3-phase induction motors. Part – 1

1. In induction motor Ns is the synchronous speed and S slip, then actual running speed of an induction motor will be

A. Ns

B. S∙Ns

C. (1-S)Ns

D. (Ns-1)S

2. The torque developed in an induction motor is nearly proportional to

A. 1/V

B. V

C. V²

D. 1/V²

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

A. The magnetizing current of the rotor is increased

B. The power factor will decrease

C. Speed of motor will increase

D. The winding losses will increase

4. The crawling in an induction motor is caused by

A. High loads

B. Improve design of machine

C. Low voltage supply

D. Harmonics developed in the motor

5. In order to achieve good power factor of an induction motor, the average flux density in air gap should be,

A. small

B. large

C. infinity

D. more than 1.5 Wb/m²

6. What are the expectation from an ideal motor starter?

A. Limitation of starting current

B. Improvement of starting torque

C. Smooth starting of motor

D. All of the above

7. In case of induction motors, the full load slip is generally,

A. 0.3 to 0.5%

B. 20 to 50%

C. 30 to 50%

D. 3 to 5%

8. The slip speed of an induction motor depends upon

A. Armature current

B. Eddy currents

C. Core losses

D. Mechanical load

9. In squirrel cage induction motor, the rotor slots are usually given slight skew in order to

A. Reduce magnetic hum

B. Reduce accumulation of dirt and dust

C. Reduce eddy currents

D. Reduce windage losses

10.  A 3–phase 6-pole 50Hz induction motor is running at 5% slip, what will be the speed of motor?

A. 850 rpm

B. 950 rpm

C. 900 rpm

D. 1000 rpm