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Indus Institute of Engineering &
Technology Kinana, Jind – 126102
ELECTRICAL ENGG. DEPARTMENT
PROJAECT REPORT ON:-
400/220kv SUBSTATION
(INDIAN OIL CORPORATION LIMITED)
SUBMITTED BY:-
SUBMITTED TO:-
ANIL KUMAR
MS.RICHA GOUR
(5608181)
(HEAD OF DEPARTMENT)
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ACKNOWLEDGEMENT:I am extremely thankful & indebted to the numerous IOCL Engineers, who provided vital
information about the functioning of their respective departments thus helping me to gain an
overall idea about the working of organization. I am highly thankful for the support & guidance
of each of them. I am highly indebted to my project guide, Mr.SubhashRakshit, Ms. Aditi
Sharma for giving me his valuable time and helping me to grasp the various concepts of
switchyard equipments and their control instruments and their testing. Last but not the least, I
would like to thank my parents & all my fellow trainees who have been a constant source of
encouragement & inspiration during my studies & have always provided me support in every
walk of life.
We are very grateful to Shri Rajeder Singh. He has introduced us to the control room. He helped
us to gain knowledge about the operation system of various lines, transformer and their applied
equipments for Six weeks
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Contents:
What is an Electrical Substation?

Introduction: about substation

Overview of substation

Single line digram of substation

Brief description

Power transformer

Transmission towers and structures

Isolators

Circuit breaker

Lightning arrestor

Current transformer

Potential transformer

Capacitor voltage transformer

Arching horns

Underground cables

Wave trap

Protective relays

Shunt reactor for bus voltage

Capacitor bank

Clearance at glance

Other definitions

Communication in the substation

Specification and rating
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Electrical Substation :“Electric Power is generated in Power Stations and transmitted to various cities and towns.
During transmissions, there are power (energy) loss and the whole subject of Transmission and
Distribution...
An electrical substation is a subsidiary station of an electricity generation, transmission and
distribution system where voltage is transformed from high to low or the reverse using
transformers. Electric power may flow through several substations between generating plant and
consumer, and may be changed in voltage in several steps.
The word substation comes from the days before the distribution system became a grid. The first
substations were connected to only one power station where the generator was housed, and were
subsidiaries of that power station.
Elements of a substation:Substations generally have switching, protection and control equipment and one or more
transformers. In a large substation, circuit breakers are used to interrupt any short-circuits or
overload currents that may occur on the network.
Smaller distribution stations may use reclosecircuit breakers or fuses for protection of
distribution circuits.
Substations do not usually have generators, although a power plant may have a substation
nearby. Other devices such as powerfactor correction capacitors and voltage regulators may also
be located at a substation.
Substations may be on the surface in fenced enclosures, underground, or located in
specialpurposebuildings.
High-rise buildings may have several indoor substations. Indoor substations are usually found in
urban areas to reduce the noise from the transformers, for reasons of appearance, or to protect
switchgear from extreme climate or pollution conditions.
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Where a substation has a metallic fence, it must be properly grounded (UK: earthed) to protect
people from high voltages that may occur during a fault in the network. Earth faults at a
substationcan cause a ground potential rise.
Currents flowing in the Earth's surface during a fault can causemetal objects to have a
significantly different voltage than the ground under a person's feet; this touch potential presents
a hazard of electrocution.
Transmission substation:A transmission substation connects two or more transmission lines. The simplest case is where
all transmission lines have the same voltage. In such cases, the substation contains high-voltage
switches that allow lines to be connected or isolated for fault clearance or maintenance.
A transmission station may have transformers to convert between two transmission voltages,
voltagecontrol devices such as capacitors, reactors or static VAr compensator and equipment
such as phase shifting transformers to control power flow between two adjacent power systems.
Transmission substations can range from simple to complex. A small "switching station" may be
little more than a bus plus some circuit breakers. The largest transmission substations can cover a
large area (several acres/hectares) with multiple voltage levels, many circuit breakers and a large
amount of protection and control equipment (voltage and current transformers, relays and
SCADA systems).
Distribution substation:
A distribution substation in Scarbor-ough, Ontario, Canada disguised as a house, complete with a
driveway, front walk and a mown lawn and shrubs in the front yard. A warning notice can be
clearly seen on the "front door".
A distribution substation transfers power from the transmission system to the distribution
system of an area. It is uneconomical to directly connect electricity consumers to the highvoltage main transmission network, unless they use large amounts of power, so the distribution
station reduces voltage to a value suitable for local distribution.
The input for a distribution substation is typically at least two transmission or sub transmission
lines. Input voltage may be, for example, 115 kV, or whatever is common in the area.
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Distribution voltages are typically medium voltage, between 2.4 and 33 Kvdepending on the size
of the area served and the practices of the local utility.
Introduction: about substation:400 kvrefinary substation is one important substation of IOCL. It is one of the largest power
grids in the state of HARYANA and the north India. It is situated at National
Highway-1 Panipat. The construction of this substation completed during 1990-95 by
IOC(INDIAN OIL CORPORATION) .The area of this substation is about 500 acre.
The whole substation is divided in four parts:
1. 132kv switchyard
2. 400/220kv switchyard
3. 765kv switchyard
For 400kv &220kv switchyard a common control room is used and for 132kv switchyard
A separate control room used. IOCL, an Indian Multinational with manufacturing bases in 8
countries, have signed the contract on 5th March’2010 with Indian Oil Corporation Ltd for
construction of 765/400 kV Substation at refinery, in Panipat. The value of contract is Rs 302
Corers .
A 765/400 kV substation is the highest grade system voltage for transmission in India. IOCL is
first state utility to enter into 765 kV area.
The scope of the project includes Design, Engineering, Manufacture, Supply, Erection, Testing
and Commissioning of 8 Bays of 765 kV & 2 Bays of 400kV, along with 7 Nos. of 333 MVA
(Single Phase) 765/400 kV Power Transformers and 7 Nos. of 110 MVAR (Single Phase) 765
kV Shunt Reactor & 4 Nos. 63 MVAR (Single Phase) 765 kV Reactors. The project is expected
to be commissioned in July 2011.
The project is of strategic importance for entry into market of 765 kV Substations globally and
widens up the horizon for the entire product range of CGL
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Overview of substation:As we said earlier the whole substation is divided in three parts:132kv site ,400/220kv site and
765 kv site 765 kv sit is on under construction. The civil work is completing by L&T Company.
Other part of project Design, Engineering, Manufacture, Supply, Erection, Testing and
Commissioning of Bays will complete by CGL.
In 400/220kv switchyard following outdoor instrument used:
1. One 400kv transfer bus control bus coupler
2. Two 100MVA 220/132kv autotransformer
3. Two 315MVA 400/220kv autotransformer
4. Five 50MVAR shunt reactor
5. Two 63MVAR bus reactor
6. 15 lighting tower
7. SF6 circuit breaker
8. Capacitor voltage transformer(CVT)
9. Current transformer(CT)
In whole switchyard following main equipment are used:
i) One 400kv transfer bus control bus coupler.
ii) Two 100MVA 220/132 KV auto transformer manufactured from BHEL.
iii) Two 315 MVA 400/220 KV auto transformer manufactured from BHEL.
iv) Five 50 MVAR shunt reactor manufactured from BHEL.
v) Two 63 MVAR bus reactor manufactured from HITACTI.
vi) Circuit breaker from CGL.
vii) Isolators from S&S.
viii) Current transformer from WS and CGL.
ix) CVT
x) Wave trap
xi) Lighting arrester
xii)Surge capacitor
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Single line diagram of Refinary substation:-
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Brief Description Of all Outdoor Equipment:Power transformer:Various types of transformers have been provided at 220& 400 KV Substation from IOCL.
Capacity and voltage ratio wise 100 MVA , 315MVA & 160 MVA and 220/132/11 kV. 400/220
kV, These transformers are of TELK, BHEL, GEC, NGEF, C & G, Hitachi and Bharat Bijlee
make and have most of the features common except few accessories which may be different. In
this substation all transformers made by BHEL. These
transformers have following main components:
1. MAIN CORE & WINDING.
2. BUSHING :(a) 220 kV High voltage bushings:
Condenser type bushings with insulating body and central conducting tubebackelised with paper
wound capacitor have been provided. Innermost of the capacitor layer is electrically connected to
the tube and outermost to the mounting flange on insulating body. The central tube insulating
body and mounting flange are oil filled assembled. High dielectric Strength oil is filled between
central tube and insulating body. Oil level indicators are provided on the bushing.
(b) 132 kV Medium voltage bushing:
These bushing are also of condenser type and are of similar construction as in the
case of 220 kV bushing in 200 MVA transformers. In 40 & 20 MVA transformers 132 kV
bushings are also of oil filled type in which oil is filled up when the transformer tank is topped
up. Necessary air vent screws are provided on top of the bushings for release of trapped air at the
top of oil fitting.
(c) 66 kV. 33 kV. & 11 kV. Bushings:
These are oil filled bushing and simpler in construction.
3. TAP CHANGER:The transformers have been provided with on load tap changer, which consists of diverter switch
installed in an oil compartment separated from transformer oil and the tap selector mounted
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below it. The tap changer is attached to the transformer cover by means of tap changer head,
which also serves for connecting the driving shaft and the oil conservator.
4. PROTECTIVE RELAYS:Generally there are two protective buchholz relays, one for main transformer tank and other for
tap changer. In 40MVA GEC transformers oil surge relay has also been provided in tap changer.
5. PRESSURE RELIEF VALVE:40 MVA GEC make transformers have been provided with pressure relief valve which
operates in case of sudden pressure formation in side the transformer.
6. COOLING SYSTEM :100 MVA transformers have been provided with cooling bank installed on separate
structures. These cooling banks have provided with to groups of fans and 2 nos. pumps.
These fans and pumps automatically operate, depending upon the settings of winding
temperature Indicator.
7. TERTIARY BUSING:100 MVA transformers have been provided with tertiary bushing connected with 11 kv
capacitor and lighting arrestor t absorb switching surges.
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ELECTRICAL PROTECTION :The following electrical protection have been provided on the transformers :(i) Differential Protection
(ii) Restricted Earth Fault
(iii) Winding temp high
(iv) Oil temp high
(v) Pressure relief valve
(vi) Oil surge relay
(vii) Over current relay
(viii) Local Breaker Back up protection
(ix) Surge arrestors on HV, MV & LV sides.
The main Tank - The transformer is transported on trailor to substation site and as far as possible
directly unloaded on the plinth. Transformer tanks up to 25 MVA capacity are generally oil
filled, and those of higher capacity are transported with N2 gas filled in them+ve pressure of N2
is maintained in transformer tank to avoid the ingress of moisture.
This pressure should be maintained during storage; if necessary by filling N2 Bushings generally transported in wooden cases in horizontal position and should be stored in that
position. There being more of Fragile material, care should be taken while handling them.
Rediators –
These should be stored with ends duly blanked with gaskets and end plates to avoid in gross of
moisture, dust, and any foreign materials inside. The care should be taken to protect the fins of
radiators while unloading and storage to avoid further oil leakages.
The radiators should be stored on raised ground keeping the fins intact. Oil Piping. The Oil
piping should also be blanked at the ends with gasket and blanking plates to avoid in gross of
moisture, dust, and foreign All other accessories like temperature meters, oil flow indicators,
PRVs, buchholtz relay; oil surge relays; gasket ‘ O ‘ rings etc. should be properly packed and
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stored indoor in store shed. Oil is received in sealed oil barrels . The oil barrels should be stored
in horizontal position with the lids on either side in horizontal position to maintain oil pressure
on them from inside and subsequently avoiding moisture and water ingress into oil.
The transformers are received on site with loose accessories hence the materials should be
checked as per bills of materials.
The transformers that are used in Refinary substation have following specification:
Specification of 100 MVA 220/132/11 KV 3-Φ auto transformer:Types of cooling ONAN ONAF OFAF
Rating of H.V. & I.V.(MVA) 60 80 100
Rating of L.V. (MVA) 18 24 30
Line current H.V.(Amps) 157.4 209.9 262.4
Line current I.V. (Amps) 262.4 349.9 437.4
Line current L.V. (Amps) 944.8 1259.7 1574.6
No load voltage H.V. 220KV
No load voltage I.V. 132KV
No load voltage L.V. 11KV
Temp. Rise winding ˚C 55 55 60
[ Above ambient of 50 ˚C ]
Temp. rise oil ˚C 50 [ Above ambient of 50 ˚C ]
Phase 3
Frequency 50Hz
Connection symbol YNa0d11
Insulation level:
H. V. - LI950 AC395-AC38
L. V. - LI170 AC70
I. V. - LI550-AC230-AC38
Core & winding (Kg.) 54000
Weight of oil (Kg.) 39410
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Total weight (Kg.) 127995
Oil quantity (liters) 45300
Transport weight (Kg. ) 69000
Untanking weight (Kg.) 54000
Specification of 315 MVA 400/220 KV 3- Φ auto transformer:Types of cooling ONAN ONAF OFAF
Rating of H.V. & I.V.(MVA) 189 252 315
Rating of L.V. (MVA) 105 105 105
Line current H.V.(Amps) 272.76 363.68 454.6
Line current I.V. (Amps) 495.96 661.28 826.6
Line current L.V. (Amps) 837.0 1857.0 1837.0
No load voltage H.V. 400KV
No load voltage I.V. 220KV
No load voltage L.V. 33KV
Temp. Rise winding ˚C 55 55 60
[ Above ambient of 50 ˚C ]
Temp. rise oil ˚C 50 [ Above ambient of 50 ˚C ]
Phase 3
Frequency 50Hz
Connection symbol YNa0d11
Insulation level:
H. V. - LI950 AC395-AC38
L. V. - LI170 AC70
I. V. - LI550-AC230-AC38
Oil quantity (liters) : 84550 liter
Impedance volt
315 MVA Base
H.V. position 9/L.V. 71.81%
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H.V. position 9/I
.V. 11.47%
I.V./L.V. 67.92%
Transmission towers and structures:-
Tower is a lattice structure that supports insulators, overhead transmission line and overhead
earth wires. Towers and structures are three dimensional fabricated lattice structures made up by
bolting, riveting and welding the structural members of galvanized steel. Due to limitation of
transmitting voltage up to 400kV, in India rigid self supporting towers are used for transmission.
The towers may be single or double circuit. When a tower has only one circuit it is called vertical
tower. Double circuit tower is called horizontal tower.
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Depending on several factors towers may be classified as follows:
Straight Line Tangent or Suspension Tower

Section Tower or Tension Tower

Small Angle Tower ( 2 to 15 degree)

Medium Angle Tower ( 15 to 30 degree)

Large Angle Tower ( > 30 degree) with dead end

Large Angle with Corner End

Anchor Tower

Long Span Tower

Transposition Tower

Take-off Tower or Turning Tower

Crossing Tower

Anti-wind Tower
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Isolators:In electrical engineering, a disconnecter or isolator switch is used to make sure that an electrical
circuit can be completely de-energized for service or maintenance. Such switches are often found
in electrical distribution and industrial applications where machinery must have its source of
driving power removed for adjustment or repair. High-voltage isolation switches are used in
electrical substations to allow isolation of apparatus such as circuit breakers and transformers,
and transmission lines, for maintenance.
In the substation following type isolators are used for the protection:
Horizontal break center rotating double break isolator:This type of construction has three insulator stacks per pole. The two one each side is fixed and
one at the center is rotating type. The central insulator stack can swing about its vertical axis
through about 900C. The fixed contacts are provided on the top of each of the insulator stacks on
the side. The contact bar is fixed horizontally on the central insulator stack. In closed position,
the contact shaft connects the two fixed contacts. While opening, the central stack rotates
through 900C, and the contact shaft swings horizontally giving a double break.
The isolators are mounted on a galvanized rolled steel frame. The three poles are interlocked by
means of steel shaft. A common operating mechanism is provided for all the three poles. One
pole of a triple pole isolator is closed position.
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Pantograph isolator:illustrates the construction of a typical pantograph isolator. While closing, the linkages of
pantograph are brought nearer by rotating the insulator column. In closed position the upper two
arms of the pantograph close on the overhead station bus bar giving a grip. The current is carried
by the upper bus bar to the lower bus bar through the conducting arms of the pantograph. While
opening, the rotating insulator column is rotated about its axis. Thereby the pantograph blades
collapse in vertical plane and vertical isolation is obtained between the line terminal and
pantograph upper terminal.
Pantograph isolators cover less floor area. Each pole can be located at a suitable point and the
three poles need not be in one line, can be located in a line at desired angle with the bus axis.
Isolator with earth switches (ES):The instrument current transformer (CT) steps down the current of a circuit to a lower value and
is used in the same types of equipment as a potential transformer. This is done by constructing
the secondary coil consisting of many turns of wire, around the primary coil, which contains only
a few turns of wire. In this manner, measurements of high values of current can be obtained. A
current transformer should always be short-circuited when not connected to an external load.
Because the magnetic circuit of a current transformer is designed for low magnetizing current
when under load, this large increase in magnetizing current will build up a large flux in the
magneticPantograph isolatorcircuit and cause the transformer to act as a step-up transformer,
inducing an excessively high voltage in the secondary when under no load. The main use of
using the earth switch (E/S) is to ground the extra voltage which may be dangerous for any of the
instrument in the substation.
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Circuit breaker:A circuit breaker is an automatically-operated electrical switch designed to protect an electrical
circuit from damage caused by overload or short circuit. Its basic function is to detect a fault
condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a
fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either
manually or automatically) to resume normal operation. Circuit breakers are made in varying
sizes, fromsmall devices that protect an individual household appliance up to large switchgear
designed to protect high voltage circuits feeding an entire city. Once a fault is detected, contacts
within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy
(using something such as springs or compressed air) contained within the breaker is used to
separate the contacts, although some of the energy required may be obtained from the fault
current itself.
Small circuit breakers may be manually operated; larger units have solenoids to trip the
mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts
must carry the load current without excessive heating, and must also withstand the heat of the arc
produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver
alloys, and other materials. When a current is interrupted, an arc is generated. This arc must be
contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can
again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating
gas or oil as the medium in which the arc forms. Different techniques are used to extinguish the
arc including:
Lengthening of the arc
Intensive cooling (in jet chambers)
Division into partial arcs
Zero point quenching (Contacts open at the zero current time crossing of the AC waveform,
effectively breaking no load current at the time of opening. The zero crossing occures at twice
the line frequency i.e. 100 times per second for 50Hz ac and 120 times per second for 60Hz ac )
Connecting capacitors in parallel with contacts in DC circuits
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Finally, once the fault condition has been cleared, the contacts must again be closed to restore
power to the interrupted circuit.
Types of circuit breaker:Many different classifications of circuit breakers can be made, based on their features such as
voltage class, construction type, interrupting type, and structural features.
Electrical power transmission networks are protected and controlled by high-voltage breakers.
The definition of high voltage varies but in power transmission work is usually thought to be
72.5 kV or higher, according to a recent definition by the International Electrotechnical
Commission(IEC).
High-voltage breakers are nearly always solenoid-operated, with current sensing protective
relays operated through current transformers. In substations the protection relay scheme can be
complex, protecting equipment and busses from various types of overload or ground/earth fault.
High-voltage breakers are broadly classified by the medium used to extinguish the arc.
Bulk oil
Minimum oil
Air blast
Vacuum
SF6
In refinary substation only SF6 circuit breaker is used. The breaker uses SF6
(SulpherHexafluoride) gas for arc extinction purpose. This gas has excellent current interrupting
and insulating properties, chemically, it is one of the most stable compound in the pure state and
under normal condition it is physically inert, non-flammable, non toxic and odorless and there is
no danger tepersonnel and fire hazard. It's density is about. 5 times that of air insulating strength
is about 2-3 times that of air and exceeds that of oil at 3 Kg/Cm pressure.
SF6 breaker called as maintenance free breaker, has simple construction with few moving parts:
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The fission products created during breaking and not fully recombined are, either precipitated as
metallic fluoride or absorbed by a static filter which also absorbs the residual moisture. Since no
gas is exhausted from the breaker and very little compressed air is required for operation, noise
during the operation is also very Jess.
Since SF6 gas is inert and stable at normal temperature, contacts do not settler from oxidization
or other chemical reactions, whereas in air or oil type breakers oxidation of contacts would
causehigh temperature rise.
SF6 gas circuit breakers, designed to conform to the same standards as airor oil breakers, but in
operation it is possible to get better service even at higher fault levels.
Sulphur hexafluoride gas is prepared by burning coarsely crushed roll sulphur in the fluorine gas,
in a steel box, provided with staggered horizontal shelves, each bearing about 4 kg of sulphur.
The steel box is made gas tight. The gas thus obtained contains other fluorides such as S2F10,
SF4 and must be purified further SF6 gas generally supplier by chemical firms. The cost of gas is
low if manufactured in large scale.
During the arcing period SF6 gas is blown axially along the arc. The gas removes the heat from
the arc by axial convection and radial dissipation. As a result, the arc diameter reduces during the
decreasing mode of the current wave. The diameter becomes small during the current zero and
the arc is extinguished. Due to its electro negativity, and low arc time constant, the SF6 gas
regains its dielectric strength rapidly after the current zero, the rate of rise of dielectric strength is
very high and the time constant is very small.
Fig: SF6 circuit breaker.
Gas circuit breaker: high voltage side
Type 220-SFM-20B
Voltage rating: 220kv
Rated lightening impulse withstand voltage: 1050 kVp
Rated short circuit breaker current: 40 kV
Rated operating pressure: 16.5 kg/ cm2g
First pole to clear factor 1.3
Rated duration of short circuit current is 40 kA for 30 sec.
Rated ling charging breaker breaking current 125 Amp
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Rated voltage 245 kV
Rated frequency 50 Hz
Rated normal current 1600 Amp
Rated closing voltage: 220 V dc
Rated opening voltage 220 V dc
Main parts:
(a) Power circuit
(b) Control circuit
Gas circuit breaker: low voltage side
Type 120-SFM-32A
Voltage rating: 220kv
Rated lightening impulse withstand voltage: 650 kVp
Rated short circuit breaker current: 31.5 kV
Rated operating pressure: 15.5 kg/ cm2g
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Lightning arrester:High Voltage Power System experiences overvoltages that arise due to natural lightning or the
inevitable switching operations. Under these overvoltage conditions, the insulation of the power
system equipment are subjected to electrical stress which may lead to catastrophic failure.
Broadly, three types of overvoltages occur in power systems:
(i)temporary over-voltages,
(ii)switching overvoltages and
(iii) lightning overvoltages.
The duration of these overvoltages vary in the ranges of microseconds to sec depending upon the
type and nature of overvoltages. Hence, the power system calls for overvoltage protective
devices to ensure the reliability.
Conventionally, the overvoltage protection is obtained by the use of lightning / surge arresters .
Under normal operating voltages, the impedance of lightning arrester, placed in parallel to the
equipment to be protected, is very high and allow the equipment to perform its respective
function. Whenever the overvoltage appears across the terminals, the impedance of
thearrestercollapses in such a way that the power system equipment would not experience the
overvoltage. As soon as the overvoltage disappears, the arrester recovers its impedance back.
Thus the arrester protects the equipment from overvoltages.
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The technology of lightning arresters has undergone major transitions during this century. In the
early part of the century, spark gaps were used to suppress these overvoltages. The silicon
carbide gapped arresters replaced the spark gaps in 1930 and reigned supreme till 1970. During
the mid 1970s, zinc oxide (ZnO) gapless arresters, possessing superior protection characteristics,
replaced the silicon carbide gapped arresters. Usage of ZnO arresters have increased the
reliability of power systems many fold.
Current transformer:Current Transformers (CT’s) are instrument transformers that are used to supply a reduced value
of current to meters, protective relays, and other instruments. CT’s provide isolation from the
high voltage primary, permit grounding of the secondary for safety, and step-down the
magnitude of the measured current to a value that can be
safely handled by the instruments.
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TECHNICAL SPECIFICATION FOR
CURRENT TRANSFORMERS:1.0 GENERAL:1.1 This specification covers manufacture, test, & supply of LT Current transformers of
class 0.5 accuracy.
1.2 The CTs shall be suitable for metering purpose.
2.0 TYPE:2.1 The CTs shall be of ring type or window type (bar type or bus-bar type CT’s shall not be
accepted).
2.2 The secondary leads shall be terminated with Tinned Cooper rose contact terminals with
arrangements for sealing purposes.
2.3 Polarity (both for primary and second leads) shall be marked.
2.4 The CTs shall be varnished, fiberglass tape insulated or cast resin, air-cooled type. Only
super enameled electrolytic grade copper wires shall be used.
2.5 The CTs shall conform to IS 2705:Part-I & II/IEC:185 with latest amendments.
TECHNICAL DETAILS:3.1 Technical details shall be as given below:
1. Class of Accuracy 0.5
2. Rated Burden 5.00 VA
3. Power Frequency Withstand Voltage 3KV
4. Highest System Voltage 433 V
5. Nominal System Voltage 400 V
6. Frequency 50 Hz
7. Supply System 3 Ph. Solidly grounded Neutral System
3.2 Transformation ratio shall be specified from the following standard ratings as per
requirement :
Ratio 50/5 150/5 300/5 400/5 1000/5
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(Secondary with 1 A may be specified by the utility incase the same is desired.)
3.3 Bore diameter of the CT shall not be less than 40 mm. Ring type CTs shall have suitable
clamp to fix the CT to panel Board, wherever required.
3.4 The limits of current error and phase angle displacement as per IS:2705 at several defined
percentage of rated current are:
Accuracy
Class
% Ratio error at % of rated current
Phase displacement in minutes at % of rated current
5 20 100 120 5 20 100 120
0.5 1.5 0.75 0.5 0.5 90 45 30 30
Note : Current error and phase displacement at rated frequency is required to be as above when
the secondary burden from 25% to 100% of the rated burden i.e. 50 V A.
3.5 Rated extended primary current shall be 120% of rated primary Current in accordance with
IS:2705 Pt-II.
3.6 Rated ISF (Instrument Security Factor) shall be declared by the manufacturer & marked on
the CT.
3.7CT’s shall be made with good engineering practices. Core winding shall evenly spread stress
&avoid stress concentration at any one point. Cast resin CT’s shall be processed by hot curing
method under controlled vacuum conditions.
3.8 The base shall be of hot dip galvanized steel.
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4.0 TESTS:4.1. TYPE TESTS:4.1.1 Copies of all type tests as per IS.2705 Part-I and II including short time current &
temperature rise tests in NABL accredited laboratory shall be submitted and got approved before
commencement of supply.
4.2 ROUTINE TESTS:
4.2.1 The supplier shall conduct all the routine tests such as Ratio test, phase angle error test for
0.5 accuracy class as per IS 2705 Part I & II.
4.3 Commissioning test :
4.3.1 In accordance with IS:2705, Power frequency test on primary winding shall be carried out
after erection on site on sample basis.
5.0 Marking :5.1 The CTs shall have marking and nameplate as per IS 2705 in addition to class of insulation
&ISF. The markings shall be indellible. The nameplate shall be securely fixed to the body of the
CT.
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Potential transformer:It is essentially a step down transformer that steps down the voltage to a known value. The
primary of this transformer consists of a large number of fine wires connected across the line.
The secondary winding consists of a few turns that provides for measuring instruments and
relays, a voltage which is a known fraction of the line voltage.
The potential transformers are classified as;
1.Magnetic type (up to 132 kV)
2.Capacitive type (CVT) (above 132 kV)
PTs are important in case of voltmeter, wattmeter, distance, and directional relays. Its one end of
the primary winding is grounded so it has only input bushing and it is connected in parallel with
the bus. In Kasba substation, the CVT is also used as the coupling capacitor for power line
carrier communication, for protecting the low frequency noise.
28
Capacitor voltage transformer:In high and extra high voltage transmission systems, capacitor voltage transformers (CVTs) are
used to provide potential outputs to metering instruments and protective relays. In addition, when
equipped with carrier accessories, CVTs can be used for power line carrier (PLC) coupling.
A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down
extra high voltage signals and provide low voltage signals either for measurement or to operate
aprotective relay.
In its most basic form the device consists of three parts: two capacitors acrosswhich the voltage
signal is split, an inductive element used to tune the device to the supply
frequency and a transformer used to isolate and further step-down the voltage for the
instrumentation or protective relay. The device has at least four terminals, a high-voltage
terminal for connection to the high voltage signal, a ground terminal and at least one set of
secondary terminals for connection to the instrumentation or protective relay. CVTs are typically
single-phase devices used for measuring voltages in excess of one hundred kilovolts where the
use of voltage transformers would be uneconomical. In practice the first capacitor, C1, is often
replaced by a stack of capacitors connected in series. This results in a large voltage drop across
the stack of capacitors that replaced the first capacitor and a comparatively small voltage drop
across the second capacitor, C2, and hence the secondary terminals.
29
Arcing horns:-
Arcing horns (arc horns) are projecting conductors used to protect insulators on high voltage
electric power transmission systems from damage during flashover. The horns encourage flash
over between themselves rather than across the surface of the insulator they serve to protect.
Horns are normally paired on either side of the transformer, one connected to the high voltage
part and other to ground. They are frequently seen on insulator strings, or protecting transformer
bushings. The horns can take various forms such as simple cylindrical rods, circular guard rings
or contoured curves, sometimes known as stirrups.
High voltage equipment particularly that which is installed outside such a overhead power line is
commonly subjected to transient overvoltage, which may be caused by phenomena such as
lightning strikes, faults on other equipments or switching surges during circuit re-energisation.
Over voltage conditions such as these are un-predictable and in general cannot be prevented.
Line terminations at which a transmission line connects to a bus bar or a transformer bushing, are
at greatest risk to over voltage due to change in characteristic impedance at this point.
An electrical insulator serves to provide physical separation of conducting parts and under
normal operating conditions is continuously subject to high electric field which occupies the air
surrounding the equipment. Over voltage event may cause the dielectric field to exceed the
30
dielectric strength of air and result in the formation of an arc between the conducting parts and
over the surface of the insulator. This is called flashover. Contamination of the surface of the
insulator reduces the breakdown strength and increases the tendency to flashover. On an
electrical transmission system protective relays are expected, to detect the formation of the arc
and automatically open the circuit breakers to discharge the circuit and extinguish the arc. Under
a worst case this process may take several seconds. During which time the insulator surface
would be in close contact with the highly energetic plasma of the arc. This is very damaging to
an insulator and may shatter brittle glass or ceramic discs, resulting in its complete failure.
Arcing horns form a spark gap across the insulators with a lower breakdown voltage than the air
path along the insulator surface. So an over voltage will cause the air to breakdown and the arc to
be formed between the arcing horns diverting it away from the surface of the insulators. An arc
between the horns is more tolerable for the equipment, providing more time for the fault to be
detected and the arc to be safely cleared by the remote circuit breakers. The geometry of some
designs encourages the arc to migrate away from the insulator, driven by rising currents as it
heats up the surrounding air. As it does so the path length increases, cooling the arc, reducing the
electric field and causing the arc to extinguish itself when it can no longer span the gap. Other
designs can utilize the magnetic fields produced by the high current to drive the arc away from
the insulator. This type of arrangement is known as magnetic blowout.
Design criteria and maintenance regimes may treat arcing horns as sacrificial equipment, cheaper
and more easily replaced than the insulator, failure of which can result in complete destruction of
the equipment it insulates. Failure of the insulator strings on overhead lines could result in
parting of the line, with significant safety and cost implications. Arcing horns thus play an
important role in the process of correlating system protection with protective device
characteristics, known as insulation coordination. The horns should provide among other
characteristics, near infinite impedance during normal operating conditions to minimize
conductive current losses, low impedance during the flashover, and physical resilience to the
high temperature of the arc.
As operating voltages increase, greater considerations must be given to such design principles.
At medium voltages, one of the two horns can be omitted as the horn to horn gap can otherwise
be small enough to be bridged by an alighting bird. Alternatively duplex gaps consisting of two
sections on opposite sides on the opposite sides of the insulator can be fitted. Low voltage
31
distribution systems, in which risk of arcing is much lower, may not use arcing horns at all. The
presence of arcing horn necessarily disturbs the normal electric field distribution across the
insulator due to their small but significant capacitance. Most importantly a flashover across an
arcing horn produces an earth fault resulting in circuit outage until the fault is cleared by circuit
breaker operation. For this reason, non linear resistors known as surge diverters can replace
arcing horns at critical locations.
32
Underground cables:-
An underground cable consists of one or more conductors covered with suitable insulation and
surrounded by a protective cover. In practice underground cables are required to deliver three
phase power. But mainly cables are used in a substation to connect the high voltage equipments
in the yard to the control room for controlling and monitoring purpose. For the purpose single
core, 2 cores, 3 core cables are used. But sometimes 4, 8, 12, or 16 core cables are also used.
The various parts of a 3 conductor cable are:
1.
Core or conductors
2.
Insulation
3.
Metallic sheath
4.
Bedding
5.
Armoring
6.
Serving
Insulation is applied over the conductors. The various types of insulation are classified as:
33
i.
Tapped insulation ( impregnated paper or varnished cambric )
ii.
Rubber compound insulation and rubber compound sheaths
iii.
Plastic insulation (polyethylene, PVC, XPLE).
INSULATING SYSTEMS:The external insulation is provided by the porcelain housing and coordinated with the capacitor
stack, consisting of virtually identical elements so that the axial voltage distribution from the line
terminal to ground is essentially uniform. The capacitor elements have a mixed dielectric
material consisting of alternating layers of polypropylene film and Kraft paper. The Kraft paper
layers serve as a wicking agent to ensure homogenous synthetic oil impregnation. The
electromagnetic unit (EMU) is housed in an oil-filled tank at the base of the capacitor stack.
Mineral oil is employed as
the insulating medium instead of air because of its superior insulating and heat transfer
properties.
The use of an oil-filled base tank removes the need for space heaters in the secondary terminal
box as this area is warmed by heat transfer from the insulating oil. This results in a more reliable
and cost effective design.
INSULATING OIL:We use insulating oils with excellent dielectric strength, aging, and gas absorbing properties. The
synthetic oil used for the capacitor units possesses superior gas absorption properties resulting in
exceptionally low partial discharge with high inception/extinction voltage ratings. The oil used
forthe EMU is premium naphthenicmineral oil. The oil is filtered, vacuum dried and degassed
withinhouse processing. It contains no PCB.
34
CAPACITOR STACK:The capacitor stack is a voltage divider which provides a reduced voltage at the intermediate
voltage bushing for a given voltage applied at the primary terminal. The capacitor stack is a
multicapacitor- unit assembly. Each unit is housed in an individual insulator. A cast aluminum
cover is on top of the upper capacitor assembly and is fitted with an aluminum terminal. An
adapter for mounting a line trap on top of the CVT can be
provided with an optional (and removable) HV terminal.
Construction:1. Main coil:The main coil winding are encapsulated by winding continuous filament fiberglass
That has been impregnated with a specially selected epoxy resin harden system. The epoxy resin
fiberglass composite is then curved according to a programmed temperature Schedule.
2. Tuning pack:
Tuning pack is connected in parallel with the main coil to provide a high impedance to the
desired carrier frequency.
3. Lighting arresters:
The line traps are protected by a lighting arrestors against high voltage surges caused by
atmospheric effects or switching operations.
35
Protective relays:-
Protective relaying is one of the several features of power system design. Every part of the power
system is protected. The protective relaying is used to give an alarm or to
cause prompt removal of any element of power system from service when hat element behave
abnormally.
The relays are compact and self-contained devices which can sense abnormal conditions.
Whenever abnormal condition occur , the relays contacts get closed. This in turn closes the trip
circuit of a circuit breaker.
For switchyard protections following type relays are used:
1. Overcurrent relay
2. Earth fault relay
3. REF relay
4. Differential relay
5. Directional relay
6. Over flux relay
7. Buchoolz relay
8. IDMT relay
36
Shunt reactor for bus voltage:In EHV substations, it is a common practice to use breaker switched bus reactors to maintain the
bus voltage within permissible limits under varying load conditions. With the development of
Controlled Shunt Reactor (CSR) which is a thyristor controlled high impedance transformer, a
stable bus voltage can be maintained by providing variable reactive power based on the bus
voltage deviations due to the load variations. The high impedance transformer which is also
known as reactor transformer (RT) can be made to any size without any limitation unlike gapped
core shunt reactors. As a single CSR of large capacity can be realized with suitable control
mechanism, this approach proves to be technically superior and economical compared to the
existing practice of breaker switched bus reactors.
A CSR with a detailed control system is modeled along with a typical EHV system in
PSCAD/EMTDC environment. The study includes the effectiveness of filters introduced in the
tertiary of the reactor transformer in controlling the harmonics generated during partial
conduction of thyristors. The transient and steady state performance of the CSR system for
varying system conditions is studied and the same is compared with the conventional practice.
The paper presents and discusses the results of the study.
Keywords: High impedance transformer, shunt reactor, reactive power, compensation, EHV
systems, voltage control, thyristors. Shunt reactors which are meant to be used for controlling the
bus voltage of sub station are known as bus reactors. These are always connected through a
circuit breaker and switched on or off, based on the voltage variations. In large switching
substations, it is not uncommon to find multiple bus reactors when the total reactor
capacityrequired is large.
Due to limited standard ratings of gapped core shunt reactors, it is necessary to
provide in multiples of standard ratings along with associated bay equipment and space for
accommodating the same. The CSR mentioned above is based on a high impedance transformer
known as Reactor Transformer (RT) with a provision to control from the secondary side through
37
thyristor valves. As RT of any large capacity can be realized as a single three phase unit or three
single phase units, it is possible to provide variable reactive power support by controlling the
firing angle of the thyristor valves. This continuously variable CSR as bus reactor offers
following advantages.
1. Continuously variable reactive power based on the voltage variation.
2. Fast Response to dynamic conditions like load throw off
3. Reduced losses with optimized reactive power support.
4. Better economy in terms of substation space and auxiliary equipment.
Figure: shunt reactor
38
Shunt capacitor bank:-
Shunt capacitor banks are used to improve the quality of the electrical supply and the efficient
operation of the power system. Studies show that a flat voltage profile on the system can
significantly reduce line losses. Shunt capacitor banks are relatively
inexpensive and can be easily installed anywhere on the network. Shunt capacitor banks (SCB)
are mainly installed to provide capacitive reactive compensation/
Power factor correction. The use of SCBs has increased because they are relatively inexpensive,
easy and quick to install and can be deployed virtually anywhere in the network. Its installation
has other beneficial effects on the system such as: improvement of the voltage at the load, better
voltage regulation (if they were adequately designed), reduction of losses and reduction or
postponement of investments in transmission.
39
Other definitions and terms:-
OLTC in a transformer:Onload Tap Changer (OLTC) is used with higher capacity transformers where HT side voltage
variation is frequent and a nearly constant LT is required. OLTC is fitted with
the transformer itself. Multiple tappings from HV windings are brought to the OLTC chamber
and
conacted to fixed contacts. Moving contacts rotates with the help of rotating
mechanism having a spindle. This spindle can be rotated manually as well as electrically with a
motor. Motor is connected in such a way that it can rotate in both the directions so as to rotate
the
OLTC contacts in clockwise and anticlock-wise direction. Two push buttons are fitted on the
LCP
(local control panel) to rotate the motor and hence the OLTC contacts in clockwise and
anticlockwise
direction. This movement of contacts thus controls the
output LV voltage of the transformer. So rotating of OLTC contacts with spindle or push buttons
in
this way is a manuall process. In case this process of rotating the OLTC
contacts and hence controlling the LV side voltage is to be done automatically then a RTCC
(Remote Tap Changer Controller) is installed with the transformer HT Panel. The RTCC sends
signals to LCP and LCP in turn rotates the motor as per the signals received from the the RTCC.
40
Interposing CT:Transformer differential relays compare the phase and magnitude of the current entering one
winding of the transformer with that leaving via the other winding(s). Any difference in Phase or
magnitude between the measured quantities will cause current to flow through the operate
winding of the relay. If this current exceeds the relay setting, tripping of theTransformer circuit
breakers will be initiated. To enable a comparison to be made, the differential scheme should be
arranged so that the relay will see rated current when the full load current flows in the protected
circuit. In order to achieve this, the line current transformers must be matched to the normal full
load current of the transformer. Where this is not the case it is necessary to use an auxiliary
interposing current transformer to Provide amplitude correction. The connection of the line CTs
should compensate for any phase shift arising across the transformer. Alternatively the necessary
phase correction may also be provided by the use of an interposing CT.
41
Local backup protection:-
The primary objective of back-up protection is to open all sources of generation to an
Unclearedfault on the system. To accomplish this objective, an adequate back-up protective
system must meet the following functional requirements:
1. It must recognize the existence of all faults which occur within its prescribed zone
of protection.
2. It must detect the failure of the primary protection to clear any fault as planned.
3. In clearing the fault from the system, it must
a. Initiate the tripping of the minimum number of circuit breakers.
b. Operate fast enough (consistent with coordination requirements) to maintain system stability,
prevent excessive equipment damage, and maintain a prescribed degree of service continuity.
Insulators:Table for insulators string:
Line voltage Single
suspension
Single tension Double
suspension
Double tension
42
Corona ring:-
A corona ring, also called anti-corona ring, is a toroid of (typically) conductive material
located in the vicinity of a terminal of a high voltage device. It is electrically insulated. Stacks of
more spaced rings are often used. The role of the corona ring is to distribute the electric field
gradient and lower its maximum values below the corona threshold, preventing the corona
discharge.
Corona rings are typically installed on very high voltage power line insulators. Manufacturers
suggest a corona ring on the line end of the insulator for above 230 kV and on both ends for
above 500 kV. Corona rings prolong lifetime of insulator surfaces by suppressing the effects of
corona discharge.
43
COMMUNICATION IN THE SUBSTATION:-
Communication is a vital part of any substation. It is necessary to connect HQ, CLD and
different tie line substations. For load dispatching and better power management, communication
is essential.
The KASBA substation employs the following medium for communication are used:
Power line carrier communication using WAVE TRAPPER:
Power line carrier communication means that communication signals are sent through power line
along with the power. The supply to communication system is 48V DC. A PLCC system should
have the following parts:
A telephone exchange system
Battery system with battery charger
A carrier signal generating system
Coupling capacitor
Wave trapper
Earthing switch
Lightning arrestor
Drainage coil
The wave trapper is a tuned LC circuit, where the frequency carrier gets blocked and the power
frequency electrical signal passes into the electrical circuit. High frequency wave passes through
the coupling capacitor but low frequency is blocked here. Drainage coil is used to bypass the
over current surges whereas lightning arrestor is kept here additionally to provide safety against
over voltages and lightning surges. Generally PLCC is done using R phase. The conductor from
the lower end of the coupling capacitor enters the drainage coil. LA and earthing switch enter
into a box, known as Line Matching Unit (LMU). From there a coaxial cable enters to carrier set.
44
Phase modulation is employed in the carrier set circuit. The signal is sent to the transmitter and
after amplification it is passed to the filter.
In kasba substation the receiving end and sending end frequencies are as follows.
KASBA
T.F = 380KHZ
R.F = 428KHZ
Satellite communication:VSAT or Very Small Aperture Terminal communication through satellite is also done in
KASBA substation. It is done with other primary grid substation, CLD, HQ authorities. Due to
weak, noisy, slow and poor receiving qualities this type of communication is not used now days.
VHF radio communication:
This type of communication takes place between 132KV and 33KV substations. The frequency
of sending and receiving signals is 167.125MHz. Its main disadvantage is that it is one way
communication at a time.
P & T phone and mobile communication:
45
There are two P&T phones in Kasba substation. One is used for normal official works and the
other phone line is an emergency line and can be used for CLD or HQ for collecting data from
any feeder or bay. Mobile phones are personal and are used only in emergency.
46
SPECIFICATION AND RATING:POWER TRANSFORMERS: There are three auto transformers for stepping down the
voltage at a level of 220 kV/132 kV/33kV. Two of them are MITSUBISHI Corp., Japan made
and the other is CROMPTON GREAVES India made. Their load capacities are 150MVA and
160 MVA respectively. Their tertiary winding voltage is 33kV. The tertiary voltage of the
CROMPTON GREAVES transformer has been further stepped down to .4kV by an auxiliary
transformer to provide power to the central load of the substation only.
TRANSFORMER 1 and 2 with load tap changer
MAKER’S NAME
MITSUBISHI CORP, JAPAN
MVA RATING
150
VOLTS AT NO LOAD
HV- 220 KV
IV- 132 KV
LV- 33 KV
PHASES
3
SERIAL NO.
7430010302
47
TRANSFORMER 3 with load tap changer:MAKER’S NAME
CROMPTON GREAVES, INDIA
MVA RATING
160
VOLTS AT NO LOAD
HV- 220 KV
IV- 132 KV
LV- 33 KV
AMPERES
HV- 429.9 A
IV- 699.8A
LV- 787.9 A
PHASES
3
SERIAL NO.
7430010302
YEAR OF MANUFACTURING
1995
TEMPERATURE RISE IN OIL AND WINDING
45 DEGREE AND 60 DEGREE
TYPES OF COOLING
ONAN, ONAF, OFAF
CONNECTION SYMBOL:
YNAOD11
48
CIRCUIT BREAKER SPECIFICATIONS KASBA SF6 C.B.:MAKER’S NAME
CROMPTON GREAVES, JAPAN
RATED VOLTAGE
145 KV
RATED NORMAL CURRENT
1600 A
RATED SHORT CIRCUIT CURRENT
31.5 KA
RATED SF6 GAS PRESSURE
6KG/SQ CM AT 20 DEGREE
RATED CLOSING TIME
<130 MS
RATED OPENING TIME
<30 MS
RATED FREQUENCY
50 HZ
GAS WEIGHT
7.5 KG
TOTAL WEIGHT
1450 KG
TYPE
120 SFM- 32B(3 POLE)
RATED MAKING CAPACITY
80 KAP
RATED SHORT TIME CURRENT
31.5 KA FOR 3 SEC
FIRST POLE TO CLEAR FACTOR
1.5
AUXILIARY CIRCUIT VOLTAGE
1 PH, 230 V AC, 50 HZ
49
SPECIFICATIONS OF CTs:CTs are of two types:
Dead Tank type- Here CT tanks are situated well below the instrument. They have their major
insulation over high current carrying primary.
Live Tank type- Here Ct tanks are on the top of the instrument bushings. Primary winding is
short and rigid, therefore more reliable and can withstand high short circuit current. They don’t
have their major insulation over high current carrying primary, so the heat generated can easily
be dissipated, thus having a longer life.
TYPE
IMB 145- SINGLE PHASE
HIGHEST SYSTEM VOLTAGE
145 KV
RATED PRIMARY NORMAL CURRENT
650A
RATED INSULATION LEVEL
145/275/650 KV
DYNAMIC CURRENT(KA PEAK)
80.3
CLASS OF INSULATION
A
TOTAL CREEPAGE
3725
RATED SHORT TIME CURRENT
81.5 KA FOR 3 SEC
50
THANK
YOU
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