power grid corporation of india 400 220 kv vocational training report

8/14/2019 Power Grid Corporation of India 400 220 Kv Vocational Training Report

1/25

CONTENTS

1- ACKNOWLEDGEMENT2- INTRODUCTION3- SWITCHYARD DESIGN

a) ONE & HALF BREAKER ARRANGEMENTb) DOUBLE MAIN & TRANSFER ARRANGEMENT

4- SWITCHYARD COMPONENTSa) BAY

b) ISOLATORc) WAVE TRAPd) CTe) CVT

f) REACTORg) ICTh) CIRCUIT BREAKER

5- SF6 CIRCUIT BREAKER6- SERVICING OF SF6 C.B7- REFERENCES


2/25

POWER GRID CORPORATION OF INDIA

LIMITED

400/220 KV SUB-STAIONKARTARPUR, JALANDHAR(PUNJAB)


3/25

ACKNOWLEDGEMENT

I am very grateful to the working staff members of PGCIL Kartarpur 400/220 KV

sub-station for providing me valuable insights into the working of substation . I am

also very thankful to the Director HR Department PGCIL, North Division, Jammu forgiving me a chance to undergo vocational training with PGCIL.

I am also very thankful to my parents for their affectionate support.


4/25

INTRODUCTION

Power Grid Corporation of India Limited(POWERGRID), is an Indian state-

ownedelectric utilities company headquartered in Gurgaon, India. Power Grid wheels

about 50% of the total power generated in India on its transmission network. Power

Grid has a pan-India presence with around 95,329 Circuit-km of Transmission

network and 156 EHVAC & HVDC sub-stations with a total transformation capacity

of 138,673 MVA. The Inter-regional capacity is enhanced to 28,000 MW. Power Grid

has also diversified into Telecom business and established a telecom network of more

than 25,000 km across the country. Power Grid has consistently maintained the

transmission system availability over 99.00% which is at par with the International

Utilities.

In 1980 the Rajadhyaksha Committee on Power Sector Reforms submitted its report

to the Government of India suggesting extensive reforms in the Indian power sector.

Based on the recommendations of the Rajadhyaksha Committee, in 1981 the

Government of India took the policy decision to form a national power grid which

would pave the way for the integrated operation of the central and regional

transmission systems. Pursuant to this decision to form a national power grid,

PowerGrid was incorporated on October 23, 1989 under the companies Act, 1956 as

the National Power Transmission Corporation Limited, with the responsibility of

planning, executing, owning, operating and maintaining the high voltage transmission

systems in the country. The Company received a certificate for commencement of

business on November 8, 1990. Subsequently, the name of the Company was changed

to Power Grid Corporation of India Limited with effect from October 23, 1992.

POWERGRID has enhanced the inter-regional capacity of National Grid to 28,000

MW. India is divided into 5 Regions - Northern Region (NR), Eastern Region (ER),

Western Region (WR), Southern Region (SR), and North-East Region (NER). Out of

all these Regions the NR, ER, WR, and NER are synchronized which is known as

NEW Grid. Whereas SR is not synchronized with the rest of the regions with AC lines

and hence could run on a slightly different frequency. SR is connected with WR and

ER with HVDC links only. When PGCIL was formed then the responsibility

of Regional Load Despatch Centres (RLDCs) was handed over to POWERGRID by

Central Electricity Authority (CEA). On 25th February, 2009 theNational Load

Despatch Center (NLDC) was inaugurated. Now these Regional Load Despatch

Centres (RLDCs) and National Load Despatch Center (NLDC) form a separate

Organisation namedPOSOCO (Power system Operation Corporation),a wholly

owned subsidiary of POWERGRID.
http://en.wikipedia.org/wiki/Electric_utilitieshttp://www.nldc.in/http://www.nldc.in/http://en.wikipedia.org/wiki/Power_System_Operation_Corporation_Limitedhttp://en.wikipedia.org/wiki/Power_System_Operation_Corporation_Limitedhttp://www.nldc.in/http://www.nldc.in/http://en.wikipedia.org/wiki/Electric_utilities


5/25

SWITCHYARD DESIGN

Any transmission line originates or terminates at a Bus-bar. One bus bar is usually

connected to more than one transmission lines depending upon its power handlingability. Different types of bus-bar designs are used based on requirement. Some of the

commonly used bus bar arrangements are One and a half breaker arrangement,

Double Main & Transfer Arrangement, ring main Arrangement, Mesh Arrangement

and Single Bus Bar Arrangement (with or without Bus sectionalization).

The choice of the type of bus bar arrangement depends on-

1- System voltage.2- Provision of extension with load growth.3- Economy keeping in views the needs and continuity of supply.4- Maintenance possibility with interruption of supply.5- Protection during faults.

In the 400/220 kV switchyard of Power Grid Kartarpur, One and a half Breaker

Arrangement is used for 400 kV transmission line and Double Main & Transfer

Arrangement is used for 220 kV Transmission line. Both types of bus bar

arrangements are explained below.

One and a Half Breaker Arrangement

This type of arrangement needs three circuit breakers for two circuits. The number of

circuit breaker per circuit comes out to be 1, hence the name. This circuit is preferred

in those stations where power handled is large.

FIGURE 1ONE AND HALF BREAKER ARRANGEMENT

C.B

C.B

C.B

C.B

C.B

C.B

C.B

C.B

C.B

BUS-1

BUS-1

CIRCUIT 1 CIRCUIT 1 CIRCUIT 1

CIRCUIT 2 CIRCUIT 2 CIRCUIT 2


6/25

It is clear that three circuit breakers are used in one dia between the two busbars, Bus

1 and Bus 2 for two circuits emerging out of it. Two such dia are shown in the figure.

Following advantages are associated with this type of bus bar arrangement

1- The supply is not interrupted in the event of fault on a bus as either of the bus

can be used to maintain supply and keep the feeders (or transmission lines)charged.

2- The supply is not interrupted in the event of any fault on a circuit breaker.3- Possibility of addition of circuits is always there.

Double Main and Transfer

This arrangement is quite frequently used where load and continuity of supply

justifies additional cost. Generally, this system has two main bus-bars and one transfer

bus-bar. However at Gwalior sub-station, two transfer busbars have been used for

saving area. Both transfer bus-bars are electrically connected to each other. Two bus

bars are used to increase redundancy.

The two main bus-bars are electrically connected to each other through a bus coupler.

They can be connected or disconnected from each other at will, depending upon the

system requirements and contingencies. Under normal conditions both the bus-bars

remain charged. Two bus-bars are used to increase redundancy. This scheme provides

for one transfer bus. To save area and to accommodate more feeders, two transfer bus-

bars can be used but they are electrically connected and treated as one for all

purposes. Such an arrangement is present in the switchyard of the Power Grid

Gwaliors substation. A single line diagram for the Double main and transfer

arrangement is shown below

FIGURE 2DOUBLE MAIN & TRANSFER ARRANGEMENT

C.B

C.BC.B C.B

BUS 1

BUS 2

TRANSFER BUS

FEEDERS


7/25

As shown in the figure, each feeder comes with only one circuit breaker, unlike the

One and a half arrangement where effectively each feeder had two circuit breakers. In

case a fault occurs on the breaker associated with a feeder, the continuity of the

supply could still be maintained by transferring the feeder to the transfer bus. For this,

firstly the transfer bus is charged by closing the TBS or the Transfer Bus Coupler and

then closing the isolator connecting transfer bus and the feeder. One transfer bus isused for all the feeders. However, only one feeder at a time can be put on the transfer

bus. The designing does not permit more than one feeder to be put on the bus at a

time.

Choice of BusBar Scheme

As already explained above, the choice of busbar scheme depends on various

factors like system voltage, protection, redundancy and economy. At the Kartarpur

substation, the 400 kV line are connected to the one and a half breaker bus barwhile the 220 kV line are connected to the double main and transfer busbar.

One and a half breaker arrangement is more reliable as each circuit feeder has

effectively two circuit breakers. In can one has some fault or has to be taken into

maintenance, the arrangement would remain equally effective and power handling

capability would remain same. One breaker with each dia can be safely taken out of

service. However the cost is very high as more circuit breakers are being used. This is

the cost of increased protection and ability to maintain the continuity of supply under

faulty conditions. The cost of a 400 kV line tripping and ultimately going out is very

high as one such line normally handles 500600 MW or power. All power would be

lost otherwise.

220 kV line is connected to double main and transfer busbar. This arrangement ismore economical than the one and a half scheme as it requires only one circuit

breaker with each circuit. In the event of a fault in any breaker, the circuit associated

with it can be connected to the transfer bus.

However only one circuit at a time could be connected to the transfer bus. It gives

reduced protection and restoring supply might take longer in the event of any fault if

it extends to more than one circuit and all circuits except one would go out of service.

Connecting the Transformers

The transformers are connected between the bus bars. The power rating of the

transformers depends upon the power to be handled in the bus bars. Using a

transformer with power rating much higher than the average power flowing through it

would lower the power factor. A total of three 3- transformers are installed at

Kartarpur sub-station. All three are 315 MVA, 400/220 kV, 50 Hz transformers. A

complete switchyard diagram of the 400/220 kV substation is given on the next page.

Two buses are connected via two 315 MVA, 400/220 kV, 50 Hz transformers for

voltage and current transformation.


8/25

SWITCHYARD COMPONENTS

Bay

A transmission line when enters in a switchyard in connected to a bay. A bay is

basically a collection of isolator and wave trap connected in series and CVT, LA,

earth switch connected in parallel. In sequence starting from the transmission lines

last tower and going towards the switchyard, they lie as follows: LA, CVT, WT, earth

switch, and isolator. LA comes first to protect the switchyard components from being

damaged from the sudden voltage or current surge. Then comes the CVT which, on

high voltage lines, are mostly used for the transmission of communication signals.

They send and receive these high frequency signals. WT are used for filtering out the

high frequency signals from the current as they may be outside the range of theswitchyard components which are mostly designed to operate at the frequency of or

around 50 Hz. Earth switch comes next to earth the line, if necessary. Isolator is the

last component of the bay and is used to isolate the line from the bus bar

ISOLATOR

A disconnector or isolator switch is used to make sure that an electrical circuit can be

completely de-energised for service or maintenance. Such switches are often found in

electrical distributionandindustrialapplications where machinery must have itssource 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 breakersandtransformers,and transmission lines, for maintenance. Often the

isolation switch is not intended for normal control of the circuit and is only used for

isolation

.

FIGURE 4400KV ISOLATOR
http://en.wikipedia.org/wiki/Electrical_distributionhttp://en.wikipedia.org/wiki/Electrical_distributionhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Electrical_distribution


9/25

In some designs the isolator switch has the additional ability toearththe isolated

circuit thereby providing additional safety. Such an arrangement would apply to

circuits which inter-connect power distribution systems where both end of the circuit

need to be isolated.

WAVE TRAP

Line trap also is known as Wave trap. What it does is trapping the high frequency

communication signals sent on the line from the remote substation and diverting them

to the telecom/teleprotection panel in the substation control room (through coupling

capacitor and LMU).

This is relevant in Power Line Carrier Communication (PLCC) systems for

communication among various substations without dependence on the telecom

company network. The signals are primarily teleprotection signals and in addition,

voice and data communication signals. Line trap also is known as Wave trap. What it

does is trapping the high frequency communication signals sent on the line from the

remote substation and diverting them to the telecom/teleprotection panel in thesubstation control room (through coupling capacitor and LMU).

This is relevant in Power Line Carrier Communication (PLCC) systems for

communication among various substations without dependence on the telecom

company network. The signals are primarily teleprotection signals and in addition,

voice and data communication signals.

The Line trap offers high impedance to the high frequency communication signals

thus obstructs the flow of these signals in to the substation busbars. If there were not

to be there, then signal loss is more and communication will be ineffective/probably

impossible.

FIGURE 5WAVE TRAP
http://en.wikipedia.org/wiki/Ground_%28electricity%29http://en.wikipedia.org/wiki/Ground_%28electricity%29http://en.wikipedia.org/wiki/Ground_%28electricity%29http://en.wikipedia.org/wiki/Ground_%28electricity%29


10/25

SURGE ARRESTOR

The lightning arresters provide protection against atmospheric lightening. A lightning

arrester is a protective device, which conducts the high voltage surges on the powersystem to the ground.

It consists of a spark gap in series with a non-linear resistor. One end of the diverter is

connected to the terminal of the equipment to be protected and the other end is

effectively grounded. The length of the gap is so set that normal voltage is not enough

to cause an arc but a dangerously high voltage will break down the air insulation and

form an arc. The property of the non-linear resistance is that its resistance increases as

the voltage (or current) increases and vice-versa.

The action of the lightning arrester or surge diverter is as under:

(i) Under normal operation, the lightning arrester is off the line i.e. it conducts no

current to earth or the gap is non-conducting

(ii) On the occurrence of over voltage, the air insulation across the gap breaks down

and an arc is formed providing a low resistance path for the surge to the ground. In

this way, the excess charge on the line due to the surge is harmlessly conducted

through the arrester to the ground instead of being sent back over the line.After the

surge is over, the resistor offers high resistance to make the gap non-conducting.

FIGURE 6400 KV SURGE ARRESTOR


11/25

CURRENT TRANSFORMER

Current transformer (CT) is used for measurement of electric currents. When current

in a circuit is too high to directly apply to measuring instruments, a current

transformer produces a reduced current accurately proportional to the current in thecircuit, which can be conveniently connected to measuring and recording instruments.

A current transformer also isolates the measuring instruments from what may be very

high voltage in the monitored circuit. Current transformer has a primary winding, a

magnetic core,and a secondary winding. A primary objective of current transformer

design is to ensure that the primary and secondary circuits are efficiently coupled, so

that the secondary current bears an accurate relationship to the primary current.

The most common design of CT consists of a length of wire wrapped many times

around a silicon steel ring passed over the circuit being measured. The CT's primary

circuit therefore consists of a single 'turn' of conductor, with a secondary of manyhundreds of turns. The primary winding may be a permanent part of the current

transformer, with a heavy copper bar to carry current through the magnetic core.

Shapes and sizes can vary depending on the end user.

FIGURE 7

400 KV CT
http://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_core


12/25

CAPACITIVE VOLTAGE TRANSFORMER

The potential transformer are basically step-down transformers. The connections of

voltmeter when used in conjuction with the potential transformer for measurement of

high A.C. voltages. The voltage to be measured is applied across the primary windingwhich has a large no. of turns is coupled magnetically to the primary winding. Turn

ratio is so adjusted that the secondary voltage is 110V when full rated primary voltage

is applied to primary.

Potential transformers are used to operate voltmeter, the potential coils of

wattmeter and relays from high voltage lines. The design of potential transformer is

quite similar to that of power transformer. But the loading capacity of a potential

transformer is very small in comparison to that of power transformer. The loading of a

potential transformer some time is only a few volt amperes. These transformers are

made shell type because this condition develops a high degree of accuracy. For

medium voltages i.e. upto 6.6 KV the potential transformer are usually of dry type,between 6.6 KV to 1.1 KV they may be either dry or oil immersed but for voltage

more than 11 KV they always oil immersed type. An out of door type oil immersed

voltage transformer having ratio 66000/110.

FIGURE 8

400 KV CVT

A capacitor voltage transformer (CVT) is atransformerused inpower systemsto step

downextra high voltagesignals and provide alow voltagesignal, for measurement or

to operate aprotective relay.In its most basic form the device consists of three parts:
http://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Power_systemshttp://en.wikipedia.org/wiki/Power_systemshttp://en.wikipedia.org/wiki/Power_systemshttp://en.wikipedia.org/wiki/Extra_high_voltagehttp://en.wikipedia.org/wiki/Extra_high_voltagehttp://en.wikipedia.org/wiki/Extra_high_voltagehttp://en.wikipedia.org/wiki/Low_voltagehttp://en.wikipedia.org/wiki/Low_voltagehttp://en.wikipedia.org/wiki/Low_voltagehttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Low_voltagehttp://en.wikipedia.org/wiki/Extra_high_voltagehttp://en.wikipedia.org/wiki/Power_systemshttp://en.wikipedia.org/wiki/Transformer


13/25

twocapacitorsacross which the transmission line signal is split, aninductive

elementto tune the device to the line frequency, and atransformerto isolate and

further step down the voltage for the instrumentation or protective relay. The tuning

of the divider to the line frequency makes the overall division ratio less sensitive to

changes in the burden of the connected metering or protection devices.

The device has at least four terminals: a terminal for connection to the high voltagesignal, a ground terminal, and two secondary terminals which connect 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 wound

primary voltage transformers would be uneconomical. In practice, capacitor C1is

often constructed as a stack of smaller capacitors connected in series. This provides a

large voltage drop across C1and a relatively small voltage drop across C2.

FIGURE 9

CIRCUIT-CVT

SHUNT REACTOR

The need for large shunt reactors appeared when long power transmission lines for

system voltage 220 kV & higher were built. The characteristic parameters of a line are

the series inductance (due to the magnetic field around the conductors) & the shunt

capacitance (due to the electrostatic field to earth). Both the inductance & thecapacitance are distributed along the length of the line. So are the series resistance and

the admittance to earth. When the line is loaded, there is a voltage drop along the line

due to the series inductance and the series resistance. When the line is energized but

not loaded or only loaded with a small current, there is a voltage rise along the line

(the Ferranti-effect).In this situation, the capacitance to earth draws a current through

the line, which may be capacitive. When a capacitive current flows through the line

inductance there will be a voltage rise along the line.

To stabilize the line voltage the line inductance can be compensated by means of

series capacitors and the line capacitance to earth by shunt reactors. Series capacitors

are placed at different places along the line while shunt reactors are often installed in
http://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Capacitor


14/25

the stations at the ends of line. In this way, the voltage difference between the ends of

the line is reduced both in amplitude and in phase angle.

FIGURE 10

400 KV SHUNT REACTOR

Shunt reactors may also be connected to the power system at junctures where several

lines meet or to tertiary windings of transformers. Shunt reactors contain the same

components as power transformers, like windings, core, tank, bushings and insulating

oil and are suitable for manufacturing in transformer factories. The main difference is

the reactor core limbs, which have non-magnetic gaps inserted between packets ofcore steel.

INTER CONNECTING TRANSFORMER (ICT)

Interconnecting transfomers are used to connect two EHV line at different voltages

i.e. 220KV to 400KV. The interconnecting transformer are auto transformer which

can step up & step down the voltages for synchronization of two grid voltages.

Generation of Electrical Power in low voltage level is very much cost effective.Hence Electrical Power are generated in low voltage level. Theoretically, this low

voltage leveled power can be transmitted to the receiving end. But if the voltage level

of a power is increased, theelectric currentof the power is reduced which causes

reduction in ohmic or I2R losses in the system, reduction in cross sectional area of the

conductor i.e. reduction in capital cost of the system and it also improves the voltage

regulation of the system. Because of these, low leveled power must be stepped up for

efficientelectrical power transmission.This is done by step up transformer at the

sending side of the power system network. As this high voltage power may not be

distributed to the consumers directly, this must be stepped down to the desired level at

the receiving end with help of step down transformer. These are the use of electrical

power transformerin theElectrical Power System.
http://www.electrical4u.com/basic-electrical/index.phphttp://www.electrical4u.com/basic-electrical/index.phphttp://www.electrical4u.com/basic-electrical/index.phphttp://www.electrical4u.com/electrical-transmission/index.phphttp://www.electrical4u.com/electrical-transmission/index.phphttp://www.electrical4u.com/electrical-transmission/index.phphttp://www.electrical4u.com/http://www.electrical4u.com/http://www.electrical4u.com/http://www.electrical4u.com/http://www.electrical4u.com/electrical-transmission/index.phphttp://www.electrical4u.com/basic-electrical/index.php


15/25

FIGURE 11400/220 KV ICT

High-power or high-voltage transformers are bathed intransformer oil- a highly-

refinedmineral oilthat is stable at high temperatures. Large transformers to be used

indoors must use a non-flammable liquid. Today, nontoxic, stablesilicone-based oils

orfluorinated hydrocarbonsmay be used, where the expense of a fire-resistant liquid

offsets additional building cost for a transformer vault.

The oil cools the transformer, and provides part of the electrical insulation between

internal live parts. It has to be stable at high temperatures so that a small short or arcwill not cause a breakdown or fire. To improve cooling of large power transformers,

the oil-filled tank may have radiators through which the oil circulates by natural

convection. Very large or high-power transformers (with capacities of millions of

watts)may have cooling fans, oil pumps. Oil transformers ar equipped withBuchholz

relays.

BUCHHOLZ RRELAY

Buchholz relay is a safety device mounted on oil-filled power transformers and

reactors,equipped with an external overhead oil reservoir called a conservator. On a

slow accumulation of gas, due perhaps to slight overload, gas produced bydecomposition of insulating oilaccumulates in the top of the relay and forces the oil

level down. A float switch in the relay is used to initiate an alarm signal. If an arc

forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow

of oil operates a switch attached to a vane located in the path of the moving oil. This

switch normally will operate acircuit breakerto isolate the apparatus before the fault

causes additional damage. Buchholz relays have a test port to allow the accumulated

gas to be withdrawn for testing. Flammable gas found in the relay indicates some

internal fault such as overheating orarcing,whereas air found in the relay may only

indicate low oil level or a leak .
http://engineering.wikia.com/index.php?title=Transformer_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Transformer_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Transformer_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Mineral_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Mineral_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Mineral_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Silicone&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Silicone&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Silicone&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Fluorocarbon&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Fluorocarbon&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Fluorocarbon&action=edit&redlink=1http://engineering.wikia.com/wiki/Watthttp://engineering.wikia.com/wiki/Watthttp://engineering.wikia.com/index.php?title=Buchholz_relay&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Buchholz_relay&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Buchholz_relay&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Buchholz_relay&action=edit&redlink=1http://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Reactance_%28electronics%29http://en.wikipedia.org/wiki/Reactance_%28electronics%29http://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Float_switchhttp://en.wikipedia.org/wiki/Float_switchhttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Arcinghttp://en.wikipedia.org/wiki/Arcinghttp://en.wikipedia.org/wiki/Arcinghttp://en.wikipedia.org/wiki/Arcinghttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Float_switchhttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Reactance_%28electronics%29http://en.wikipedia.org/wiki/Transformerhttp://engineering.wikia.com/index.php?title=Buchholz_relay&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Buchholz_relay&action=edit&redlink=1http://engineering.wikia.com/wiki/Watthttp://engineering.wikia.com/index.php?title=Fluorocarbon&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Silicone&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Mineral_oil&action=edit&redlink=1http://engineering.wikia.com/index.php?title=Transformer_oil&action=edit&redlink=1


16/25

CIRCUIT BREAKER

A circuit breaker is an automatically operated electricalswitchdesigned 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 immediatelydiscontinue 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, from small devices that

protect an individual household appliance up to largeswitchgeardesigned to protect

high voltage circuits feeding an entire city.

The circuit breaker must detect a fault condition; in low-voltage circuit breakers this

is usually done within the breaker enclosure. Circuit breakers for large currents or

high voltages are usually arranged with pilot devices to sense a fault current and to

operate the trip opening mechanism. The tripsolenoidthat releases the latch is usually

energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control powersource. 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 havesolenoidsto

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 (opening) the

circuit. Contacts are made of copper or copper alloys, silver alloys, and other highlyconductive materials. Service life of the contacts is limited by the erosion of contact

material due to arcing while interrupting the current. Miniature and molded case

circuit breakers are usually discarded when the contacts have worn, but power circuit

breakers and high-voltage circuit breakers have replaceable contacts. 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,oroilas the medium in which the arc forms.

Electricalpower transmissionnetworks are protected and controlled by high-voltage

breakers. The definition of high voltagevaries but in power transmission work is

usually thought to be 72.5 kV or higher, according to a recent definition by

theInternational Electrotechnical Commission(IEC). High-voltage breakers are

nearly alwayssolenoid-operated, with current sensingprotective relaysoperated

throughcurrent transformers.Insubstationsthe protective relay scheme can be

complex, protecting equipment and buses from various types of overload or

ground/earth fault.
http://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Overcurrenthttp://en.wikipedia.org/wiki/Overcurrenthttp://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Fuse_%28electrical%29http://en.wikipedia.org/wiki/Fuse_%28electrical%29http://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Insulating_gashttp://en.wikipedia.org/wiki/Insulating_gashttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Insulating_gashttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Fuse_%28electrical%29http://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Overcurrenthttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electricity


17/25

High-voltage breakers are broadly classified by the medium used to extinguish the

arc.

Bulk oil Minimum oil

Air blast

Vacuum

SF6

In 400/220 KV Kartarpur sub-station of PGCIL, the circuit breakers used are of SF6

type only, due to the nature of high rating lines.

SF6 CIRCUIT BREAKERS

SF6 GAS

Sulfur Hexafluoride (SF6) is an excellent gaseous dielectric for high voltage power

applications. It has been used extensively in high voltage circuit breakers and other

switchgears employed by the power industry. Applications for SF6 include gas

insulated transmission lines and'gas insulated power distributions. The combined

electrical, physical, chemical and thermal properties offer many advantages whenused in power switchgears. Some of the outstanding properties of SF6 making it

desirable to use in power applications are :-

V High dielectric strength

V Unique arc-quenching ability

V Excellent thermal stability

V Good thermal conductivity

FIGURE 12SF6 ARC QUENCHING
http://en.wikipedia.org/wiki/Sulfur_hexafluoridehttp://en.wikipedia.org/wiki/Sulfur_hexafluoridehttp://en.wikipedia.org/wiki/Sulfur_hexafluoridehttp://en.wikipedia.org/wiki/Sulfur_hexafluoride


18/25


19/25

D- Arc extinction. The current approaches zero and the gas from the self-blastvolume blasts up through the nozzle, cooling the arc and extinguishing it.

Excessive pressure in the puffer volume is released through the pressure relief

valve.

E- The contacts are now fully open; the motion has been damped and stopped by

the operating mechanism.F- During closing the contacts close and the puffer volume is refilled with cold

gas, making it ready for the next opening operation.

ABB 400 KV SF6 CIRCUIT BREAKER

1-Upper Terminals2. Porcelain Insulators3. Lower Terminals4. Lifting Hooks5. Supporting Structure6. Cabinet7. Inspection window8. Cross-Angles


20/25

IMPORTANT TECHNICAL SPECIFICATIONS OF CIRCUIT BREAKER

1- Type of circuit breaker : SF6.2- Number of Poles : Three (3).

3- Rated Voltage : 420 KV (rms)

4- Corona extinction voltage : 320 KV (rms)

5- Rated frequency : 50 Hz.

6- Rated Normal Current : 2500 A at amb. & 3150 at 50 c

7- Total break time : Maximum 50 ms.

8-Total closing time : Maximum 160 ms.

9- Pre-insertion resistance : 400 Ohms (Required for

line breaker only)

10-Short time current : 40 KA for 3 second at Carrying capability rated voltage.

11- Out of phase breaking : 10 KA (rms.) Current capacity.12- First pole to clear factor : 1.3

PICTORIAL -STEPWISE VIEW OF SERVICING OF SF6

CIRCUIT BREAKER

FIGURE 13

SWITCHYARDSF6 BREAKER BASE UNIT


21/25

FIGURE 14

OPENING OF SF6 FOR SERVICING

FIGURE 16

MOVING CONTACTS SF6 BREAKER


22/25

FIGURE 17

OUTER CASING SF6 ARMS

FIGURE 18

FIXED CONTACTS -SF6 BREAKER

TESTING OF ABB SF6 BREAKER


23/25

Dynamic Contact Resistance Measurement for CB healthiness

By application of Dynamic Contact Resistance Measurement, condition of arcing

contact, main contact, operating levers, driving mechanism can be predicted. If

DCRM signature shows vide variations and also there is change in arcing contact

insertion time, it indicates erosion of the arcing contacts to main contacts and

subsequent failure.

Contact Travel Measurement

Transducers are attached to the operating rod or interrupting chamber in order to

record the contact travel. When CB closes, contact travel is recorded. Contact bounces

or any other abnormality is also clearly indicated by the Contact Travel Measurement.

If contact travel, contact speed and contact acceleration signature are compared withthe original signatures, then it may indicate problems related with the operating

mechanism, operating levers, main/ arcing contacts, alignments etc.

DCRM along with Contact Travel measurement is useful in monitoring length of

Arcing contacts. Erosion of Arcing contacts may lead to commutation failures and

current may get transferred to Main contacts. Due to heat of arc, main contacts may

get damaged.

FIGURE 19

SETTING UP OF DCRM KIT


24/25


25/25

REFERENCES

[1] PGCIL official site

[2] Power System Analysis, Glover Sarma

[3] Power System Engineering, Nagrath Kothari

[4] ABB Circuit breaker operational manual

power grid corporation of india 400 220 kv vocational training report

Documents