OPERATIONS UNDER ABNORMAL CONDITIONS

The following instructions are intended to serve as guidelines for

carrying out operations in 110KV substation. The operations are required to fully understand the situations before proceeding on with operations.

A. Tripping of 11KV feeders(at HT panel breakers)

Conductor used in 11KV feeders is RACOON. It has 197A capacity. CT ratio of 11KV feeder CTs is 200/5. Over current setting is 200A. Earth fault current setting is 20A.

1. Accept and reset the alarm, note down the name of feeder tripped and time of tripping and note down the relay

indications.

2. Reset the relays and test charge the feeder after 3 minutes if the operator feels that the fault is not heavy. In case of a heavy fault don’t test charge the feeder and declare the feeder as faulty and pass the message to the concerned electrical sections.

3. If the feeder trips again, accept the alarm and note down the relay indications after accepting alarm. Reset the relays and declare the feeder as faulty. Inform the matter to the immediate custodian of the line.

4. If the feeder is found to be healthy on test charging please check the phase currents to ensure balanced loading.

NOTE: operators are expected to judge the sound of tripping and the voltage dip at the time of dripping. Heavy dip in voltage and loud

tripping sound indicate very high faults. Operators need not test charge the feeder under such circumstances. The feeder can be declared faulty straight away. Do not forget to note down the reason for not test

charging the feeder. Before declaring any feeder faulty, ascertain the

health of the substation equipments. First carry out a visual examination of all the equipments. Open the AB switch of the line in DP structure.

Charge the feeder up to the structure. If ok, switch off the breaker and declare the feeder faulty. If the breaker trips, do not charge it again.

Inform the matter to the station engineer and the assistant executive engineer.

B. Tripping of 110KV feeders

Conductor used in 110KV feeders is WOLF. It has 343A capacity. CT ratio of 110KV feeder CTs is 400/1. Over current setting is 400A. Earth fault current setting is 80A.

1. Note down the name of the feeder and the time of tripping; accept the alarm and note down the relay indications.

2. If distance relay is acted, note down the zone of fault and contact the operator at the other end and note down the indications on the other end.

3. If the zone of fault is other than zone 1 at this end. Test charging may be attempted in consultation with station engineer.

4. If both feeders trip on the fault, Switch off all the outgoing 11 KV feeders except the station auxiliary and follow the above steps.

C. Tripping of 110KV breaker of any one of the transformers 12.5MVA 110/11KV transformers have a primary CT ratio of 100/1 and secondary CT ratio of 600/5. Their primary over current setting is 65A and secondary over current setting is 600A. Their primary earth fault setting is 20A and secondary earth fault setting is 120A.

1. Note down the time of tripping, accept and reset the relays after noting down the indications

2. Switch off all outgoing feeders fed from that transformer.

3. If the transformer has tripped on Buchholz or differential relay do not reset charge it. Inform the station engineer and assistant

executive engineer.

4. In other cases, check the reason for tripping. Inspect the concerned equipments, cables etc. if everything found normal, test charge the transformer from 110KV side in consultation with station engineer.

If normal, load the transformer by closing the 11KV breaker.

Charge all outgoing feeders one by one.

N.B: If the transformer could not be charged for a long duration, the outgoing feeder can be supplied from the other transformer (ensure that the single transformer can cater the entire load)

In the case of 110/11KV transformer, rack in the bus coupler and charge after switching off the incomer of the faulty transformer.

D. Tripping of both 110/11KV transformers simultaneously

1. Note down the time of tripping, accept the alarm and reset the relays after noting down the indications.

2. If the transformer has tripped on Buchholz or differential relay do not test charge it. Inform the station engineer and the assistant executive engineer.

3. Switch off all the outgoing feeders fed by the transformer and physically inspect the station equipments and cables for any damages.

4. If everything is found ok, test charge the transformer. If normal, load the transformer by charging the feeder one by one. If the transformer trips when any one of the feeder is charged, it may be the breaker of the feeder, which failed to clear the fault. Isolate that feeder and charge the

transformer and feeders one by one. Inform the matter to the station engineer and assistant executive engineer.

NOTE: When the 110KV breaker of the transformer trips on Buchholz or differential relay then its 11KV breaker is also expected to trip.

E. Failure of 110KV supply(Breaker not tripped)

1. Switch off all the outgoing 11KV feeders except the station auxiliary. Switch off battery charger input and output. Contact O/D, of the certain incoming feeder’s substation and ascertain the nature of the failure.

2. Confirm that no breaker of the substation had tripped

simultaneously. If a breaker had tripped, it may be the reason that the 110KV line tripped because of the severity of the fault in this circuit. Check distance relay to see indications.

3. If the supply is resumed, charge all feeders one by one after

ascertain the readiness of the system to accept the load and switch on the battery charger input and output. If the supply fails again (when breakers are being charged), it shows that this particular breaker failed to clear a fault. Inform the station engineer and the assistant executive engineer.

F. Issuing PW on 110/11KV transformer and incomer

Before issuing the PW ensures that the 11KV load on the station is within the safe loading capacity of the other transformer.

1. Rack in and switch on the bus coupler to enable the sharing of load by transformers and to ensure the interruption free supply to the consumers.

2. Switch off the breakers of the 11KV incomer on which the PW is required.

3. Switch off the 110KV breakers of the transformer on which this incomer is connected.

4. Open the isolator on the 110KV side of the transformer and ensure that all isolator blades are separated correctly.

5. Rack out the incomer 11KV breaker already in switched off condition.

6. Earth both HV and LV side transformer on which the PW being issued.

7. Mark safe operating area using tape and display necessary danger boards both at yards and at the respective panel in the control room.

8. Issue PW

Authority to take permit: Officer not below the rank of assistant engineer

G. Cancelling PW on 110/11KV transformer and incomer

1. The PW can be cancelled only at the request of that person who has taken permit.

2. Take out the danger boards and the tape for marking safe operating are.

3. Disconnect the earthing provided on HV and LV sides of the transformer.

4. Rack in 11KV breaker of the incomer.

5. Close the 110KV isolator at yard and ensure the correctness of contact.

6. Switch on the 110KV breaker of the transformer after ensuring that taps of the both transformers are in same position. Before doing this ensure that all persons have come out of yard.

7. Switch off 11KV breaker of the incomer.

8. Switch off and rack out the bus coupler.

H.Issuing switch off confirmation(soc) on 11KV lines a. When SOC is requested over phone

1. Note down the time of call and phone number from which the call is made. Ensure that it is from the person who is authorized for taking permit on that particular line. Note down the work,

location of work for which permit is required and approximate duration of work.

2. Switch off the breaker of the feeder on which SOC is required.

3. Rack out the breaker from the bus and display SOC board.

4. Issue SOC on the feeder with SOC No. date and time, reading overall the operations done and exchange code words with the instruction to provide local earthing.

b. When SOC is requested in person

1. Ensure the authority of the person came for taking permit.

Note down the work, location of the work for which permit is required and approximate duration of work.

2. Switch off the breaker of the feeder on which the SOC is required.

3. Rack out the breaker from the bus and display the SOC board.

4. Issue SOC on the feeder with SOC No. date and time, reading over all the operations done with the instruction to provide local earthing and get sign in the SOC certificate.

Authority to take SOC: - Officer not below the rank of sub engineer, 110KV substation and officers not below the rank of the sub engineer of custodian sections. SOC can be issued to officers not below the rank of the sub engineer of concerned electrical sections after getting permission from custodian.

I. Returning switch off confirmation (SOC) on 11kV lines a. For SOC is requested over phone.

1. Note down the time of call and phone number from which the call is made. PERMIT CAN ONLY BE RETURNED ON THE REQUEST OF THE PERSON WHO HAS

TAKEN THE PERMIT. Verify the correctness of SOC No.

, date, time and the code words at the time of returning.

2. Take out the display board and rack in the breaker of the feeder.

3. Charge the breaker of the feeder after one more confirmation.

b. For SOC is requested over a person

1. PERMIT CAN ONLY BE RETURED ON THE

REQUEST OF THE PERSON WHO HAS TAKEN THE PERMIT. Verify the correctness of SOC No. , date, time and get signed in SOC cancellation.

2. Take out the display board and rack in the breaker of the feeder.

3. Charge the breaker of the feeder after one more confirmation.

N.B:- Ensure the load balance after charging the feeder. If there are more than one permit issued on the 11 KV feeders, that much number of SOC boards should be displayed and the feeder can be charged only after returning all SOCs.

J. Issuing blink on 11KV lines.

1. Switch off the 11KV feeder on which blink is requested. Note down the name of AB switch which is to be operated.

2. Charge the 11KV feeder on the returning the blink. Note down the load of the feeder after charging. Ensure the load balance.

Authority to take the blink: officers not below the rank of the sub engineers in concerned electrical sections.

K. Issuing PW on 110KV lines

a. When PW is requested over the phone

1. Note down the time of call and phone number from which the call is made. Ensure that it is from the person who is authorized for

taking permit on that particular line. Note down the work, location of the work for which permit is required and the approximate time of work.

2. Switch off the breaker of the 110KV feeder from this end.

3. Issue phone message to operators at 110KV substation at the other end to switch off and isolate the feeder at that end.

4. Open the isolator of 110KV feeder after getting confirmation message from concerned 110KV substation at the other end.

5. Obtain the non back feeding from the O/D at the other end substation on the same feeder.(operator at the other end has to earth the other end)

6.Close the earth switch of 110KV feeder and display necessary permit work boards both at yard and panel at the control room.

Mark safe operating area using tape if the work is on the yard equipments.

7. Issue PW feeder with PW no. date and time, reading over all the operations done and exchange code words.

b. When PW is requested in person

1. Ensure the authority of the person came for taking permit Note down the work, location of the work for which permit is required and approximate time of work.

2. Switch off the breaker of 110KV feeder from this end.

3. Issue phone message to operators at 110KV substation at the other end to S/OFF and isolate the feeder at that end.

4. Open the isolator of 110KV feeder after getting confirmation message from concerned 110KV substation at the other end.

5. Obtaining Non back feeding from O/D at the other end substation on the same feeder(operator at the other end has to earth the other end)

6. Close the earth switch of 110KV feeder and display necessary permit work boards both at yard and panel at the control room.

Mark safe operating area using tape if the work is on the yard equipments.

7. Issue PW feeder with PW no. date and time, reading over all the operations done.

L. Cancelling PW is requested over phone a. When PW is requested over phone.

1. Note down the time of call and phone number from which the call is made, PERMIT CAN ONLY BE RETURNED ON THE

REQUEST OF THE PERSON WHO HAS TAKEN PERMIT.

Verify the correctness of PW No., date, time and the code words at the time of returning.

2. Open the earth switch of the feeder.

3. Issue phone message to the operator at the other end to return the NBC issued.

4.After receiving NBC cancellation message (the operator at the other end has to remove earth switch and close the line isolator) close the line isolator at this end.

5.Remove all the danger boards and charge the feeder by closing the breaker at this end and inform the same at the other end.

b. When PW is requested directly

1. PERMIT CAN ONLY BE RETURNED ON THE REQUEST OF THE PERSON WHO HAS TAKEN THE PERMIT. Verify the correctness of PW No. , date and time and get signed in PW cancellation.

2. Open the earth switch of the feeder.

3. Issue the phone message to operator at the other end to return NBC issued.

4. After receiving the NBC cancellation message, close the line isolator at this end.

5. Remove all the danger boards and charge the feeder by closing the breaker at this end and inform the same at the other end.

CONCLUSION

Working at the 110kV substation as summer training was a very nice experience. I learned a lot about electrical substation system and the importance of substations in electrical generation, transmission and

distribution. This industrial visit provided an insight on how substations work and thus helps in efficient transmission of electricity. We also studied about different substation equipments in detail. It has given us useful information related to our course which cannot be visualized in lecture classes such as transformers which is as big as one-fourth of an average room, which we learnt about but never saw in the college labs. In the beginning of this visit I was not aware about the merits we were going to receive from the visit but at the end I realized it was a very good experience which I would have regretted if I missed. Also the training was an opportunity for me to increase my

personal relations both socially and professionally.