Polyphase Induction Motors Mcqs

This set of Electrical engineering Multiple Choice Questions & Answers (MCQs) focuses on “Polyphase Induction Motors”. These questions are chosen from a collection of most authoritative and best reference books on Electrical engineering. Our aim is to prepare an individual for competitive exams like NTS, GAT, ECAT, University and College entrance exams, Jobs and interviews. One should practice our MCQS to assimilate Polyphase Induction Motors Mcqs comprehensively.

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16.
The low power factor of induction motor is due to___________?

Rotor leakage reactance

Stator reactance

The reactive lagging magnetizing current necessary to generate the magnetic flux

All of the above

17.
In induction motor, percentage slip depends on__________?

Supply frequency

Supply voltage

Copper losses in motor

None of the above

18.
When /?2 is the rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running conditions will be_____________?

SR2X2 = 1

SR2 = X2

R2 = sX2

R2 = s2X2

19.
In case of a double cage induction motor, the inner cage has__________?

High inductance arid low resistance

Low inductance and high resistance

Low inductance and low resistance

High inductance and high resistance

20.
In an induction motor if air-gap is increased__________?

The power factor will be low

Windage losses will be more

Bearing friction will reduce

Copper loss will reduce In an induction motor

21.
The torque developed by a 3-phase induction motor least depends on__________?

Rotor current

Rotor power factor

Rotor e.m.f.

Shaft diameter

22.
Which motor is preferred for use in mines where explosive gases exist ?

Air motor

Induction motor

D.C. shunt motor

Synchronous motor

24.
The circle diagram for an induction motor cannot be used to determine____________?

Efficiency

Power factor

Frequency

Output

25.
Blocked rotor test on induction motors is used to find out?

Leakage reactance

Power factor on short circuit

Short-circuit current under rated voltage

All of the above

26.
The complete circle diagram of induetion motor can be drawn with the help of data found from__________?

Noload test

Blocked rotor test

Stator resistance test

All of the above

27.
In the squirrel-cage induction motor the rotor slots are usually given slight skew__________?

To reduce the magnetic hum and locking tendency of the rotor

To increase the tensile strength of the rotor bars

To ensure easy fabrication

None of the above

28.
The torque of a rotor in an induction motor under running condition is maximum__________?

At the unit value of slip

At the zero value of slip

At the value of the slip which makes rotor reactance per phase equal to the resistance per phase

At the value of the slip which makes the rotor reactance half of the rotor

29.
What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero ?

The slip of the motor will be 5%

The rotor will not run

The rotor will run at very high speed

The torque produced will be very large

30.
The stating torque of the slip ring induction motor can be increased by adding__________?

External inductance to the rotor

External resistance to the rotor

External capacitance to the rotor

Both resistance and inductance to rotor

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