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Polyphase Induction Motors

Study 99 Electrical Engineering MCQs with correct answers and explanations.

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11Electrical EngineeringMedium

For which motor the speed can be controlled from rotor side?

ASlip-ring induction motor

BBoth A. and (b)

CNone of the above

DSquirrel-cage induction motor

Correct answer

A. Slip-ring induction motor

Explanation

The correct answer is Slip-ring induction motor.

12Electrical EngineeringMedium

The circle diagram for an induction motor cannot be used to determine________?

Aefficiency

Bpower factor

Coutput

Dfrequency

Correct answer

A. efficiency

Explanation

The correct answer is efficiency.

13Electrical EngineeringMedium

In medium sized induction motors, the slip is generally around________?

A0.4%

B4%

C14%

D0.04%

Correct answer

B. 4%

Explanation

The correct answer is 4%.

14Electrical EngineeringMedium

The starting torque of a 3-phase squirrel cage induction motor is________?

A1.5 times the full load torque

Btwice the full load torque

Cequal to full load torque

Correct answer

A. 1.5 times the full load torque

Explanation

The correct answer is 1.5 times the full load torque.

15Electrical EngineeringMedium

Which of the following component is usually fabricated out of silicon steel?

AShaft

BBearings

CStatorcore

DNone of the above

Correct answer

C. Statorcore

Explanation

The correct answer is Statorcore.

16Electrical EngineeringMedium

If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as________?

Acrawling

Bcogging

Chunting

Dhumming

Correct answer

A. crawling

Explanation

The correct answer is crawling.

17Electrical EngineeringMedium

In case the air gap in an induction motor is increased________?

Athe windage losses will increase

Bthe magnetising current of the rotor will decrease

Cspeed of motor will increase

Dthe power factor will decrease

Correct answer

D. the power factor will decrease

Explanation

The correct answer is the power factor will decrease.

18Electrical EngineeringMedium

Slip of an induction motor is negative when________?

Anone of the above

Brotor speed is more than the synchronous speed of the field and are in the same direction

Crotor speed is less than the synchronous speed of the field and are in the same direction

Dmagnetic field and rotor rotate in opposite direction

Correct answer

B. rotor speed is more than the synchronous speed of the field and are in the same direction

Explanation

The correct answer is rotor speed is more than the synchronous speed of the field and are in the same direction.

19Electrical EngineeringMedium

The torque of an induction motor is________?

Aproportional to the square of the slip

Bdirectly proportional to slip

Cnone of the above

Dinversely proportional to slip

Correct answer

B. directly proportional to slip

Explanation

The correct answer is directly proportional to slip.

20Electrical EngineeringMedium

In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be________?

ANs

B(Ns-l)s

C(l-s)Ns

Ds.N,

Correct answer

C. (l-s)Ns

Explanation

The correct answer is (l-s)Ns.

Slip of an induction motor is negative when________?

Anone of the above

Brotor speed is more than the synchronous speed of the field and are in the same direction

Crotor speed is less than the synchronous speed of the field and are in the same direction

Dmagnetic field and rotor rotate in opposite direction

Correct answer

B. rotor speed is more than the synchronous speed of the field and are in the same direction

Explanation

The correct answer is rotor speed is more than the synchronous speed of the field and are in the same direction.