[Set3]AE KSEB Interview Questions|Basic Electrical Engineering Interview Questions

Electrical Engineering Interview Questions : These questions are useful for Assistant Engineer Electrical KSEB, Sub Enginner Electrical and other electrical Exams.

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Electrical Engineering Interview Questions

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Why series motor cannot be started on no-load?

Answer: Series motor cannot be started without load because of high starting torque. Series
motor are used in Trains, Crane etc.

Why ELCB can’t work if N input of ELCB do not connect to ground?

Answer: ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in
an ELCB, the current will flow through phase and that much current will have to return neutral so
resultant current is zero. Once there is a ground fault in the load side, current from phase will
directly pass through earth and it will not return through neutral through ELCB. That means once
side current is going and not returning and hence because of this difference in current ELCB will
trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded, fault
current will definitely high and that full fault current will come back through ELCB, and there will
be no difference in current.

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How electrical power is generated by AC generator?

Answer: For the generation of elect power we need a prime mover which supplies mechanical
power input to the alternator, can be steam turbines, or hydro turbines. When the poles of the rotor
moves under the armature conductors which are placed on the stator ,field flux cut the armature
conductor ,therefore voltage is generated and is of sinusoidal in nature…due to polarity change
of rotor poles(i,e) N-S-N-S.

Why an ac solenoid valve attract the plunger even though we interchanges the terminal? Will the poles changes?

Answer: Yes because the poles changes for every half-cycle of ac voltage so the polarity of AC
voltage is continuously changing for every half cycle. So, interchanging of terminals in ac system
does not show any difference. That’s why the ac solenoid attract the plunger even though its
terminals are interchanged.

What is derating? Why it is necessary, it is same for all means for drives, motors, and cables.

What is Automatic Voltage regulator (AVR)?

Answer: AVR is an abbreviation for Automatic Voltage Regulator. It is important part in
Synchronous Generators, it controls the output voltage of the generator by controlling its
excitation current. Thus it can control the output Reactive Power of the Generator.

What is an exciter and how does it work?

Answer: There are two types of exciters, static exciter and rotary exciter. Purpose of exciter is to
supply the excitation dc voltage to the fixed poles of generator. Rotary exciter is an additional
small generator mounted on the shaft of main generator. If it is dc generator, it will supply dc to
the rotary poles through slip ring and brushes (conventional alternator). if it is an ac exciter,
output of ac exciter is rectified by rotating diodes and supply dc to main fixed poles.ac exciter is
the ac generator whose field winding are stationary and armature rotates. Initial voltage is built
up by residual magnetism. It gives the starting torque to the generator.

Difference between a four point starter and three point starter?

Answer: The shunt connection in four point stater is provided separately from the line where as
in three point stater it is connected with line which is the drawback in three point stater

Why use the VCB at High Transmission System? Why can’t use ACB?

Answer: Actually the thing is vacuum has high arc quenching property compare to air because in
VCB, the die electric strengths equal to 8 times of air. That y always vacuum used as in HT
breaker and air used as in LT.

What is the difference between surge arrestor and lightning arrestor?

Answer: LA is installed outside and the effect of lightning is grounded, whereas surge arrestor
installed inside panels comprising of resistors which consumes the energy and nullify the effect of
surge.

Why syn. generators r used for the production of electricity?

Answer: synchronous machines have capability to work on different power factor (or say
different imaginary POW varying the field emf. Hence syn. generators r used for the production
of electricity.

Enlist types of dc generator?

Answer: D.C. Generators are classified into two types
1) Separately excited d.c.generator
2) Self-excited d.c.generator, which is further classified into; 1) series 2) shunt and
3) Compound (which is further classified into cumulative and differential).

What is the difference between synchronous generator & asynchronous generator?

Answer: In simple, synchronous generator supply’s both active and reactive power but
asynchronous generator (induction generator) supply’s only active power and observe reactive
power for magnetizing. This type of generators are used in windmills.

Give two basic speed control scheme of DC shunt motor?

Answer:

1. By using flux control method: in this method a rheostat is connected across the field
winding to control the field current.so by changing the current the flux produced by the field
winding can be changed, and since speed is inversely proportional to flux speed can be
controlled

2.Armature control method: in this method a rheostat is connected across armature winding by
varying the resistance the value of resistive drop (IaRa) can be varied, and since speed is directly
proportional to Eb-IaRa the speed can be controlled.