Interview Questions Answers in Electrical Engineering

Question { 4058 }

why using carbun
bresh in dc motor

Answer

The other reason is that carbon powder is also a lubricant.
This reduces the wear on the commutator.

Is This Answer Correct ?

1 Yes

0 No

Question { Bhel, 4003 }

whether choke act as a voltage regulator in tubelight or not?

Answer

It acts to limit the current flow. When the tube lights up
the gas in the tube has very low resistance and n the choke
stops too much current from going through the tube.

Is This Answer Correct ?

0 Yes

2 No

Question { 2525 }

how i run d.c. moter with solar panel without use of battery?

Answer

This is possible but the voltage on the motor will change
with the sunlight.
A voltage regulator could get a constant voltage but the
motor will only operate when the sun is shining.

Is This Answer Correct ?

0 Yes

2 No

Question { 5578 }

what is the difference in between short time and continuous
rating?

Answer

Machines are designed to be able to run at a maximum load
continuously.
With some machines there is a overload capacity. This means
fo a short time they can carry a higher load the the normal
maximum.
Short time rating may be stated as something like 1 hour in
24 hours. This is because more heat is produced when
overloaded and if the machine is not given time to cool
down it will fail.

Is This Answer Correct ?

2 Yes

0 No

Question { 2834 }

why capacitor do not switch ON the DG power? (I had checked, capacitor ON in DG power that time current rating was reduced.)

Answer

Because it does not help the DG. The reduced current is
reactive only and does not load the engine.
If there is too much capacitance the DG can get a leading
power factor and if this is too great lose control of the
voltage.
In the grid capacitors are used to get the power factor
closer to unity and reduce the current. This means the
power lines can be smaller. If the power factor is leading
it is OK because others will have a lagging power factor to
balance it.

Is This Answer Correct ?

0 Yes

0 No

Question { 2545 }

why is neccessary Tap changing of power transformer with in a
certain time

Answer

Tap changing is to change the ratio of the input voltage to
the output voltage. This changes the output voltage.
When the load on a power line changes the voltage changes
as well because of a reduced or increased line losses.
The tap changing means the output voltage can be controlled
to be as close to the desired voltage. Otherwise serious
high or low voltage could be experienced.

Is This Answer Correct ?

1 Yes

0 No

Question { Bhel, 4622 }

what is RTD? what is THERMOCOUPLE? What is difference between
it?

Answer

An RTD is a resistance temperature detector. It works by
measuring the changing resistance of the element as the
temperature changes.
A thermocuople is a joint between two different metals whic
produce a voltage which changes with temperature.

Is This Answer Correct ?

6 Yes

1 No

Question { 4099 }

how to identify 3phase....r y b .A new make altnator how
to identify R

Answer

On a new alternator the markings are usually U V W N
These match to R Y B N.
But it may be that the phase rotation in the building is
backwards and all the 3 phase motors will then run
backwards on the new alternator supply.
A phase rotation meter should be used to confirm that the
phase rotation is identical.

Is This Answer Correct ?

1 Yes

0 No

Question { Qatar Airlines, 6235 }

Why is it that polarization index type test is required for
MV and HV motors and not for LV motors?

Answer

The polarisation index is used to check the insulation of
MV and HV motors because it is more accurate. Also it
allows a lower voltage than the working voltage of the
motor to be used. In LV motors the megger test is usually
twice the working voltage. If this was used on an 11kv
motor the megger would need to be 22kv.

Is This Answer Correct ?

4 Yes

0 No

Question { 6584 }

why we somewhere use ryb
phase sequance, somewhere
use uvw, and somewhere abc??

Answer

RYB is for the phase colours Red Yellow Blue the usual
colours used for ther insulation.
ABC is an old standard
UVW is from a newer standard

Is This Answer Correct ?

0 Yes

0 No

Question { 3939 }

why we are connecting the alternator to a steam turbine of
higher RPM then the rated RPM of alternator?
For example:( connecting 1500 rpm alternator to 7600 rpm
steam turbine). we can directly connect the same rpm
turbine to alternator know??? is there any special reason ???

Answer

An alternator cannot be built to run faster that 3000 rpm
if it is to produce 50 Hz. and often is made to run at
1500RPM.

Turbines are not efficient at those low speeds so they are
operated at higher speeds and gearing must be used to
change the speed down to the maximum speed of the
alternator.

Is This Answer Correct ?

1 Yes

0 No

Question { ABB, 32520 }

what is the meaning write of AC1,AC2,AC3 .....power contactor

Answer

They are the ratings of the contactor.

AC1 is for resistive loads and AC3 is for normal motor
loads. AC2 is for special conditions of motors.

Is This Answer Correct ?

27 Yes

5 No

Question { 2624 }

what is relation between motor poles & motor current in 3
phase motor

Answer

The current has no relationship with the number of poles.
The speed of rotation is dependant on the poles. The more
pairs of poles the slower the motor rotates.

The current is dependant of the mechanical load on the
motor.

Is This Answer Correct ?

2 Yes

0 No

Question { Maruti Suzuki, 3634 }

What are the safety devices on Cumins Diesel Generators
from 500 kva to 1500 kva.

Answer

It will depend on the controller used.

Most sets have at least-
Low oil pressure,
High engine temperature,
Low coolant level,
Over speed,
Under Speed,
Low AC volts,
High AC volts,
Over current,
Short circuit,
Weak battery,

Paralleling sets will also have-
Reverse power,
Loss of excitation,
Phase rotation,
Synch check,
Braeker fail to close,

Is This Answer Correct ?

4 Yes

0 No

Question { 4439 }

My ups output shows 230 v between phase and neutral,but show
zero between phase and earth.Is the system/installation is
correct.If not what will be the possible reasons

Answer

There is no connection between the earth and neutral. This
can be because there is and isolated earth system or
someone did not connect it correctly.

Is This Answer Correct ?

2 Yes

0 No

kurt jorgensen