3 Phase Induction Motor Multiple Choice Questions And Answers In English -01

3 Phase Induction Motor Multiple Choice Questions And Answers In English 
1. Which of the following component is usually fabricated out of silicon steel ?

(1) Bearings
(2) Shaft
(3) Stator Core
(4) None of the above
Ans: (3)

2. The frame of an induction motor is usually made of
(1) silicon steel
(2) cast iron
(3) aluminium
(4) bronze
Ans: (2)

3. In medium sized induction motors, the slip is generally around
(1) 0.04%
(2) 0.4%
(3) 4%
(4) 14%
Ans: (3)

4. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ?
(1) By changing the number of stator poles
(2) Rotor rheostat control
(3) By operating two motors in cascade
(4) By injecting e.m.f. in the rotor circuit
Ans: (1)

5. In case of the induction motors the torque is
(1) inversely proportional to (Vslip)
(2) directly proportional to (slip)2
(3) inversely proportional to slip
(4) directly proportional to slip
Ans: (4)

6. A double squirrel-cage induction motor has
(1) two rotors moving in oppsite direction
(2) two parallel windings in stator
(3) two parallel windings in rotor
(4) two series windings in stator
Ans: (3)

7. When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be
considered
(1) in series
(2) in parallel
(3) in series-parallel
(4) in parallel with stator
Ans: (2)

8. Stepless speed control of induction motor is possible by which of the following methods ?
(1) E.M.F.  injection in rotor circuit
(2) Changing the number of poles
(3) Cascade operation
(4) None of the above
Ans: (2)

9. The maximum torque in an induction motor depends on
(1) frequency
(2) rotor inductive reactance
(3) square of supply voltage
(4) all of the above
Ans: (4)

10. The shaft of an induction motor is made of
(1) stiff
(2) flexible
(3) hollow
(4) any of the above
Ans: (1)

11. The injected e.m.f. in the rotor of induction motor must have

(1) zero frequency
(2) the same frequency as the slip frequency
(3) the same phase as the rotor e.m.f.
(4) high value for the satisfactory speed control
Ans: (2)

12. The crawling in the induction motor is caused by
(1) low voltage supply
(2) high loads
(3) harmonics developed in the motor
(4) improper design of the machine
Ans: (3)

13. The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type
(1) star connected only
(2) delta connected only
(3) (1) and (2) both
(4) none of the above
Ans: (3)

14. The shaft of an induction motor is made of
(1) high speed steel
(2) stainless steel
(3) carbon steel
(4) cast iron
Ans: (3)

15. In the circle diagram for induction motor, the diameter of the circle represents
(1) slip
(2) rotor current
(3) running torque
(4) line voltage
Ans: (2)

16. For which motor the speed can be controlled from rotor side ?
(1) Squirrel-cage induction motor
(2) Slip-ring induction motor
(3) Both (1) and (2)
(4) None of the above
Ans: (2)

17. DOL starting of induction motors is usually restricted to
(1) low horsepower motors
(2) variable speed motors
(3) high horsepower motors
(4) high speed motors
Ans: (1)

18. The speed of a squirrel-cage induction motor can be controlled by all of the following except
(1) changing supply frequency
(2) changing number of poles
(3) changing winding resistance
(4) reducing supply voltage
Ans: (3)

19. Size of a high speed motor as compared to low speed motor for the same H.P. will be
(1) bigger
(2) smaller
(3) same
(4) any of the above
Ans: (2)

20. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor
(1) will continue running burning its one phase
(2) will continue running burning its two phases
(3) will stop and carry heavy current causing permanent damage to its winding
(4) will continue running without any harm to the winding
Ans: (1)