3-phase induction motors. Part – 2

11. In induction motor the air gap flux density is usually kept low so as to

A. Improve efficiency

B. Improve power factor

C. Reduce machine cost

D. None of the above

12. The medium size induction motor having maximum efficiency while operating at

A. 75% of full load

B. Half load

C. 25% of full load

D. Any load

13. The frequency of rotor current at standstill is equal to

A. Zero

B. 2f

C. f.

D. Sf.

14. A slip-ring induction motor is recommended for applications requiring

A. High starting torque

B. Variable speed operation

C. Frequent starting, stopping and reversing operations

D. All of the above features

15. The maximum torque in an induction motor depends to

A. Frequency

B. Rotor inductive reactance

C. Square of supply voltage

D. All of the above

16. Rotor of an induction motor runs at

A. Synchronous speed

B. Below synchronous speed

C. Above synchronous speed

D. Any of the above

17. 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

18. Slip ring induction motors are employed only for

A. Speed control

B. High starting torque

C. Both (A) and (B)

D. None of these

19. A motor having a power factor of 0.8 absorbs in active power of 1200W the reactive power drawn from the supply is ______ VAR.

A. 130

B. 900

C. 1500

D. 600

20. If V/f speed control of 3-phase induction motor, with increase in frequency, the slip at which maximum torque occurs

A. increase

B. decrease

C. either of these

D. none of the above