SWITCHGEAR AND PROTECTION SCHEME IN 132/33 KV SUBSTATION----by v.sai bhargav, india

7/31/2019 SWITCHGEAR AND PROTECTION SCHEME IN 132/33 KV SUBSTATION----by v.sai bhargav, india

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SWITCHGEAR AND PROTECTION SCHEME IN132/33 KV SUBSTATION

Department of Electrical and Electronics Engineering Gokula Krishna College of Engineering

MINI PROJECT PRESENTED BY

V.SAI BHARGAV (08F81A0235)

G. PRAVEEN KUMAR (08F81A0226)

K.SRIDHAR (09F85A0204)

U.SATHISH (08F85A0237)

V,RAMANAIAH (09F85A0202)


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ABSTRACTOne hour halt in supply = 5 lakh crore losses in USA. so to avoidlosses (in industrial sector, commercial sector etc,) continuity insupply should be ensured .India is lagging in supplying quality power relative to countries like

Denmark, Sweden, Japan, etc, even we are at 6th

position in world,in consuming power (3.4 % share)So we studied switchgear and protection ( SGP) scheme in 132/33 kvNaidupeta substation which detects, clears fault as fast as possibleto ensure continuity in supply.


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SWITCHGEAR AND PROTECTION

It consists of relays, circuit breakers and associated auxiliariesfor controlling ,regulating, switching the electrical circuits inpower system.

In AP Transco mostly SF6

circuit breaker is used at HV side andVCB on LV side.90% of all operations are by primary protection and 10% bybackup protection ( in case primary protection fails).


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SF6 CIRCUIT BREAKER

Here SF 6 gas is used as arc quenching medium, it absorbs free electronsdue to its inert, thermally stable and electronegative nature.Used at HV side due to its current carrying capability( 1.5 times thanVCB),small arcing time , etc.


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Opening operation :- As stationary and moving arcing contacts separates ,arc generates. The gas pressure in puffer cylinder builds up and powerfulgas flow quenches the arc.Closing operation :- Here insulating rod is pushed up and all parts move inthe reverse order of opening operation.


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SPRING OPERATING MECHANISMTrip holding latch and trip trigger blocks the counterclockwise torquereceived by lever A and B. So contacts is closed position.Opening signal rotates trip holding latch clockwise ,which rotates lever B ,so contact opens.


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VACUUM CIRCUIT BREAKER

In VCB, vacuum provides arc quenching mediumTo close/open the circuit breaker ,control elements are actuatedelectrically or mechanically.This enables , spring energy mechanism , through linkage system , to close

/open the breaker. The two options for charging are1. by electric motor (electrically)2. by manual operation (mechanically)


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MANUAL OPERATIONFor charging the closing springs manually. fully insert the charging handleinto the seat and rotate it clockwise.As the spring gets charged , a sound ( internal latches getting engaged )can be heard .The force which can be normally be applied to the charging handle is 130N. In any case , the maximum force applied must not exceed 170 N.


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BY ELECTRIC MOTORHere spring charging device is operated by geared motor. The system hashelical tension spring for closing and opening.An indication shows whether the closed spring is charged or not. The

number of opening operations are counted by counter.Close or open operations are done by charging /discharging the closing ortripping springs through linkage mechanism via geared motor and otherassembly.


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PROTECTIVE RELAYING

Fault is first sensed by relay through CT, in turn close tripcircuit of breaker(when ever more current flows) makingcircuit breaker open.

Buchholz relay is used for T/F protections. For low faults alarmsounds, for serious faults T/F (oil immersed) is totallyseparated from supply.

Distance relay operates when V/I ratio is less than predetermined value


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AUXILLIARIES

Isolators are employed for isolating circuit (under no load)careless opening leads to arcing, flashover to ground.Instrument T/Fs provides current and voltage required toactuate relays, insulation against high voltage power circuitand protects apparatus, personnel from high voltage.For safety purposes secondary's of CTs,PTs are grounded

Instrument transformers Primary rating Secondary rating

Current T/F 10-3000 A 0.1-5 A

Potential T/F > 400 V 110 V or 1103 V


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Fuses and lightening arrestors

Fuses are used at different areas of substation ,its actiondepends on heating effect,Lightening arrestors are connected between line and earthsuch that it diverts incoming high voltage wave to earth.Power transformers are used to step up/down the voltage ,oilnatural air forced type is used in Naidupeta substation.


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Batteries and earthing

110 Lead-acid batteries (DC voltage) connected in series areused ,each contributes 2V. These are charged with 220V Ac.Here plate earthing is used. Earthing plate (copper orgalvanized iron) is buried at a depth 3 meters with alternatelayers of coke and salt.Tap is provided above earthing to keep the place wet.


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conclusion

Switchgear and protection devices plays vital role in reducinghazards and ensures continuous supply, by fastly respondingto faults .

Day by day newer designs ,automatic and maintenance freeSGP devices are developing ,thus ensuring more quickeroperations for interruption free supply.


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SWITCHGEAR AND PROTECTION SCHEME IN 132/33 KV SUBSTATION----by v.sai bhargav, india

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