Design of Three Phase Induction Motor MCQ PDF

1. Output coefficient of induction motor is given as

(a) output/active volume of machine
(b) active volume of machine /output
(c) output/input
(d) input/output

2. If the stator winding of a 3-phase induction motor is delta connected, the rotor winding

(a) should be delta connected.
(b) should be star connected.
(c) should not be delta connected.
(d) may be delta or star connected.

3. A 3-phase squirrel cage induction motor designed to operate with stator in star, needs W kg of copper for its stator winding. Now if this motor is to be designed to operate with stator in delta, then weight of copper required for stator would be

(a) √3 W kg
(b) W/√3 kg
(c) 3W kg
(d) W/3 kg

4. An increase in number of poles of an induction motor results in

(a) decrease in maximum pf.
(b) increase in maximum pf.
(c) no change in maximum pf.
(d) cannot be predicted.

5. The effect of leakage flux in case of 3-phase induction motor is to

(a) reduce the torque produced.
(b) increase the torque produced.
(c) increase the operating power factor.
(d) none of the above.

6. ……….depends on leakage reactance in an induction motor.

(a) Starting current
(b) Starting torque
(c) Maximum torque
(d) All of the above

7. In an induction motor, leakage reactance is due to……….leakage flux.

(a) slot
(b) overhang
(c) differential
(d) all of these

8. Leakage reactance per phase, of the stator of a poly-phase, induction motor is 1.0 ohm. The turns per phase of the stator are increased by 10%. The leakage reactance is then equal to

(a) (1.1)²
(b) (0.9)²
(c) 1/(1.1)²
(d) 1/(0.9)²

9. When a 3-phase induction motor is designed with higher value of B_av it will give

(a) better full-load power factor.
(b) a higher starting torque.
(c) higher full load efficiency.
(d) higher overload capacity.

10. A machine with large value of specific magnetic loading has

(a) poor power factor.
(b) poor efficiency.
(c) poor maximum power output and poor overload capacity.
(d) less iron-losses.
(e) both (a) and (b).

11. In case of induction motors, the air-gap flux density usually taken is

(a) 0.1 to 0.2 T.
(b) 0.2 to 0.35 T.
(c) 0.3 to 0.6 T.
(d) 1.0 to 1.5 T.

12. Higher values of flux density can be taken while designing machines for

(a) larger rotor diameter.
(b) larger output.
(c) both (a) and (b).
(d) none of these.

13. Higher values of flux density can be taken while designing machines for

(a) smaller number of poles.
(b) low voltages.
(c) both (a) and (b).
(d) none of these.

14. In an induction motor, specific electric loading is not governed by

(a) commutation.
(b) temperature rise.
(c) overload capacity.
(d) voltage.
(e) machine size.

15. In induction motor, higher values of ampere-conductors give rise to

(a) increased copper losses leading to increased temperature rise and poor efficiency.
(b) increase in overload capacity.
(c) decrease in size of motor.
(d) all of the above.

16. High voltage induction motors have number of ampere-conductors.

(a) large
(b) small
(c) very large

17. The average value of ampere-conductors for induction motors is in the range of ampere-conductors per metre

(a) 50 to 100
(b) 20,000 to 50,000
(c) 5,000 to 45,000
(d) 50,000 to 1,00,000

18. With larger values of L/t, the insulation cost

(a) increases.
(b) decreases.
(c) remains unaffected.
(d) none of these.

19. For good overall design of induction motors, the ratio of L/t for a fixed number of poles should be

(a) 1.2 to 2
(b) 1.5
(c) 1.0
(d) 1.0 to 1.25

20. In general, the value of L/t lies between………..depending on the size of the machine and characteristics desired.

(a) 0.6 and 2
(b) 1.0 to 1.25
(c) 1.2 to 2
(d) 0.5 to 2.5