TECHNICAL SPECIFICATIONS
FOR
66 kV CURRENT TRANSFORMER
&
66 kV POTENTIAL TRANSFORMER
Page 1 of 33
Technical Specification of 66 KV CT/PT
TECHNICAL SPECIFICATION
FOR
66 kV CURRENT AND VOLTAGE
TRANSFORMERS
SECTION – I
1.1 GENERAL DESIGN FEATURES OF CURRENT TRANSFORMERS:
1.1.1 This section covers the design, manufacture, assembly, testing at manufacturer’s
works, supply and delivery of outdoor, dead tank type, oil impregnated
paper, single phase, 50 Hz, oil immersed, self cooled, current transformer
suitable for operation in the climate conditions specified. The current
transformers shall be complete in all respects.
1.1.2 STANDARDS:
1.1.2.1 CURRENT TRANSFORMERS:
SR. STANDARD NO. TITLE
NO.
1 IS:2165 Insulation co-ordination for equipment of 100 KV and
above
2 IS:2705 (I to IV) Instrument Transformers
3 IS:2099 High voltage porcelain bushings
4 IS:3347 Dimensions of porcelain transformer bushings
5 IS:2071 Method of high voltage testing
6 IS:335 Insulating oil for transformers and switchgears
7 IS:2147 Degree of protection provided by enclosures for low
voltage switchgear and control.
8 IEC-60044-1 Instrument Transformers
9 IEC-270 Partial discharge measurement
10 IEC-44(4) Instrument transformer measurement of PDs
11 IEC-171 Insulation co-ordination
12 IEC-60 High voltage testing techniques
13 IEC-8263 Method for RIV test on high voltage insulators
14 -- Indian Electricity Rules 1956
1.1.2.2The Instrument Transformers covered by this specification shall comply with
the requirement of the latest edition of IEC Publication No. 60044-1&/ or Indian
Standard No. 2705 Parts – I to III (as amended up to date) but the Instrument
Transformers for the accuracy class ‘PS’ shall confirm to Part - IV of IS : 2705
except where specified otherwise in the specification.
1.1.2 The core shall be high grade, non – ageing, silicon laminated steel of low
hysteresis loss and high permeability. The core material used in case of
metering core shall be stated.
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Technical Specification of 66 KV CT/PT
1.1.3 The current transformers shall be hermitically sealed to eliminate breathing and
entering of air and moisture in the tank. Provision of pressure releasing device is
not permitted.
For compensation of variation in volume of oil due to temperature variation,
stainless steel bellows shall be provided. The successful bidder shall have
to submit calculations of volumetric expansion and contraction. These
calculations shall be submitted along with the basic parameters of SS bellow used
in CT.
Rubber bellow or Nitrogen gas cushioning for above purpose shall not be
permitted.
The current Transformers provided with stainless steel bellows for compensation
of oil volume variation shall be provided with a suitable oil level indicator at
suitable location to enable an observer to see the oil level of the C.T. from the
ground level. Oil level indicator shall be provided with fluorescent green coloured
floating ball of non oil reacting material.
All parts of bellow shall be of stainless steel only.
1.1.4 The core of current transformers to be used for metering and instrumentations
shall have saturation factor, low enough to avoid damage to the instruments, in the
event of maximum short circuit current.
1.1.5 The C.T. core, to be used for protective relays shall be of accuracy class,
specified or appropriate class suitable for back up, over current and earth fault,
differential and bus-bar protection.
1.1.5 The successful bidder shall give assurance for trouble free and maintenance free
performance for a period of 36 months from the date of commissioning; during
which period, the CTs shall be repaired / reconditioned / replaced free of cost,
immediately in case of any trouble. Therefore, the successful bidder shall
ensure that sealing of current transformer is properly achieved. In this
connection, the arrangement provided by the successful bidder at various
locations including the following ones shall be described supported by sectional
drawings.
i) Location of emergence of primary and secondary terminals.
ii) Interface between porcelain housing and metal tank.
iii) Cover of the secondary terminal box.
iv) G.A. drawing complete with details of primary and secondary windings
overall dimensions, weight, nameplate, porcelain insulator, primary &
secondary terminals, terminal connectors, etc.
1.1.5 Nuts and bolts (or screws used for fixation of interfacing porcelain bushings for
taking out terminals) shall be provided on flanges, cemented to the bushing and
not on the porcelain i.e. Flange type 66 KV bushing for CT, shall be provided.
1.1.5 For gasket joints, wherever used, Nitrile Butyl rubber NBR/Viton shall be
used. No CORK gaskets shall be used. All gaskets/O rings shall be
fixed in a machine groove. The gaskets shall be securely fitted for
perfect sealing.
1.1.5 The bolts required for fitting the dome shall be of stainless steel of minimum 6
mm dia.
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Technical Specification of 66 KV CT/PT
1.1.5 The outer surface of metal tank shall be Hot Dip Galvanized, whereas, the inner
portion shall be painted with oil resistive, insoluble paint. The JKPDD reserves
right for stage inspection during manufacturing process of tank / CT. The
galvanizing shall be as per applicable standard IS:2629 and
minimum thickness of zinc coating shall be 610 gm/sqmt.
1.1.5 The tank of CT shall be provided with pressboard of 2 mm thickness inside and at
bottom.
1.1.5 Provision of drain valve for sampling / draining of oil purpose at the bottom of
tank is not permitted.
1.1.5 The minimum thickness of flange & gasket provided on tank shall be as follow:
a) Flange thickness of tank - 8 mm
b) Top plate thickness - 5 mm
c) Gasket thickness - 6 mm
1.1.5 The current transformers shall be suitable for mounting on steel structures or
concrete pedestals.
1.1.6 WINDING AND TERMINALS:
1.1.6.1 The rating of the secondary winding shall be as specified under Section II of this
specification. Ratio changing arrangement shall be provided on secondary
winding for multi–ratio design, either a number of identical secondary winding
may be provided to achieve desired ratios by series / parallel connection for the
secondary winding or the secondary winding may be tapped. However, identical
secondaries for tapped secondary winding shall meet requirement as specified.
1.1.6.2 Primary and secondary windings shall be of electrolytic grade copper and shall
have continuous thermal rating as specified for all ratios. The primary winding is
to be designed for continuous extended primary current at 120 % of rated primary
current. The secondary winding wherever tapped, shall be adequately reinforced
to withstand normal handling without damage.
1.1.6.3 The primary terminals shall be of standard size of 30 mm dia x 80 mm length for
all CTs rated up to 1200 Amps. For higher values of primary current, each primary
terminal shall be made out of two such rods of 30mm dia x 80 mm length in
parallel. The primary terminals shall be of heavily tinned electrolytic copper. The
maximum thickness of tinning shall be 15 microns.
1.1.6.4 The secondary terminals shall be brought out in a compartment for easy access.
Secondary terminal studs shall be provided with at least three nuts and adequate
plain and spring washers for fixing the leads. The studs, nuts and washers shall
be of brass, duly nickel-plated. The minimum outside diameter of the studs shall
be
6mm. The length of at least 15mm shall be available on the studs for inserting the
leads. The horizontal spacing between centers of the adjacent studs shall be
at least 1.5 times the outside circum dia. of the units.
1.1.6.5 The current transformer shall be provided with suitable test tap for measurement
of capacitance, tan delta as well as partial discharges, in factory as well as at
site. Provision shall be made of a screw on cap for solid and secured earthing
of the test tap connection, when not in use. A suitable caution plate shall be
provided duly fixed on the cover of the secondary terminal box, indicating the
purpose of the test tap and necessity of its solid earthing as per prescribed
method, before energizing the CT.
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Technical Specification of 66 KV CT/PT
1.1.7 TERMINAL BOX OF CURRENT TRANSFORMERS:
1.1.7.1 The exterior of the secondary terminal box shall be hot dip galvanized. A cable
box along with necessary glands for receiving control cables suitable for mounting
on bottom plate of the terminal box shall be included in the scope of supply. A
door with locking arrangement shall be provided on the front of the terminal box.
The secondary terminals shall be taken out through composite epoxy or FRP
mould having single gasket packing & shall be provided by suitable link with
dummy secondary leads. For control cable connections, separate terminal
connector block to be provided. Secondary jumpers shall be terminated at one
side of this terminal connector block. The secondary terminal box shall
comply with Degree of Protection (IP-55) standards and type test
report shall be furnished with technical bid.
1.1.8 TEMPERATURE RISE:
1.1.8.1 The maximum temperature rise of the current transformer and its oil, winding and
external surface of the core and other parts shall be as specified in Table I of IS:
2705 (Part I) 1981.
1.2 BUSHING AND INSULATORS:
1.2.1 The porcelain hollow insulator used shall be homogenous, free from lamination
cavities and other flaws or imperfection that might affect the mechanical or
dielectric qualities. The hollow insulator shall conform to the latest edition of IS:
5621. The puncture strengths of the hollow insulator shall be entirely free
from external and internal corona. The total creepage distance of the hollow
insulator shall be 1810 mm (minimum).
Suitable means shall be provided to accommodate conductor expansion and
there should not be any undue stress on any part of the equipment due to
temperature changes.
Packing may be provided between insulator and tank. This packing shall be
preferably Nylon Bush of minimum 3 mm thickness.
The exterior, upper and lower joints of insulator bushing shall be sealed with
suitable sealant.
1.2.2 The hollow porcelain bushings conforming to the latest edition of IS: 5621 shall
be used for current transformers. The insulation of bushings shall be coordinated
with that of the instrument transformer such that the flashover, if any, will occur
only external to the current transformers. The bushings should not cause radio
interference, when operating at rated voltage.
1.2.3 The quantity of insulating oil for the first filling of oil in each CT and the
complete specifications of the oil shall be stated. The oil shall conform to the
requirements of latest edition of IS: 335. The actual oil to be used shall be of the
following approved make.
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Technical Specification of 66 KV CT/PT
The manufacturer of CT shall measure the PPM value of oil before filling inside the
CT and shall keep record of the same.
1.3 TERMINAL CONNECTORS AND EARTHING TERMINALS:
1.3.1 Compression joint type bimetallic terminal connectors suitable for ACSR
‘PANTHER’ conductors (with 510 amps.) shall be supplied for CTs.
The terminal connectors shall be suitable for 31.5 KA for 3 sec. They shall be suitable
for vertical & horizontal connections of the transmission line conductors or station bus
bar. The bolt and nuts shall be of stainless steel and one SS washer and two SS nuts
(including lock nut) for each bolt shall be supplied. Two grounding terminals suitable
for receiving connections for grounding shall be provided for the current transformers.
1.4 GALVANIZING:
All ferrous parts of current transformers including bolts, nuts etc. shall be hot dip
galvanized as per IS: 2629 – 1966 with (latest edition) and the minimum thickness of
zinc coating shall be 610 gr/sqmt.
1.5 TESTS AND TEST REPORTS:
1.5.3 Reports of all type tests as stipulated in the latest edition of IS:2705 & IEC
60044-1 for current transformers shall be submitted by the successful bidder.
1.5.2 The type test reports for the type tests carried out as per IS: 2705 (latest edition) &
IEC 60044-1 for specified CTs and those for offered insulators shall be
submitted. The type test reports shall not be older than seven years and shall
be valid up to expiry of validity of offer.
Following test reports shall be submitted.
1. Lightning chopped Impulse voltage withstand test on
Primary winding
2. High voltage power frequency wet withstand test on
Primary winding
3. High voltage power frequency dry withstand test on primary winding
4. Temperature rise test
5. Short Time Current withstand test
6. Determination of Errors & other characteristics
7. Measurement of dielectric dissipation factor
8. Degree of protection IP55 for secondary terminal box
9. STC test on primary terminal connector
10 Mechanical Load test on primary terminal
11 Thermal stability test
12 Thermal coefficient test
The type test reports for offered terminal connectors (confirming to IS: 5561
(latest edition), but not older than seven years prior to the date of bid opening and
those for offered insulators confirming to the applicable standard shall also be
submitted.
IMPORTANT NOTE: In case of non-submission of some of the type test reports, the
successful bidder shall submit the same before commencement of supply, without affecting
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Technical Specification of 66 KV CT/PT
delivery schedule, from NABL accredited laboratory, free of cost.
If successful bidder has submitted all valid type / special / additional test reports as per
requirement of technical specifications then the same are not required to be repeated.
However, those tests which are covered under acceptance/ additional/ routine tests will be
required to be carried out during the inspection.
1.5.3 Routine tests as per the latest edition of IS: 2705 for current transformers shall be
carried out on each current transformer (in presence of purchaser’s representative, if
desired by the purchaser).
Following tests shall be performed:
1. Verification of terminal marking and polarity
2. High voltage power frequency dry withstand test on primary winding
3. High voltage power frequency dry withstand test on secondary
winding
4. Over Voltage inter turn test
5. Measurement of Partial Discharge test
6. Determination of Errors & other characteristics
7. Measurement of dielectric dissipation factor (0.3% max) &
Capacitance at 10 kV and at Um/3.
8. Temperature Rise test (On any one unit from offered lot)
1.5.4 General points:
a) The manufacturer shall use 5 KV motorized megger for measuring IR valves of
CTs.
b) The manufacturer shall carry out Partial Discharge test and tan delta test as per
relevant ISS, and shall keep record of the same.
c) If so required, the purchaser shall select one CT of each ratio from the first lot or
any subsequent lot of CTs, which shall be type tested in presence of purchaser’s
representative at third party Govt. recognized laboratory. The balance CT from
the first offered lot or any subsequent lot shall be inspected and tested for routine
tests.
d) The manufacturer shall offer CTs for routine tests / inspection. Record of
each manufacturing process shall be maintained by the manufacturers,
and shall be shown to the inspector, on demand at the time of inspection.
1.5.5 ADDITIONAL ACCEPTANCE TEST:
1.5.5.1 In addition to the acceptance tests indicated in IS-2705 (with latest amendment),
the successful bidder has to conduct following tests on all offered lot of CTs
during inspection:
a) Tan Delta test (0.3% Max) (On all units) (at 10 kV & Um/3)
b) Measurement of Capacitance test (On all units) (at 10 kV & Um/3)
c) Temperature Rise test (On randomly selected one unit)
d) Partial Discharge test (<10 pC) (On selected unit for (c), but to be
carried out before and after
Temperature Rise test)
e) Tests on Oil:
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Technical Specification of 66 KV CT/PT
i) BDV test ] On randomly selected unit of first lot
ii) Tan Delta test ] offered for inspection and to be
iii) Water PPm test ] conducted after HV test only.
iv) Resistivity at 90 0
] v) Viscosity ]
vi) Total acidity ]
iv) DGA test Copy of test report, received from the
power oil manufacturer, to be submitted.
(NOTE: If the supplier of oil is changed during execution of order, same test
shall be repeated for the oil of new supplier.
f) Thermal stability test on CT (On any one unit)
g) Thermal coefficient test on CT (On any one unit)
1.5.6 All the tests reports and oscillograms shall be submitted and got approved from the
purchaser before dispatching the equipment.
1.6 QUALITY ASSURANCE PLAN:
The successful bidder shall furnish following information. Information shall be
separately given for individual type of instrument transformer.
i) Statement giving list of important raw materials, including but not limited to
a) Primary Conductor
b) Insulator Bushing
c) Core
d) Oil
e) Sealing material
f) Secondary wire
Names of sub-suppliers for the raw materials, list of standards; according to which the
raw materials are tested, list of tests normally carried out on raw materials in
presence of successful bidder’s representative, copies of test certificates.
ii) Information and copies of test certificates as in (i) above, in respect of,
bought out accessories
iii) List of manufacturing facilities available. In this list the successful bidder
shall specifically mention whether lapping machine, vacuum drying plant,
air conditioned dust free room with positive air pressure for provision of
insulation, oil leakage testing facility, facility for testing tan delta of insulation
at rated voltage etc. are available.
iv) Levels of automation achieved and list of areas where manual processing
still exists.
v) List of areas in manufacturing process, where stage inspections are normally
carried out for quality control and details of such tests and inspections.
vi) Special features provided in the equipment to make it maintenance free.
vii) List of testing equipment available for final testing of instrument transformer.
viii) The following testing equipments shall be available for testing
1) Partial Discharge test set up
2) Tan delta and capacitance test set up
3) Minimum Sensitivity of high voltage laboratory-
2.5pC for PD measurement. This is to be demonstrated
before test.
All test set up shall be calibrated at NABL accredited
laboratory and report shall be submitted with inspection report.
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Technical Specification of 66 KV CT/PT
1.7 Guaranteed and technical particulars as called for in attached Appendix –I shall be
furnished.
1.8 COMPLETENESS OF EQUIPMENTS:
Any fittings, accessories or apparatus which may not have been specifically
mentioned in these specifications, but which are usual or necessary for the
equipment of similar plant shall be deemed to be included and shall be supplied by
the contractor without extra charges. All plant and equipment shall be complete in all
details whether such details are mentioned in the specification or not.
1.9 INSPECTION:
i) The purchaser shall have access at all times to the works and all other places of
manufacture, where the Instrument Transformers are being manufactured and
the supplier shall provide purchaser’s representative all facilities for unrestricted
inspection of the works, raw materials, manufacture of all the accessories and for
conducting necessary tests.
=
ii) The successful bidder shall submit the stage wise inspection program.
Stages of inspection and owners participation would be defined and tied up
at the time of award of contract.
iii) During inspection all the acceptance tests as indicated at respective clause
under head of ‘Acceptance tests’ along with additional Sealing test as
detailed here under, shall be carried out before temperature coefficient
test.
Sealing test shall be carried out on one randomly selected unit out of every
20 or less offered quantity. In the event of failure of unit during sealing test
next unit will be randomly selected from the offered lot. Failed unit shall not
be accepted. If second unit also fail to clear Sealing test WHOLE lot shall be
rejected.”
SEALING TEST PROCEDURE:
(i) Test shall be performed on completely assembled unit.
(ii) Test shall be performed during acceptance test on one randomly
selected unit.
(iii) Temperature of CT/PT under test will be elevated and maintained at
50 (oC) and simultaneously it shall be subjected to internal
pressure of 103 kPa (@1.1 kg/sqcm) for 12 hrs.
(iv) Arrangement shall be made by manufacturer to maintain required
pressure and temperature for 12 hrs.
(v) During and after the test, there shall not be any oil leakage from any
part or joint of CT/PT.
Readings of temperature, internal pressure applied and duration test along
with observation of leakage, if any, shall be noted in inspection
report.
iv) Sealing test is applicable to each lot of each class and each ratio even if the
design is same.
v) No material shall be dispatched without Inspection.
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Technical Specification of 66 KV CT/PT
vi) The acceptance of any quantity of the equipments shall in no way, relieve the
successful Bidder of his responsibility for meeting all the requirements of this
specification and shall not prevent subsequent rejection, if such equipments are
found defective later.
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Technical Specification of 66 KV CT/PT
TECHNICAL SPECIFICATION FOR
66 kV CURRENT AND VOLTAGE TRANSFORMERS
SECTION – II
TECHNICAL REQUIREMENTS FOR 66 kV CURRENT TRANSFORMERS
2.1 SCOPE:
2.1.1 This section covers the specific technical requirements, and systems particulars for
which current transformers shall be offered as per the general technical requirements
given under section – I of this specification.
2.1.2 All equipments offered shall be suitable for continuous satisfactory operation at the
extended primary current of 120 % of full rated capacity, under the above climatic
conditions.
2.2 SYSTEM DETAILS:
i) Nominal system voltage 66 KV
ii) Maximum rated voltage 72.5 KV
iii) Minimum rated voltage 60 KV
iv) Frequency 50 Hz.
v) Number of phases 3
vi) Neutral earthing Solidly Earthed
2.3 TYPE & RATING OF CURRENT TRANSFORMERS
i) CT Ratio 300-150/1-1-1A
ii) Core 3
iii) Purpose Core –1 Metering
Core –2 Relaying
Core –3 Differential
iv) Rated burden (VA) 15 (Core –1)
(Lowest Ratio) 15 (Core –2)
(at minimum tap) (Core –3)
v) Class of accuracy 0.5 (Core-1)
5 P (Core-2)
P S (Core-3)
vi) i) Rated accuracy limiting factor ALF 10 at minimum ratio for all 66
KV CTS
ii) Instrument security factor. (ISF) 5 or less at minimum ratio for all
66 KV CTS
vii) Minimum knee point voltage 650 V
(at highest ratio)
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Technical Specification of 66 KV CT/PT
