Interview Questions Answers in Electrical Engineering

Could explain briefly of over excitation in transformer.

Answer

In brief . Flux = K V / f . If the voltage increases or frequency decreases flux will increase when the other factor remains the same . That's why you can not give excitation unless the gen picks up at least 90 % of the rated speed in case of generator

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Question { 1967 }

What should do when induction motor take more load in single phase ?

Answer

Most likely , there is inter turn short in that phase . When the number of turns is reduced , the back emf and the impedance are less resulting in more current to sustain the applied voltage.

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Question { ABC, 2429 }

Double Busbar Scheme for outdoor switch yard system (132kv) step up power plant

Hi friends
1. in this system both busbars energized all the time.
2. what is the meaning of main BB and transfer BB,
3. step up transformer connect main bus bar all the time or both BB connected through DS switch .
4.bus sectionalization means ?

thank you.

Answer

When one line is connected to a BB ,the other is the transfer BB . You can energize both BB either independently or using bus coupler . Sectionalzation means splitting the bus bar into sections lengthwise

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Question { NCC, 3574 }

why transformer neutral and CT Secondary neutral is connected to earth?

Answer

Neutral is connected to earth to make available everywhere in the earth . CT secondary is earthed to remove the presence of primary voltage in the secondary due to capacitance between primary and secondary

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1 Yes

1 No

Question { Hydropower, 2344 }

Why we use CT on differant phases of 2ph.PT detection for brush-less static excitation of 3ph.,400v Synchronous Generator?
What happen if use CT on same one of VT phase?

Answer

For measurement of VAR

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Question { Hydropower, 2344 }

Why we use CT on differant phases of 2ph.PT detection for brush-less static excitation of 3ph.,400v Synchronous Generator?
What happen if use CT on same one of VT phase?

Answer

This is ' one watt meter ' method for measurement of reactive power for three phase balanced load . The current coil is connected in one line ( phase ) and the pressure coil is connected across the other two . The reactive power is root3 times the watt meter reading

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Question { 2390 }

what is RTU with SCADA connection ?

Answer

Remote Terminal Unit

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2 Yes

0 No

Question { 1906 }

LT, CC and LMU installed at both the outgoing circuits of 132 kv double ckt transmissio what its means ? and what are there use ?

Answer

These are required for PLCC . LT ( WT ) Line / wave trap , cc - coupling capacitor , LMU - Line matching unit

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Question { 2408 }

there are 3 transformers each of 1500 kva and one transformer of 1000kva for a 11 floor building . total otgoing kw is 4066 kw. i need an extra 260 kw .is there any provision for that? what is the max kw that can be connected with these transformers?

Answer

Actual capacity of tr depends on temp rise i.e. cooling

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1 Yes

0 No

Question { 2536 }

A circuit breaker on detecting fault will

a. Open

b. Close

c. Open and trigger the alarm

Answer

While opening ,its auxiliary switches 1.open the trip circuit 2. make the closing circuit active 3. make the ' auto trip indicating lamp' on.

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3 Yes

0 No

Question { HCPL, 2312 }

What the reson for frequant instantaneous ground over current fault in our sync. Generator... 15 triping in 24 hr...

Answer

This may be due to line earth fault . Disable generator instant trip due to earth fault and use only time delay of 200 - 500 ms

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0 Yes

1 No

Question { ABB, 2437 }

What is the use of Gateway RTU like ABB RTU 560 in power plant, SAS system ?

Answer

SCADA

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5 Yes

2 No

Question { 1907 }

what is the Transmission line differential protection and why differential protection also have backup Line Distance Protection ?

Answer

Generally IDMTL relays are used as back up for distance relays

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Question { 1669 }

how we could know that generator running anti clockwise with seeing the rotating direction of prime mover or engine

Answer

By increasing /dercreasing input to prime mover

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1 Yes

1 No

Question { 2098 }

what is the definition of Nominal current or voltage

Answer

As in the nameplate

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2 Yes

2 No

k.prakashchandra