1. An induction motor is identical to
(a) D.C. compound motor
(b) D.C. series motor
(c) synchronous motor
(d) asynchronous motor
Ans: d
2. The injected e.m.f. in the rotor of induction motor must have
(a) zero frequency
(b) the same frequency as the slip fre-quency
(c) the same phase as the rotor e.m.f.
(d) high value for the satisfactory speed control
Ans: b
3. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ?
(a) By changing the number of stator poles
(b) Rotor rheostat control
(c) By operating two motors in cascade
(d) By injecting e.m.f. in the rotor circuit
Ans: a
4. The crawling in the induction motor is caused by
(a) low voltage supply
(b) high loads
(c) harmonics develped in the motor
(d) improper design of the machine
(e) none of the above
Ans: c
5. The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type
(a) star connected only
(b) delta connected only
(c) (a) and (b) both
(d) none of the above
Ans: c
6. The torque developed in the cage induction motor with autostarter is
(a) k/torque with direct switching
(6) K x torque with direct switching
(c) K2 x torque with direct switching
(d) k2/torque with direct switching
Ans: c
7. When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be
considered
(a) in series
(b) in parallel
(c) in series-parallel
(d) in parallel with stator
Ans: b
8. It is advisable to avoid line-starting of induction motor and use starter because
(a) motor takes five to seven times its full load current
(b) it will pick-up very high speed and may go out of step
(c) it will run in reverse direction
(d) starting torque is very high
Ans: a
9. Stepless speed control of induction motor is possible by which of the following methods ?
(a) e.m.f. injection in rotor eueuit
(b) Changing the number of poles
(c) Cascade operation
(d) None of the above
Ans: b
10. Rotor rheostat control method of speed control is used for
(a) squirrel-cage induction motors only
(b) slip ring induction motors only
(c) both (a) and (b)
(d) none of the above
Ans: b
11. In the circle diagram for induction motor, the diameter of the circle represents
(a) slip
(b) rotor current
(c) running torque
(d) line voltage
Ans: b
12. For which motor the speed can be controlled from rotor side ?
(a) Squirrel-cage induction motor
(b) Slip-ring induction motor
(c) Both (a) and (b)
(d) None of the above
Ans: b
13. If any two phases for an induction motor are interchanged
(a) the motor will run in reverse direction
(b) the motor will run at reduced speed
(c) the motor will not run
(d) the motor will burn
Ans: a
14. An induction motor is
(a) self-starting with zero torque
(b) self-starting with high torque
(c) self-starting with low torque
(d) non-self starting
Ans: c
15. The maximum torque in an induction motor depends on
(a) frequency
(b) rotor inductive reactance
(c) square of supply voltage
(d) all of the above
Ans: d
16. In three-phase squirrel-cage induction motors
(a) rotor conductor ends are short-circuited through slip rings
(b) rotor conductors are short-circuited through end rings
(c) rotor conductors are kept open
(d) rotor conductors are connected to insulation
Ans: b
17. In a three-phase induction motor, the number of poles in the rotor winding is always
(a) zero
(b) more than the number of poles in stator
(c) less than number of poles in stator
(d) equal to number of poles in stator
Ans: d
18. DOL starting of induction motors is usually restricted to
(a) low horsepower motors
(b) variable speed motors
(c) high horsepower motors
(d) high speed motors
Ans: a
19. The speed of a squirrel-cage induction motor can be controlled by all of the following except
(a) changing supply frequency
(b) changing number of poles
(c) changing winding resistance
(d) reducing supply voltage
Ans: c
20. The 'crawling" in an induction motor is caused by
(a) high loads
(6) low voltage supply
(c) improper design of machine
(d) harmonics developed in the motor
Ans: d
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