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Electrical Engineering Objective Questions { Induction Motors }



8. 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

9. For starting a Schrage motor, 34 supply is connected to
A. stator as in an ordinary induction motor
B. rotor via slip-rings
C. regulating winding
D. secondary winding via brushes

10. When a Schrage motor runs exactly at synchronous speed, then
A. it behaves, in a sense, like a synchronous motor with compensating winding functioning as dc exciter
B. the speed of the motor field relative to that of the regulating winding becomes zero
C. secondary voltage E2 comes into phase with primary back emf. El.
D. voltage injected from compensating winding into secondary becomes equal and opposite to the secondary induced voltage.

11. In some induction motors, copper bars are placed deep in the rotor. It is done so that
A. slip under normal running conditions is reduced
B. p.f. is improve
C. starting torque is increased
D. output is increased

12. The fractional slip of an induction motor is the ratio
A. rotor Cu loss/rotor input
B. stator Cu loss/stator input
C. rotor Cu loss/rotor output
D. rotor Cu loss/stator Cu loss

13. The principle of operation of a 3-phase induction motor is most similar t that of a
A. synchronous motor
B. repulsion-start induction motor
C. transformer with a shorted secondary
D. capacitor-start, induction-run motor

14. Which method is the least used for 3-phase motor starting?
A. Y-6,
B. auto-transformer
C. across-the-line
D. primary resistors

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