Interview Questions Answers in Electrical Engineering

Can we use the 60 HZ transformer/rectifier/Motors/Coils in
50 HZ? if not so, why?

Answer

Yes, but the use of 50 Hz not recomended because, this
frequnecy will give less flux linkage than what designed
for, and output voltage will be lesser.
Humming and other harmonics loss will be more/less and can
cause core heating,ie: core loss.

Is This Answer Correct ?

22 Yes

5 No

Question { Siemens, 21556 }

why contactor not provided between output of VFD and motor?

Answer

Variable frequency devises not making use of any
contactors, since the speed and rotation reverse can be
done with the circuit itself.
VFD having control of supply frequnecy and speed can be
changed with that.

Is This Answer Correct ?

32 Yes

8 No

Question { NCC, 40569 }

DIFFERENCE BETWEEN POWER AND CONTROL CABLES

Answer

Power cable mainly intend to use transfer of power,
specifically current, over a defenite length.
According to the rating there will be change in the no. of
starnds etc for a.c.

control cables are mostly paired cables ,sometimes more
flexible than power cable. and are not intend to carry more
than 10A.(max.).

Is This Answer Correct ?

39 Yes

5 No

Question { 7907 }

What is the diffrence between an ELCB(earth leakage circuit
breaker) and RCCB(residual current circuit breaker)?which
has higher degree of safety and why?

Answer

ELCB having protection against earth faults, but RCCB having
over current protection as well as earth fault protection.
So RCCB having higher degree of protection.

Is This Answer Correct ?

20 Yes

5 No

Question { Areva, 114714 }

what is the function of breather in a transformer

Answer

Breather are used to absorb the moisture content from the
sucked air, while the transformer oil gets expanded due to
heating. Breathers make use of silica gel coloured with
brown used extensively in power transformers.

Is This Answer Correct ?

233 Yes

51 No

Question { 12739 }

what is the function of conservater in transformer

Answer

Conservator is used to preserve excess oil comes out from
the transformer tank,during expansion due to heat.

Is This Answer Correct ?

23 Yes

2 No

Question { 26838 }

what is the function of cooling tubes in transformer

Answer

Cooling tubes are used for forced cooling for the transformer

Is This Answer Correct ?

12 Yes

4 No

Question { Birla, 15907 }

kindly tell me how the load on generator increase by just
increasing the fuel of prime mover, as if for exampple 20
MW gen set is synchronized the load ramps from zero to 20
MW gradully and during this procress only fuel of prime
mover increases. Which thing determines the load on
generator with respect to fuel

Answer

The load on the generator means,the line current draws from
the generator. Pls be remind that, generator is an energy
converting device, which converting mechanical energy to
electrical energy.
As soon as more current draws from the generator,the
mechanical load on the prime mover also rises. SO that, more
fuel consumption takes place.

Is This Answer Correct ?

12 Yes

1 No

Question { L&T, 113160 }

3. What is Impedance Voltage in Transformer?

Answer

Impedencce voltage is nothing but self induced voltage in
reverse direction acting against the applied voltage( across
primary)
That is why after switching ON, the current intake reduces.

Is This Answer Correct ?

51 Yes

106 No

Question { L&T, 47056 }

5. What is PMG in Alternators?

Answer

PMG is Permanent magnet generator. The alternator generaly
uses a self excited generator and converts its voltage to DC
and then applies to alternator armature windings.
this kind of alternators are named as brushless modern
alternators.

Is This Answer Correct ?

49 Yes

13 No

Question { Juniper Networks, 18561 }

HOW MANY EARTHINGS REQUIRED FOR GENERATER

Answer

Two eathing are req. minimum. Since the star point is
earthing solidly, and obviously the generator frame/housing
also to be provided with earthing to prevent any shock due
to insulation failiure.

if the generator is connected with a fuel tank, (for higher
size), it is necessary that, fuel tank to be grounted to
prevent lightning surges and any static voltage generations.

Is This Answer Correct ?

28 Yes

5 No

Question { RRB, 6806 }

what are the safety measure & controls in engine?

Answer

Safety means operator safety and engine safety.

For operator safety, there shall be an emergency shut off.
for engine safety, there shall be an overload shut off say
5times above the full load capacity after a specific time.

Controls are, speed control, torque control,fuel control,
temperature control etc.

Is This Answer Correct ?

15 Yes

2 No

Question { 9032 }

6 MVA transformer secondary is rated for 725V at no load.
The incommer ACB is rated at 690 V, 3200 Amp. Would there
be any effect on performance of ACB due to lower voltage
rating?

Answer

The transformer details shows no load voltage and we can
assume about 3-4% decrease with full load. ACB with rated
voltage 690 should not be suitable for 725V. ACB's nominal
voltage should be 1.414 time the applied voltage.

Is This Answer Correct ?

6 Yes

2 No

Question { HCL, 12648 }

how many earthing should need for UPS, where its connected

Answer

One earthing for body is well enough for single phase UPS

Is This Answer Correct ?

21 Yes

3 No

Question { KSEB, 65338 }

What is ELR, and where it is used ?

Answer

ELR is earth leakage relay, and main attraction is its high
current rating, and it can use with CT also(with suitable
calibration).
ELCB are less current capacity ELRs and using ferromagnetic
substances with differential relay.

Is This Answer Correct ?

17 Yes

15 No

roopesh