Interview Questions Answers in Electrical Engineering

what are the different functions of mccb, rccb / elccb ?

Answer

MCCB ( Molded Case Circuit Breaker) - This CB used to
isolate the fault circuit while fault current >63 Amps.
(<63 Amps, we use MCB [Miniature Circuit Breaker]).

RCCB (Residual Current Circuit Breaker) - This is an
electrical wiring device that disconnects a circuit
whenever it detects that the electric current is not
balanced between the energized conductor and the return
neutral conductor.

ELCCB (Earth Leakage Circuit Breaker) - It is a safety
device used in electrical installations with high earth
impedance to prevent shock.

Is This Answer Correct ?

7 Yes

1 No

Question { 17263 }

why we use MV panels???
what's r all the needs

Answer

MV panel used to distribute the power to the relevant
panels. Which consist of metering, phase displaying,
protection relays,breakers, counters etc.

ersaravananp@gmail.com
saravanan.P

Is This Answer Correct ?

12 Yes

0 No

Question { Adani, 9455 }

what is power factor?

Answer

A graph drawn between voltage(V) and Current(I), a curve
will form due to loss between voltage and current. This is
called power factor.

This is also defind as the ratio between Apparent power to
Actual power.

Power Factor = KW / KVA.

Is This Answer Correct ?

9 Yes

2 No

Question { MahaGenco, 8177 }

working principle of generators?

Answer

According the Faraday's Law,Whenever current carrying
conductor cuts the magnetic field, dynamically EMF(Electro
Magmetic Force)is induced.This induced EMF produce the rate
of change of flex.

This will helps the rotate the generators.

Also, Generators operating as the principles of Fleming's
left hand rules.

Is This Answer Correct ?

3 Yes

9 No

Question { Adani, 6131 }

fundamentals of transformers.

Answer

The fundamentals of transformer is the transfer the energy
from one circuit to other circuit due to magnetic induction
between them without changing the frequency. Here no
movable parts. So losses are highly reduced.

Magnetic Induction (M) = L.dt/dI.

Is This Answer Correct ?

1 Yes

3 No

Question { 6569 }

how many types erthig

Answer

According to the connection, 2 types of earthings are there.
1. Body earthing - The earth connect to the body of motors,
transformers, generators.
2. Neutral earthing - The earth connect to the neutral
points of supply.

Is This Answer Correct ?

2 Yes

5 No

Question { 5979 }

in an industrical wiring, why we are using lighting DB and
Power DB separately?

Answer

In an industries, they are using different load. If we are
using single DB for lighting and power means, the variation
of load when we are using will affect the input voltage.

The lighting load is the uniform load and small. But the
power load will varry according the usage. For better
maintanence both DB's are provide separately and providing
the separate size of input cables.

Is This Answer Correct ?

10 Yes

0 No

Question { ABB, 21633 }

what is use of capacitor in fan

Answer

Due to single phase, the fan will not rotate. The capacitor
is having leading power factor.That is +90 degree leading
from phase voltage.

Due to capacitor, The single phase splits into two phases.
This phase difference use to stimulate the fan to rotate.

Is This Answer Correct ?

117 Yes

10 No

Question { wbsedcl, 13176 }

If DC supply is given to a transformer it may
a) Work
b)Not Work
c)Give lower voltage than the rated voltage on secondary
side.
d)burn the winding

Answer

The Transformer is working based on the principle of mutual
induction(M) between primary and secondary winding.
(M = L. dt/dI). This induction comes due to the magnetic
flex produced by AC supply.

In DC, No meaning of flex. So induction between two
windings is not possible. thus when we are giving DC supply
to Primary winding, It act as a normal conductor.

Due to copper loss of the winding, the heat will increases
and this will affect the winding including insulation
strength.

Is This Answer Correct ?

35 Yes

1 No

Question { 24458 }

how many voltage or current enough to kill a person?

Answer

1) In AC,
Voltage = 230 Volts.
Current = 5 Amps.
2) In DC,
Voltage = 50 Volts,
Current = 5 Amps. enough to kill a person.

And also, it is depends on the time duration. Minimum 5 Sec
required to kill a person.

Is This Answer Correct ?

3 Yes

20 No

Question { Power Grid, 67806 }

11kv has three live wires how much voltage is in its single
wire(leaving the other two wires)

Answer

In 3 phase 3 wire systems, The line voltage(three wire) is
1.732 (Route 3) times of the Phase voltage (Single wire).

hence line voltage (three wire) = 11 KV.
so phase voltage(single wire) = 11/1.732 KV.
= 6.35 KV.

Is This Answer Correct ?

175 Yes

22 No

Question { 6428 }

how electrical energy is converted into mechanical energy in
dc motor

Answer

In DC motor, The stator and rotor are calles as the
armature and field.

The armature is a rotation part and field is a coil (like
inductive coil).

If we are giving DC to field coil, The coil act as a
temporary magnet. The magnetic field passed to the armature
winding through induction. The flex difference between
armature and field will stimulate the armature to rotate.

This is the way the electrical energy converted into
mechanical energy in DC motor.

Is This Answer Correct ?

0 Yes

2 No

Question { 6725 }

What happened when we give 2 phase supply to a 1 phase
equimpent. It's effect on equipment's efficiency and life?

Answer

Two phase is nothing but two single phase. The single phase
supply have 230V AC. If you are provide two single phase in
a two terminal of single phase machine means, the potential
difference(Voltage) will occur. Current will pass through
it.It will act as a series circuit.

In series circuit, the total current(I) is equal to sum of
two individual currents(I1+I2). So the current value will
increase (almost double of the single phase current).

The increase of current will increase the temporature. This
will damage the minute or weak part of the equipments. So
life time, strength and quality of equipment will damaged.

by
ersaravananp@gmail.com

Is This Answer Correct ?

2 Yes

1 No

Question { 27472 }

What is the main function of fuse?

Answer

The main function of fuse is to avoid the fault current or
short circuit current enter through the healthy circuit.
This is used to isolate the entire circuit from fault one.

Is This Answer Correct ?

78 Yes

6 No

Question { 16471 }

Why inverter rating in KVA?

Answer

The inverter rating is in KVA because of in any active
components (like transformers, D.G, inverters etc..), the
power is calculating based on the output of the devices. At
the output terminals, no losses are considered causing by
active/passive loads (R,L,C). This is not depend on the
input.

But in the passive components (like motors, engine etc..),
the output is taking by means of input.

The output is always lesser than the input due to losses.
So the motors are denoted in the unit of KW.

Is This Answer Correct ?

6 Yes

8 No