3 Phase Induction Motors Objective Questions with Answers: Part-2

3 Phase Induction Motors Related ( MCQ ) Objective Questions with Answers

[1] Which of the following statements about a three-phase squirrel-cage induction motor are false?
(a) It has no external electrical connections to its rotor
(b) A three-phase supply is connected to its stator
(c) A magnetic flux which alternates is produced
(d) It is cheap, robust and requires little or no skilled maintenance

(1) A,B,C only
(2) C and D only
(3) C only
(4) None of the above
(5) B only

Ans: 3

[2] Which of the following statements about a three-phase induction motor are false?
(a) The speed of rotation of the magnetic field is called the synchronous speed
(b) A three-phase supply connected to the rotor produces a rotating magnetic field
(c) The rotating magnetic field has a constant speed and constant magnitude
(d) It is essentially a constant speed type machine

(1) C only
(2) B only
(3) A only
(4) All of the above
(5) A and C only

Ans: 2

well you can check this link (https://www.examcraze.in/government-jobs/ ) for more updates related to exams and more.

[3] Which of the following statements is false when referring to a three-phase induction motor?
(a) The synchronous speed is half the supply frequency when it has four poles
(b) In a 2-pole machine, the synchronous speed is equal to the supply frequency
(c) If the number of poles is increased, the synchronous speed is reduced
(d) The synchronous speed is inversely proportional to the number of poles

(1) All of the above
(2) D only
(3) B only
(4) None of the above
(5) A and C only

Ans: 2

[4] A 4-pole three-phase induction motor has a synchronous speed of 25 rev/s. The frequency of the supply to the stator is:
(a) 50 Hz
(b) 100 Hz
(c) 25 Hz
(d) 12.5 Hz

Ans: A

[5] In a three-phase induction motor. Which of the following statements are false?
(a) The slip speed is the synchronous speed minus the rotor speed
(b) As the rotor is loaded, the slip decreases
(c) The frequency of induced rotor e.m.f.�s increases with load on the rotor
(d) The torque on the rotor is due to the interaction of magnetic fields

(1) All of the above
(2) C only
(3) B only
(4) A and C only
(5) B and D only

Ans: 3

[6] In a three-phase induction motor. Which of the following statements are false?
(a) If the rotor is running at synchronous speed, there is no torque on the rotor
(b) If the number of poles on the stator is doubled, the synchronous speed is halved
(c) At no-load, the rotor speed is very nearly equal to the synchronous speed
(d) The direction of rotation of the rotor is opposite to the direction of rotation of the magnetic field to give maximum current induced in the rotor bars

(1) A, B , C
(2) C only
(3) B only
(4) A and C only
(5) D only

Ans: 5

[7] The slip speed of an induction motor may be defined as the:
(a) Number of pairs of poles � frequency
(b) Rotor speed - synchronous speed
(c) Rotor speed + synchronous speed
(d) Synchronous speed  - rotor speed

Ans:D

[8] The slip speed of an induction motor depends upon:
(a) Armature current
(b) Supply voltage
(c) Mechanical load
(d) Eddy currents

Ans: C

[9] The starting torque of a simple squirrel-cage motor is:
(a) Low
(b) Increases as rotor current rises
(c) Decreases as rotor current rises
(d) High

Ans: A

[10] The slip speed of an induction motor:
(a) is zero until the rotor moves and then rises slightly
(b) is 100 per cent until the rotor moves and then decreases slightly
(c) is 100 per cent until the rotor moves and then falls to a low value
(d) is zero until the rotor moves and then rises to 100 per cent

Ans: C

Please leave your comments below....

Read More »

Induction Motors Objective Questions: part 1

Solved Objective Questions from Induction Motors

[1] The crawling in an induction motor is caused by
(a) Improper design of the machine
(b) Low voltage supply
(c) High loads
(d) Harmonics developed in the motor

Ans: D

[2] The speed of an induction motor
(a) Decreases too much with the increase of load
(b) Increase with the increase of load
(c) Decreases slightly with the increase of load
(d) Remains constant with the increase of load

Ans: C

[3] The effect of increasing the length of the air gap in an induction motor will increase
(a) Power factor
(b) Speed
(c) Magnetising current
(d) Air-gap flux

Ans: C

[4] the difference between the synchronous speed and the actual speed of an induction motor is known as

(a) Regulation
(b) Back lash
(c) Slip
(d) Lag

Ans:C

[5] Rotating magnetic field is produced in a....
(a) Single - phase induction motor
(b) Three phase induction motor
(c) DC series motor
(d) AC series motor

Ans: B

[6] The stator core of the induction motor is made of
(a) Laminated cast iron
(b) Mild steel
(c) Silicon steel stampings
(d) Soft wood

Ans:C

[7] Star- delta starter of an induction motor
(a) Inserts resistance in rotor circuit
(b) Inserts resistance in stator circuit
(c) Applies reduced voltage to rotor
(d) Applies reduced voltage to stator

Ans: D

[8] The starting torque of a 1-phase induction motor is
(a) High
(b) Medium
(c) Low
(d) Zero

Ans: D

[9] The thrust developed by a linear induction motor depends on
(a) Synchronous speed
(b) Rotor input
(c) Number of poles
(d) Both A and B

Ans: D

[10] A 3-phase squirrel cage induction motor supplied from a balanced 3-phase source drives a mechanical load. The torque-speed characteristics of the motor (solid curve) and of the load (dotted curve) are shown. Of the two equilibrium points A and B, which of the following options correctly describes the stability of A and B? [GATE 2009]

(a) A is stable B is unstable

(b) A is unstable B is stable

(c) Both are stable

(d) Both are unstable

Ans: B

[11] If an induction machine is run at above synchronous speed, it acts as [Gate 1997]
(a) A synchronous motor
(b) An induction generator
(c) An induction motor
(d) None of the above

Ans: B

Thanks for reading....

Read More »