (minimum) 35Mpa (5000psi)

Specified gravity 2.2-2.6
Unit weights 22-25.1 kn./cum
Porosity 2.10%
Water absorption (maximum) 2.5% by wt

The boulder shall be of uniform light color as approved and shall be free of thin laminations,
adherent coatings, and deleterious substances. The wear loss of coarse aggregate of all types shall
not exceed 35% by weight when tested by the Los Angeles Abrasion Test.

5.1.1.5 Water

The water used in mixing and curing concrete shall be tested for chlorides and sulphates in a
standard material-testing laboratory as directed by Project Manager. The maximum acceptable
limits shall be as follows:
1000mg/I as S03 for sulphates
500mg/l as Cl ion for chloride

374
Water shall be clear and free from salt, oil or acid, vegetable or other substances injurious to the
finished product. The pH values of water shall generally be not less than 6. Water used in
construction work shall be potable.

5.1.1.6 Admixtures

Admixtures used for the purpose of modifying the normal plastic life of concrete mix or for
influencing its rate of gaining hardness and strength or for the workability or concrete shall not be
used except with the written approval of the Project Manager.

Admixture if specified or permitted shall conform to the requirements of AASHTO Standard

Specification M-194/ASTM, C-494 or ASTM C-1017.

It shall be kept in mind that a small change in the amount of admixture may cause great change in
their action and their adequacy of performance is difficult to measure at the construction site during
the progress of work. Water reducing admixture, accelerating admixture, water reducing and
retarding admixtures, water-reducing and accelerating admixtures shall conform to ASTM C-494
(Chemical Admixtures for Concrete) or ASTM C-1017 (Chemical Admixtures for use in producing
flowing Concrete)

5.1.1.7 Reinforcing Bar

High tensile steel reinforcing bar shall be structural grade deformed bar specified as per ASTM,
A615M, and BOS 1313: 91, Bars having minimum yield levels of 275 Mpa (40,000 psi) and 415
Mpa (60,000 psi) are designated as Grade 40 and Grade 60 respectively. High tensile steel
reinforcing bars shall meet the following strength test requirements:

Properties Grade 40 Grade 60

Yield strength 275 Mpa 415 Mpa
(minimum) (40000 psi) (60000 psi)
Ultimate strength 483 Mpa 620 Mpa
(minimum) (70000 psi) (90000 psi)

Tolerance on Mass

Nominal size Tolerance of mass per

(mm ) Meter run (%)
Up to 7 8.0
8 to 12 6.0
Over 12 4.5

Tolerance on Diameter

Tolerance in diameter for both plain and deformed bars shall not exceed 2.5% for 12mm and less
size and 1.8% for sizes larger than 12 mm.

375
Tensile Requirements

Grade 40 Grade 60
Tensile strength, min. psi 70000 90000
Yield strength min. psi 40000 60000
Elongation in 8 in min. %
Bar Nos.
3 (10mm) 11 9
4 ,5, 6 (12, 16, 20 12 9
mm)
7, 8 (22, 25 mm) … 8
9, 10 (28, 32 mm) … 7
11, 14, 18 … 7
(35, 45, 57 mm)

Bending Requirements

The bend-test specimen shall withstand being bent around a pin without cracking on the outside of
the bent portion. The requirements for degree of bending and sizes of pins are prescribed in Table 3
-Bend Test Requirement.

The bend test shall be made on specimens of sufficient length to ensure free bending and with
apparatus which provides.

Continuous and uniform application of force throughout the duration of the bending
operation.

Unrestricted movement of the specimen at points of contact with the apparatus and bending
around a pin free to rotate.

Close wrapping of the specimen around the pin during the bending operation.

Bend Test Requirements

Bar Designation No. Pin diameter for Bend TestA

Grade 60 Grade 40
1 b
3,4,5 3 /2 d 31/2d
6 5d 5d
7,8 5d --
9,10 7d --
11 7d --
0
14,18 (90 ) 9d --
A 0
Test bends 180 unless noted otherwise.
db = nominal diameter of specimen

376
Frequency of Tensile, Bend, Rebend testing

Nominal size of Value of x (Quality of materials in tones)

bar (mm) Tensile test Bend test Rebend test
Under 10 25 50 50
10 to 16 35 70 70
20 to 32 45 90 90

For the specified tests sample length shall be 600 mm long or 20 times the nominal size whichever
is greater. Sample shall be selected from each batch at a frequency of not less than one up 5 (five)
tones or part thereof where x has the value given in the above table. Samples from the bend and
rebend tests shall not be selected from the same bar.

Cross Sectional Area and Mass

Nominal size Mass (kg/m) Cross sectional are (mm2)

6 mm 0.222 28.30
8 mm 0.395 50.30
10 mm 0.616 78.50
12 mm 0.888 113.00
16 mm 1.579 201.00
20 mm 2.466 314.00
22 mm 2.980 380.00
25 mm 3.854 491.00
28 mm 4.830 616.00
32 mm 6.313 804.00

All steel bars prior to its use shall be cleaned with wire brush to make it free from loose scale, dirt,
paint, oil, grease or other foreign substances.

All reinforcing steel shall be stored properly under shed not to be contaminated by oil, grease or
mud.

Requirement for Deformation in Reinforcing Steel

The requirement of deformation shall meet ASTM A615.

a) Deformations shall be spaced along the bar at substantially uniform distances. The
deformations on opposite sides of the bar shall be similar in size and shape.

b) The deformations shall be placed with respect to the axis of the bar so that the included
angle is not less than 450 deg. Where the line of deformations forms an included angle with
the axis of the bar of from 450 to 700 deg inclusive. The deformations shall alternately
reverse in direction on each side, or those on one side shall be reversed in direction from
those on the opposite side. Where the line of deformation is over 70 0 deg. a reversal in
direction is not required.
c) The average spacing or distance between deformations on each side of the bar shall not
exceed seventeenths of the nominal diameter of the bar.
d) The overall length of deformations shall be such that the gap between the ends of the
deformations on opposite sides of the bar shall not exceed 12.5% of the nominal perimeter

377
 of the bar. Where the ends terminate in a longitudinal rib, the width of the longitudinal rib
shall be considered the gap. Where more than two longitudinal ribs are involved, the total
width of all longitudinal ribs shall not exceed 25% of the nominal perimeter of the bar.
Furthermore, the summation of gaps shall not exceed 25% of the nominal perimeter of the
bar. The nominal perimeter of the bar shall be 3.14 times the nominal diameter

e) The spacing/height and gap of deformations shall conform to the requirements prescribed in
Table 1 of ASTM A615.

f) Any bar that fails to satisfy the above requirements is to be treated as plain reinforcement
according to ACI Building Code Requirements for Reinforced Concrete ACI 318-95.

5.1.1.8 Timber for Doors/Windows

Timber for doors shall conform to BDS 142; specification for Wood Doors (under revision): BDS
820, Recommendation for maximum permissible moisture content of timber used for different
purpose in Bangladesh.

Timber used for doorframe and leaf shall be well-seasoned, dry and straight grained, free from
knots and other defects affecting its appearance, strength and durability. All timbers used for
doors/windows shall be mechanically seasoned and the moisture content shall not be more than 12-
13%.

5.1.1.9 Aluminum Sections

All Aluminum Sections shall conform to U.S. Architectural Aluminum Manufactures Association
Standards (AAMA).

The following are the standards to be followed for Aluminum doors, windows and curtain walls or
as specified in Bill of Quantity:

Channel thickness for doors : 1.8 -

Channel thickness for windows 2.5mm :
Anodization thickness 1.2 -
Density of anodization 1.8mm :
5.1.1.10 Glass 15 microns
: 4mg per sq.m.

Glass for aluminum door and window tinted or clear should be 5mm thick and there should
be no undulations
For smaller wooden panel/M.s. glazed shutters glass should be 3mm thick and there should
be no undulations.

5.1.1.11 M.S. Pipe

M.S. pipe shall be made from low carbon steel conforming to ASTM A53 and following
physical requirements:

378
 Nominal Wall Inside Outside
Weight
Pipe Thickness Diameter Diameter
(kg/m)
Diameter (mm) (mm) (mm)
150 mm 7.11 154.08 168.30 28.26
100 mm 6.02 102.36 114.40 16.07
75mm 5.49 77.92 88.90 11.29
50mm 3.91 52.48 60.30 5.44
25mm 3.38 26.64 33.40 2.50
20mm 2.87 20.96 26.70 1.69
12mm 2.77 15.76 21.30 1.27

5.1.1.12 UPVC Pipe

UPVC pipe shall be of Unplasticised Polyvinyl Chloride (UPVC) and shall conform to the
following specifications:

Specific Gravity : 1.36 -1 .43

2 2
Tensile strength : 450 Kgf/Cm -560 Kgf/Cm :
Elongation 80%
Compressive Strength 2
: 600-700 Kgf/Cm

Mean outside Schedule 40 Wall Schedule 80 Wall

Nominal Size
Diameter (MM) Thickness (mm) Thickness (mm)
Inch (mm) Min Mix Min Mix Min Mix
2.00” 50 60.17 60.47 3.91 4.42 5.54 6.20
3.00” 75 88.70 89.10 5.49 6.15 7.62 8.53
4.00” 100 114.07 114.53 6.02 6.73 8.56 9.58
5.00” 125 141.05 141.55 6.55 7.34 9.52 10.66
6.00” 150 168.00 168.56 7.11 7.79 10.97 12.29
8.00” 200 218.70 219.46 8.18 9.17 12.70 14.22

5.2 Mobilization and Preparation of the Site

Description

This item shall consists of mobilization of man powers, materials & equipment and preparation of
site by clearing off of the site of rubbish of all kinds including surplus earth, slurry, weeds, grass
etc., cutting and uprooting of trees of all girth; removal of drains, dewatering & bailing out of
water, during whole construction period, sewers or any other services, leveling of site including
filling, if necessary, protection of the periphery of the site by earth to prevent passage of any
outside rain and waste water etc. dismantling of existing structure if any, and removal of surplus
materials and debris to a safe distance as directed by the Project Manager.

379
Construction Requirement:

Before setting out the new work and commencing foundation work the site must be cleared off of
all those described above. On clearance of site it should be roughly leveled as required.

The trees shall be cut and their roots totally up-rooted as directed by the Project Manager No tree
should be cut unless it is absolutely unavoidable. All serviceable materials obtained from the
clearing shall be property of the competent authority as determined by the Project Manager.
Salvaged material may be handed over by the Contractor to the local authority on instruction from
the Employer.

5.3 Dismantling & Removal of Existing Structures for Rehabilitation Sites

Description
This item shall consists of the removal/ dismantling and satisfactory cleaning, stacking, storing or
disposal, inside or outside the site of such portions of existing structures as provided in the Plans,
Schedule of Quantities and Specifications or ordered by the Project Manager. This includes all
items such as breaking and removal of khoa debris, concrete, R.C.C, brick work, plaster and other
items as mentioned in schedule of quantity or as directed by the Project Manager.

Construction Requirement

Before commencement of removal/ dismantling work, the structure or parts thereof shall be
properly earmarked and necessary arrangement for stabilization of the adjoining structures shall be
ensured by means of adequate shoring, shuttering, propping and strutting. The dismantling work
shall not commence until the arrangement of safety of the adjoining structure has been insured by
the Contractor, inspected and approved by the Project Manager. The Contractor shall be solely
responsible for any damage to the portion of structure which' were not intended to be dismantled
and make good the damages, if any, at his own cost. The Contractor shall comply with all safety
regulations and shall furnish, erect and maintain suitable barricades and warning signs and take
such other measures as necessary to prevent personal injury or property damage. All these
barricades, warning signs shall comply with the by-laws, regulations and provisions of BNBC and
shall be to the satisfaction of Employer, and Local Authorities concerned.

This item of work also includes cleaning and sorting out of the salvaged materials in a usable
condition, transporting and storing neatly for use/disposal as directed by the Project Manager. The
items of dismantling works of different structures in foundation also include all excavation, bailing
out water by pumping, drainage, bracing, shoring, etc. as found necessary and their subsequent
removal and satisfactory disposal of all materials obtained from such excavations and backfilling to
the level of original ground where required. The Contractor shall keep adequate records of all
dimensional measurements of the structures and all other information relating to them as revealed
and obtained during their work and have such measurements and information duly endorsed by the
Project Manager at site. The work shall not start unless full measurement is recorded by the Project
Manager. In some special cases, however, the recording may be done after dismantling.

The salvaged materials before or after dismantling shall be immediately measured and recorded in
presence of the Project Manager and shall be in the custody of the Contractor until instructed to be
disposed of by the Project Manager. Any loss of any dismantled material shall be recovered from
the Contractor's bill at the recovery rate.

380
5.4 Site office Facilities for the Project Manager and his Staff

Description

The Contractor shall provide and maintain temporary site office facilities during the construction
period for the Employer and Consultant.

5.5 Earth Work in Excavation for Structure

Description

The item shall consist of setting out true lines to all foundations for structures, performing the
excavations to the required levels and grades in any kind of soil encountered, removing the spoils
and backfilling of original ground line as provided in these specification or as directed by the
Project Manager.

Construction Requirements

The Contractor shall comply with all safety regulations and shall furnish, erect and maintain
suitable barricades and warning signs and take such other measures as necessary to prevent
personal injury or property damage.

5.5.1 Earth Filling

Description
The item shall consist of filling any place or area, to make up levels, according to these
Specifications and Plans with specified earth materials.

Construction Requirements
Silty Sand or other approved materials, free from large lumps, organic or other extraneous
materials, shall be used for fill. Materials from excavation on the sites may be used as ordinary fill
if it is approved.

The fill materials shall be deposited and spread in successive uniform horizontal layers of about
150 mm thick and compacted by use of mechanical 1.5 ton “Vibro” compactor or other approved
devices to a 98% standard dry density in road and pavement sub-base and 95% standard dry density
for other area.

Tests shall have to be carried out at recognized laboratory to ascertain the nature of the fill material
and the degree of compaction obtained for the filled material for which samples have to be taken
and transported by the Contractor at his expense and as directed by the Project Manager.

5.5.2 Sand Filling

Description

The item shall consist of filling any place or area, to make up levels, according to these
Specifications and Plans with specified and approved materials.

381
Construction Requirements:

Silty Sand or other approved materials, free from large lumps, organic or other extraneous
materials, shall be used for filling Materials from excavation on the sites may be used as ordinary
fill if it is approved.

Materials
Fineness modulus not less than 1.0 shall be clean and free from organic and other deleterious
materials

The fill materials shall be deposited and spread in successive uniform horizontal layers of about
150rnrn thick and compacted by use of mechanical 1.5 ton “Vibro” compactor or other approved
devices to a 98% standard dry density in road and pavement sub-base and 95% standard dry density
for other area. In filling /back filling against a newly constructed structure precaution must be taken
so that the structure is well matured to take the thrust of filling and while filling that against a wall,
the filling is done from both sides simultaneously.

Tests shall have to be carried out at recognized laboratory to ascertain the nature of the fill material
and the degree of compaction obtained for the filled material for which samples have to be taken
and transported to the recognized laboratory by the Contractor at his expense and as directed by the
Project Manager.

5.6 Brick Flat Soling (BFS)

Description

The item shall consist of supplying and laying bricks on top of the earth or sand bed to form a sub-
base.

Construction Requirements

Bricks shall comply with requirements of First Class bricks. The binding sand shall have a
minimum Fineness Modulus of 1.0 and shall be clean, and free of any organic matters.

Bricks shall be laid flat in surface to surface contact with adjoining bricks and their joints shall be
filled with sand. The sand shall be brushed in until the joints are filled. Flushing in of sand with
water shall not be done unless permitted. Bricks shall not be laid on the floor or foundation bed
until the floor or foundation bed is inspected and approved by the Project Manager.

In case of Multi-layer Soling, care shall be taken to stagger or "break" all joints in placing
subsequent courses of soling. No brick shall be laid on loose earth or earth filling which are not
compacted to the desired degree.

5.7 Lean Cement Concrete (CC) Works

The specification shall be the same as for RCC works excepting that:
(i) No reinforcement shall be used;
(ii) Proportion shall be as noted in Schedule of Items;
(iii) 12 mm downgraded chips of Jhama bricks /Boulder shall be used as coarse aggregate as
specified in Schedule of items;

382
 (iv) The curing shall be done for 7 days minimum;
(v) Compaction of concrete may be done by wooden or steel tempers or rammers in lieu of
vibrators.
In order to improve bond with masonry/concrete work coming above it, if required, the surface
shall be roughened before it reaches initial set, by scouring with the help of a pointed tool.

5.8 Cement Concrete in Floor

Description

The work covered by this item shall consist of constructing in floor or elsewhere, 75mm or 38mm
thick cement concrete with 1:3:6 mix of cement, sand of FM 1.2 and 12mm downgraded bricks or
stone chips as specified in schedule of items.

Construction Requirements

Construction shall be carried out as per requirements of drawing.

5.9 Damp Proof Course

Description

The work covered by this item shall consist of constructing, on top of foundation walls or
elsewhere 75mm/ 38 mm thick artificial stone with a 1:1.5:3 mix of cement, sand of FM 2.5 and 12
mm downgraded crushed stone chips and finishing with a coat of bitumen as per instruction of the
Project Manager.

Construction Requirements

Damp-proof course shall extend the full width of the plinth walls unless otherwise required by the
plans and shall be laid only after the levels of the plinth have been checked.

5.10 Reinforced Cement Concrete Work (RCC)

Description
This item shall consist of manufacturing concrete as provided in these Specifications and
construction where required, and of the form, dimensions and design shown on the plans.

Construction Requirements
Concrete shall consist of a mixture of Portland cement, fine and course aggregate and water. The
proportions in which the various ingredients shall be used in the concrete mix for various work,
shall be designed in accordance with the specified strength and suitable workability.
Material shall conform to the requirements specified below and in the relevant sections Material
Specifications.
Construction shall be according to these specifications. Contractor shall follow the following
standards of American Society of Testing Materials along with the Building Code Requirements for
Reinforced Concrete ACI 318-89 for Specification not covered in these Specifications. In case of
differences between specifications contained in this book and those of ASTM or ACI, the
specifications specified in this book shall stand.

383
Cement

"Specification for Ordinary Portland Cement" (Type-I) - ASTM C150 or BS12

"Specification for Concrete Aggregates" - ASTM C 33
"Standard Method of Making and curing concrete Test Specimen in - ASTM C31-89
the field"
"Standard Method of Test for compressive strength of cylindrical - ASTM C39-86
concrete Specimens"
"Standard Method of Sampling Fresh Concrete" - ASTM C172-90
"Standard method of Making & Curing concrete Test Specimens in - ASTM CI92-90
the laboratory"
"Standard method of obtaining and Testing Drilled Cores and Sawed
- ASTM C42-90
beams of Concrete"
"Standard Specifications of Chemical admixtures in concrete"
- ASTM C494
Cement shall be Portland Cement Type-I, ASTM
- ASTM C150

Portland cement to be normally used shall conform to ASTM specification C-150 type-l or BS-12.
It shall be free from any hardened lumps and any foreign material other than the manufacturing
ingredients. Cement shall have a minimum 90% of particles by weight passing the 75 micron sieve.
Cement shall have an initial setting time in excess of 30 minutes and final setting time not longer
than 7 hours. The Project Manager reserves the right to reject any cement that fails to achieve
specified concrete strength as per proportion of materials laid down in the schedule of items.

Only approved brand, grade or kind of cement shall be used in a given structure above the ground
level specially, for fare face finished concrete, tiles works etc. except upon the written permission
of the Project Manager of other used.

The Contractor shall be responsible for the proper storage of the cement at the job site. Cement
shall be stored in an air tight waterproof shaded area having damp proof floor, waterproof walls and
leak proof roof. The cement stacks shall be placed at a minimum distance of 300 mm from the
walls. The damp proof floor shall be constructed by raising it minimum 300 mm above the ground.
If the cement is damaged and becomes lumpy due to defective storage, it shall be removed from the
job site within 24 hours of receipt of instructions from the Project Manager.

Cement may be measured by weight of in a standard bag to weigh 1 cwt or 112 pounds/50kg
having a volume of 0.0354 cum or 1.25 cft. The Contractor shall maintain the record of deliveries
of cement to the site and its use in the work.

Fine Aggregate (Sand)

Fine Aggregate shall consist of well-graded clean natural sand, free from injurious amount of
organic impurities and deleterious substances and shall have a fineness modulus of not less than
2.50. Fine aggregate shall be well graded from coarse to fine and when tested by means of
laboratory sieves shall conform to the following requirements:

384
 Sieve Mass
Percent passing
9.5 mm (3/8 in 100
4.75 mm (No.4) 95 - 100
1.18 mm (No. 16) 45- 80
0.300 mm ( No. 50) 10 – 30
0.150 mm (No. 100) 2 -10

Coarse Aggregate

Coarse Aggregate shall consist of well-graded broken or crushed first class jhama bricks or boulder
chips as specified on the structural drawings and/or BQ and shall be free from any adherent
coatings.
Grading of Coarse Aggregates

Coarse aggregate shall be well graded, between the limits specified and the size or sizes designated
shall conform to the requirements given in the following tables or otherwise specified or directed
by the Project Manager.

Percentage by weight passing US Standardsieves having square

Designated sizes openings
38 mm 25 mm 20 mm 12 mm 10 mm No.4 No.8
25 mm down graded 100 95-100 -- 25-60 -- 0-10 0-5
20 mm down graded ---- 100 90-100 -- 20-55 0-10 0-5
12 mm down graded -- 100 90-100 40-70 0-15 0-5

Delivery and Storage of Materials:

a. Cement

In transit and storage or stock-piled at site shall be protected from dampness or any damage
by climatic conditions that would change its characteristics or usability. Cement at site shall
be stored in dry weather proof godowns (or shed) built at the cost of the Contractor. Cement
must not be stacked in more than l0 bag height. Sufficient space shall be provided for
circulation and rotation of bags in order to minimize the length of storage of any of the
bags. The floor of the godown shall consists of wooden planks resting on base prepared of
dry bricks laid on edge. Batches of cement shall be used for the work in the order in which
they are delivered to the site. A register shall be maintained by the Contractor listing date of
delivery and quantity of each consignment for easy identification.
b. Aggregates
Aggregate shall be stock-piled at least 7 days prior to their anticipated use to permit the
Project Manager to sample each stockpile to determine the acceptability of the material for
the intended use.
Aggregates of different sizes or grades and from different sources of supply shall not be
mixed. All aggregate shall be stored free from contact with earth and other deleterious
matter.

385
 Every precaution shall be taken during transport and stockpiling of coarse aggregate to
prevent segregation.

Segregated aggregates shall not be used until they have been thoroughly remixed and the
resultant pile is of uniform and acceptable grading at any point from which a representative
sample is taken.

Composition of Mix

The strength requirement and workability shall govern the mix proportion for each class of
concrete:

Proportion of 28 day Place of Use Aggregates Min.

concrete cylinder Cements
crushing per m3
strength Fine Coarse (50 kg bag)
(min.)
(1:1.5:3) 21 MPa In footing, water Sand 20 mm down 8.0 bags
tank, column, slab, FM 2.5 graded stone chip
beam, stair lintel and
all
other RCC works
like switch yard
foundation
(1:1.5:3.0) 20 MPa In Damp Proof Sand 12 mm down 8.0 bags
Coarse FM 1.2 graded stone chip

(1:2:4) 18 MPa In all RCC works Sand 20 mm down 6 bags

in Ancillary FM 2.5 graded picked
Structures & 1.5 jhama chip'
(1:3:6) 15 MPa In bellow foundation Sand 20 or 12 mm 4.5 bags
and FM 1.5 downgraded
Floor(C.C) picked jhama
chips

Slump Slab, Beam, Columns etc. -50mm.

Trial mixes for every class of concrete with representative materials from site shall be prepared by
the Contractor and carried to the laboratory in accordance with approved procedure. The nominal
strength in these tests shall exceed the specified minimum strength by at least 20%. No concrete
shall be placed in the permanent works until the relevant mix has been approved by theProject
Manager.

Batching

The Contractor shall provide and maintain in good order suitable measuring equipment and devices
required to determine and control accurately the relative amounts of various materials entering the
mix. All measurements shall be by weight/volume and shall be accurate within a tolerance of 1 %
for each batch. If the measurements are by volume then standard wooden boxes shall be used.

386
a. Cement

Unless an integral number of bags, as packed by the manufacturer is used, the Cement shall be
weighed. A bag of cement weighing 50 kg net shall be considered as 0.035 m3

b. Aggregates

Different types and sizes of aggregates shall be batched separately by weight/volume.

c. Water

The amount of mixing water shall be weighed/measured, allowance being made for the quantity of
the free water contained in the aggregates. Water cement ratio shall be decided for every class of
concrete and according to the place of use. The water/Cement ratio shall not exceed 45% by weight
for all type of concrete.

Sufficient acceptable materials shall be available at the batching site to ensure continuous
placement necessary for structures. The moisture content of the accepted aggregate shall remain
consistent to the extent that the resultant successive batches of concrete do not vary in consistency
by more than 6 mm of slump. If the moisture content in the aggregate varies by more than the
above tolerance, corrective measures shall be taken to bring the moisture to a constant and uniform
quantity before any more concrete is placed.
Coarse aggregate shall be saturated with water at least 12 hours before use to prevent absorption of
the mixing water.

MIXING OF CONCRETE

a) Machine Mixing:

Concrete shall be mixed in concrete mixer of approved type and appropriate capacity.
Each batch shall be thoroughly mixed for a period of not less than 2 minute after all materials
including the water are in the drum and during this period the drum shall be in the mixing position
and revolve at uniform rate of not less than 14 or more than 20 revolutions per minute. The cement
and sand shall be thoroughly mixed in dry condition.

The batch shall be so charged into the mixer drum that some water shall enter in advance of the
cement and aggregate. The entire content shall be removed from the drum before the succeeding
batch is placed.

Concrete shall be mixed in quantities required for immediate use. Concrete shall not be used which
has developed initial set or which is not in place within thirty (30) minutes after the water has been
added. Re-tempering of partially hardened concrete by remixing with or without additional
materials or water, or by other means shall not be permitted. The inside of the mixing drum shall be
kept free of hardened concrete at all times.

Mixers which have been out of use for more than 30 minutes shall be thoroughly cleaned before
any fresh concrete is mixed. Unless otherwise agreed by the Project Manager, the first batch of
concrete through the mixer shall contain only two thirds of the normal quantity of coarse aggregate.
Mixing plant shall be thoroughly cleaned before changing from one type of cement to another.

387
b) Hand Mixing:

Hand mixing shall not be permitted except for unimportant structural members and only at the
discretion of the Project Manager. When hand mixing is permitted it shall be taken to ensure that
the mixing is continued until the mass is uniform in colour and consistency. If hand mixing is
permitted by the Project Manager, the Contractor shall use l0% extra cement for hand mixing for
which no extra payment will be made.

Consistency of Concrete

The consistency of concrete shall be determined following evaluation of the placement conditions
for each individual section of the work but in no case the slump shall exceed 62mm unless
otherwise decided. Mix proportions and consistency shall produce a dense, well compacted
concrete with a minimum tendency to segregate under placing conditions, free from sand streaks,
honeycomb, air-pockets, exposed reinforcing steel and other forms of structural weakness or
unsatisfactory appearance.

Transport and Placing

Concrete shall be so transported from the mixer and placed in the form that contamination,
segregation or loss of the constituent materials does not occur. Before placing the concrete, all form
work, space and the reinforcement contained in it shall be thoroughly cleaned .of all extraneous
matter. Care shall be taken to fill every part of the forms, to work the coarse aggregate back from
the face so that sufficient mortar shall be flushed from the mass to form a smooth surface, and to
force the concrete under and around reinforcing bars without displacing them.

The concrete shall be deposited in the forms in horizontal layers to a depth not exceeding 300 mm
and each layer shall be properly vibrated before laying the next one.

The concrete shall not be dropped freely from a height exceeding 1.0 meter nor shall it be deposited
in large quantities at any point. In columns of structures special tremie pipe may be used for drop
more than 1.8 meters. Dragging of concrete inside the forms or distribution by vibrators or allowing
it to flow by gravity to the ends of the forms shall not be permitted.

In sections where it is extremely difficult, to place concrete containing the larger sizes of the coarse
aggregate, a modified mix, as approved by the Project Manager, may be used to ensure against
honeycomb and separation of the coarse aggregate from the mortar. Concrete shall be deposited
and compacted in its final position within 30 minutes of its discharge from the mixer and shall not
be subjected to vibration between 2 and 24 hours after compaction. When in situ concrete has been
in place for 4 hours no further concrete shall be placed against it for a further 20 hours.

Compaction

Concrete, during and immediately after placing, shall be thoroughly compacted by mechanical
vibration. The vibration shall be internal unless otherwise authorized by the Project Manager.

Vibration shall be of a type and design approved by the Project Manager. It shall be capable of
transmitting vibration to the concrete at frequencies of not less than 4,500 impulses per minute.

The intensity of vibration shall be such as to visibly affect a mass of concrete of one inch slump
over a radius of at least 450 mm.

388