Interview Questions Answers in Electrical Engineering

Question { 2274 }

In case of a synchronous generator carbon brushes, some
brushes expire before the others. Why is so? When all the
brushes are installed at the same time, why don't thee
expire at the same time?

Answer

That depends on shape of the brush holder and spring pressure on each brush

Is This Answer Correct ?

0 Yes

0 No

Question { 4066 }

What is the minimum setting in REF relay because i am
facing some problem whenever power resumes after power
failure my transformer is tripping because of REF trip. I
am using CSPC make numerical relay(DIP switches). Now
setting is 15 percentage. What is the reason for this
triping. I sm waiting for answer

Answer

Increase the time delay

Is This Answer Correct ?

0 Yes

0 No

Question { TVS, 13440 }

Why the earth terminal pin is larger than phase and neutral
in three pin plug top>

Answer

You can insert the top in one way only ,so that the phase
and neutral wires are not interchanged and also because the
earth fault current could be higher than the load current

Is This Answer Correct ?

2 Yes

3 No

Question { Appco, 33158 }

what is the disadvantage of leading power factor...why can't
we use it (pf=0) for a long period of time?

Answer

In case of load,it will result in negative voltage
regulation increasing the voltage.In case of generators it
has the de-stablizing effect on the system ,the pf of which
is always lagging.

Is This Answer Correct ?

20 Yes

2 No

Question { BARC, 12415 }

is starting current of induction is high or stating current
of ransformor is hign ,for the same rating

Answer

Indction motor ,as the starting current is initial
magnetising current plus the current required to overcome
the inertia of the rotor

Is This Answer Correct ?

1 Yes

0 No

Question { 3098 }

Why do we choose 33kV transmission for industrial purpose
and 11Kv for township?

Answer

You get enough space to construct a 33KV substation inside
the factory premises

Is This Answer Correct ?

0 Yes

2 No

Question { Bhel, 11981 }

what is relay type VDG,CDG,VTT ect?

Answer

Generally V =voltage ,D = disc type ,G =IDMT ,T= trip
circuit ,C= current.Hence VDG may be under/over voltage disc
operated IDMTL relay.CDG similarly current relay.VTT could
be voltage operated trip circuit supervision relay.

Is This Answer Correct ?

10 Yes

1 No

Question { 2935 }

What is the current carring capacity of 0000SWG and 0SWG
overhead solid bare copper conductor. If possible please
provide reference for various sizes Vs current ratings

Answer

The diameter is 9.98 mm (app)

Is This Answer Correct ?

0 Yes

0 No

Question { 28280 }

why we use stones or rock pieces in transformer area?

Answer

Granite aggregate is spread around Tr plinth to 1.prevent
vegetation 2 reduce both touch and step voltages 3 provide
an antiskid surface

Is This Answer Correct ?

2 Yes

1 No

Question { 4850 }

how to caculate no load loss, load losses & impedance
percentage in power or distribution transformers

Answer

Short the LV side ,increase voltage on HV ,till you get the rared current. The percentage of this voltage against rated voltage is % impedance . if you connect a watt meter you get copper losses . With open circuit apply rated voltage ,to measure the iron losses with a watt meter .

Is This Answer Correct ?

0 Yes

0 No

Question { NTPC, 11938 }

1.what type of oil used in tranformer.
2.oil vesocity.
3.oil gauge.
4.witch time oil filterring & how much temperature
maintaned.

Answer

1. Mineral oil-commonly called as Tr oil
2. 27CST (max)
3. ?
4.a) BDV is below 30KV for voltage below 72.5 Kv,40Kv for
voltage 72.5-170 Kv and 50Kv for above 170 Kv b)water
content above 20 ppm for above 170 Kv and40 ppm for below
170 Kv c) PI value less than 1.2 Temperature to be
maintained while filtering is 65- 70 C at almost full vacuum

Is This Answer Correct ?

3 Yes

1 No

Question { 2517 }

A powerplant has 8 gensets operating in grid parallel
mode. In one genset sometimes there is pf variation and kvar
variation. The plant operates in pf mode. When this
variation is onbserved the load is stable, voltage is also
stable, freq and genset speed is also stable. How will you
check the functioning of pf card. What shall be the ideal
output vdc of the pfc, from there it is input to AVR?

Answer

When it is in parallel with 7 other generators , its voltage and frequency(speed )are decided by the grid . hence its pf card is faulty as there no variation in shared load. Exchange the pf cards and confirm

Is This Answer Correct ?

0 Yes

0 No

Question { 5087 }

What is the range of the stator resistance of 3 phase
induction motor?

Answer

In case of squirrel cage it is almost zero and in rotor
wound, it depends on HP.It decreases with HP.

Is This Answer Correct ?

1 Yes

2 No

Question { 3145 }

my N-P 230 VAC at 3 wires but i haven't any voltages at phase
to phase whither my supply is 3 phase, why i haven't received
these line to line voltages ?

Answer

The live wires are connected to the same phase

Is This Answer Correct ?

1 Yes

0 No

Question { 2374 }

what happens if we earth negative electrode of an
rectifier transformer used in ESP. In which normaly
positive is earthd from inside the xmer.

Answer

Nothing ,you can earth any polarity

Is This Answer Correct ?

0 Yes

0 No

k.prakashchandra