3-PHASE INDUCTION MOTOR -1

1. The frame of an induction motor is usually made of ___________

silicon steel

cast iron

aluminium

bronze

2. The shaft of an induction motor is made of ____________

high speed steel

silicon steel

carbon steel

cast iron

3. In medium sized induction motors, the slip is generally around __________

0.04%

0.4%

14%

4. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to ____________

reduce windage loss

reduce eddy current loss

reduce accumulation of dirt and dust

reduce magnetic hum

5. In case the air gap in an induction motor is increased _____________

the magnetising current of the rotor will decrease

the power factor will decrease

speed of motor will increase

the windage losses will increase

6. Slip rings are usually made of ____________

copper

carbon

phosphor bronze

aluminium

7. A 3-phase 440V, 50Hz induction motor has 4% dlip. The frequency of rotor e.m.f. will be ____________

200 Hz

50 Hz

2 Hz

0.2 Hz

8. If Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be _____________

sNs

(1 - s)Ns

(Ns - 1)s

9. The efficiency of an induction motor can be expected to be nearly ___________

60 to 90%

80 to 90%

95 to 98%

99%

10. The number of slip rings on a squirrel cage induction motor is usually __________

none

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