EE405- Electrical System Design

Module-3

Prepared by
Rajesh P
Assistant Professor
Nehru College of Engineering and Research Centre
Pampady, Thrissur
 Module-3
1.Industrial installations
2.Classifications
3. Design of distribution systems with light power
and motor loads for small and medium industries
4. Selection of transformer substations
5. Selection of switch gears and protective devices
6. Design of indoor and outdoor 11kV substations
up to 630 kVA
 Industrial Installations

1. More sophisticated installation

2. Take care of diverse load requirement in economic manner

3.Preserving safety and reliability with electrical installations

4.Easiness of maintenance and fault location features

5.Energy conservation
 Classification of Industrial Buildings

(A) Fire hazard

(B) Power Consumption

(C) Pollution hazard

 (A) Classification based on fire hazard
(i) Group G1- Building used for low fire hazard
industries

Operation/process conducted in those

buildings, there are no possibilities of self
propagation of fire to occur. Only effect of fire
from external sources.

E:g; Cement factories, Glass factory, Rice mill,

Soap and detergent factory etc.
(ii) Group G2- Building of moderate fire hazard
In this type, operation/process are
liable to give rise to fire that will burn with
moderate rapidity, produce considerable
volume of smoke or non-toxic fumes and will
not result in an explosion

E:g; Ship repairing docks, coir industry,

chemical manufacturing, flour mill etc
(iii) Group G3- Buildings with high fire hazard
In this type, operations/ process are
liable to give rise to a fire which will burn
with extreme rapidity, generate poisonous
fumes, lead to explosions.

E:g; Alcohol distilleries, explosive

manufacturing, fire work industries, oil
mill, petrochemical
 (B) Classification based on power consumption

(i) Light industries(Small)

(ii) Average industries (medium)

(iii) Heavy industries

Description Average power requirement Examples

Light industry Up to 50 kVA Hosiery, garment making,

ornament making etc

Average Industry above 50 up to 2000kVA Furniture pottery, glass,

tobaco, electrical gadgets,
textiles, engine fitting, light
processing etc.

Heavy industry above 2000kVA Heavy electrical quipment,

steel mills, foundaries, ship
building, chemical plants,
fertilizer plants, metal
extraction, petrochemicals,
paper mills etc.
 (C ) Classification based on pollution level
(i) Pollution degree 1
No pollution or only dry, non conductive
pollution occurs. The pollution has no
influence

(ii) Pollution degree 2

Only non-conductive pollution occurs
except that occasionally a tempory
conductivity caused by condensation is to be
expected.
(iii) Pollution degree 3
Conductive pollution occurs or dry non-
conductive pollution occurs which becomes
conductive due to condensation

(iv) Pollution degree 4

Continuous conductivity occurs due to
conductive dust, rain or other wet
conditions.
 Power distribution architecture of Industrial
Installation-Factors considering
1. Activity
2. Site topology
3. Layout latitude
4. Service reliability
5. Maintainability
6. Installation flexibility
7. Power interruption sensitivity
8. Disturbance sensitivity
1.Activity- The type of activity carried out in
the building. i.e; whether manufacturing,
food processing, logistics etc.
2. Site topology- Here consider the number
of buildings, number of floors in each
building, floor area. E.g; single storey or
multistorey or highrise buildings
3. Layout Latitude-Consider constraints in
terms of the layout of electrical equipment
in the buildings
Some parameters
▪ Aesthetics
▪ Presence of dedicated location
▪ Use of technical corridor(horizontal service
duct) per floor
▪ Use of technical service duct(vertical)

Three layout categories

Low- The layout latitude is low when the positions

of the electrical equipments are virtually imposed
on the building and cannot be changed to achieve
above said parameters
Medium- There is some flexibility in positioning the
electrical equipments.

High- Layout latitude is high if there is no constraints

in positioning the electrical equipment in the building
to satisfy the parameter mentioned above.

(4) Service reliability-

It is defined as the ability of the power supply
system to meet the supply function under
stated conditions for a specified period of time.
There are 3 categories of service reliability
(a) Minimum service reliability
(b) standard
(c) Enhanced service reliability

Service reliability will be minimum if the

installation is subjected to interruption related to
geographical(positioning of buildings with reference
to power production centre), technical(Power supply
through OH or UG or Ring system),
economic(Maintenance aspects)
Service reliability can be enhanced by taking
measures to reduce the power consumption
(5) Maintainability-During design stages
to limit the impact of maintenance on
the operation of the whole or part of the
installation.
Maintenance activity can be carried out
without disturbing the operation of the
production
(6) Installation flexibility
This is the possibility of easily moving of
power delivery points within the installation or
the facility to increase the power availability at
certain points.
• Non-flexible
• Design flexibility
• Implementation flexibility
• Operation flexibility
(7) Power interruption sensitivity
This is the capability of the process or system
to accept interruptions.
Sheddable loads-Possible to shut down a portion
of the load at any time
Long interruption acceptable loads-Accepting
interruption for more than 3 minutes
Short interruption acceptable-Accepting
interruption less than 3 minutes
No interruption acceptable- Power interruption
cannot be accepted
(8) Disturbance sensitivity- It is the ability of an
industry to work properly in the presence of
disturbance(over voltage, voltage distortion due
to harmonics, voltage fluctuations, voltage
unbalance).
It is classified as
Low sensitivity-very little effect on the
operation(e;g; heating devices
Medium sensitivity- a notable deterioration in
the operation (e;g; induction motors, lighting
loads)
High sensitivity- stoppage of operation(e;g; IT
equipment, sensitive instrument)
 Selection of Transformer Substation

▪ Consider economy of operation

▪ Technical suitability
▪ Cost
▪ Long term gains
▪ Transportation constraints
▪ Handling facilities
▪ Availability of supporting switchgear
Factors deciding selection of transformers
• Maximum demand

• Future expansion

• Spare capacity

• Statutory requirements

• Site condition
Standard rating of Distribution Transformers (11/0.433kV)-
50,63,80,100,160,200,250,315,400,500,630,800,1000,1250,
1600 and 2000kVA
Cooling- Oil Natural Air Natural(ONAN), Oil Natural Air
Forced(ONAF),
Parallel operation of transformers- A pair of transformer is
said to be parallel if they are connected in parallel on at
least two sides for meeting higher loads
Condition for parallel operation
• Same vector group
• Turns ratios should be similar
• Same % impedance voltage
• Ratio of the rated capacities of the transformers shall not
be more than 3:1
Typical single line layout of Transformer Substation and Main Switch
Board(MSB)
Types of Substations

Consider distribution

1.Outdoor Substation
(i) Pole mounted outdoor substation
(ii) Floor mounted outdoor substation

2.Indoor type-Floor mounted

Outdoor Substation
• H-pole structure, base channel of
100mmx50mm size
• Erected at a height of 2.44m from ground level
• 11kV Lightning arrestors(3 numbers) are
erected at the top
• Earth terminals of all 3 LAs are joined together
and connected to earth
• The 11kV gang operated switch( Air Break
switch) installed below the 11kV conductor
taps the 11kV supply to the transformer
• Operating handle located on one pole of the
structure 1.25m from ground
• 11kV horn gap(HG) fuses, installed below the
gang operating switch
• On LT side 3.5 core LT cables are used, LT
cables are selected according to capacity of
transformer
• Connecting jumpers from the 11kV line to the
G O switch, from the G O to HG fuse , and
from the fuse unit to transformer bushing,
covered with empire tape or polythene pipe
for safety
Air Break Switch-AB Switch
HORN GAP FUSE is a protective device used to protect the
equipment from higher voltage, horn gap fuse is a thin wire
element compared to load line when a high current is drawn
from the line, fuse wire melts and protects the equipment
Indoor Substation
▪ 11 kV/415V are frequently used
▪ HT and LT switchgear and cable trench for
incoming and outgoing cables
▪ Adequate clearance between walls and
equipment to ensure safety
▪ Adequate ventilation
▪ The supply from the OH line is brought inside
the substation through UG cable using an
outdoor cable box
▪ The secondary terminal is to be connected to
an LT CB or switch fuse unit using 3.5 core LT
cable
▪ For current upto 300A switch fuse unit are
used
▪ For metering PTs & CTs are installed at HT side
and measure Maximum demand, PF etc
▪ Two separate distinct earth electrode shall be
provided for neutral earthing, body earthing
and lightning arrester earthing.
 Installation of transformer substation
Outdoor type
▪ Minimum clearance between suppliers and
consumers 11kV structure shall be 3m
▪ Phase to phase clearance 915mm and phase to
earth 610mm
▪ Minimum safety clearance of 2.6m between
bare conductor and live parts
▪ Lightning arrestors –between AB(Air Break)
Switch and D.O(drop out) Fuse
▪ AB switch operating handle- 1m to 1.25m from
ground level
▪ 11kV AB switches shall be three insulators types
Indoor Type
Recommended for rating above 630kVA
▪ Only dry type
▪ In case of oil indoor type
▪ free access for fire engines to the transformer
stations
▪ Minimum clearance of 1.5m from building
▪ substation building shall be weatherproof and
fireproof, walls of 355mm thick brick or
230mm thick RCC
▪ AB switch fuse unit/ VCB shall be provided on
the primary side
▪ Minimum size of cable on 11kV side -150 sq.mm
XLPE
▪ Fire separation walls shall be provided in
between oil filled transformers
▪ Oil drainage facility/soak pits shall be insisted for
oil type
▪ All round clearance shall be provided- minimum
1.25m if wall are provided at four sides
▪ Adequate ventilation easy access
▪ Doors and windows of transformer room –non
flammable material
▪ Minimum 50cm headroom clearance
▪ Minimum phase to phase 130mm and phase to
ground 80mm clearance of busbars in 11kV
panel
 Selection of Switchgears
Basic Functions
• Electrical protection( Overload, short circuits,
insulation failure)
• Electrical isolation of a section of the
installation( a gap interposed insulating
barrier between the open contacts)
• Local or remote switching( functional,
emergency switching, emergency stopping,
switching off for maintenance)
Electrical Protection
Protection of circuit elements( against overloading,
provided by fuse or CB)
Protection of persons and livestock( due to
insulation failure, protection through fuses, CBs,
ELCB or RCCB)
Protection of equipment (against overheating , single
phasing, protection through thermal relay)
Electrical isolation- Separate a circuit or equipment
from other installation to carry out work. In the
isolation neutral pole must be opened, provided
with mechanical locking, comply with national
standards, visual indication complete opening of
contacts
Switching control
Functional control-Includes all switching operations
during normal conditions for energizing and de-
energizing of a part of a system or installation or
equipment
Emergency control- It is a built in facility to de-energise a
live circuit which could be dangerous to person and
property. Provide large red mushroom headed
emergency stop button, single action guarantee
complete switching off.
Maintenance operation-To enable maintenance work,
stopping or disconnect a piece of equipment or circuit
 Switching Devices
1.Isolators-Manually operated ON/OFF switch with
provision for locking and provides safe operation.
Cannot operated under loaded condition
2.Load break switch-Design for operation on
loaded circuit, under normal operating condition.
Non-automatic ON/OFF switching device
3.Contactors-It is a solenoid operated switch which
is held closed by a current through a solenoid
coil.
4.Discontactors-A contactor equipped with a
thermal relay for protection against over current
is defined as a discontactors. It is not a CB
5.Changeover switches-Wide application in
situations when the reliability of electrical supply
from utility is low and are used in
lighting/industrial applications wherever continuity
of supply is necessary. ON load as well as OFF load
available
6.Automatic transfer switch (ATS)-Automatic
transfer of power. By using Automatic Main
Failure(AMF) system. It is self acting equipment
containing the transfer switching devices and other
accessories for monitoring the supply sources and
for transferring load circuit from one supply to
another.