### Polyphase Induction Motors

1. Insertion of resistance in the stator of an induction motor

2. decreases the starting torque
3. increases the starting torque
4. none of the above

decreases the starting torque

2. The starting torque of a three phase induction motor can be increased by

1. increasing slip
2. increasing current
3. both (a) and (b)
4. none of the above

both (a) and (b)

3. 5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m. Which motor will be the costliest?

1. 730 r.p.m.
2. 960 r.p.m.
3. 1440 r.p.m.
4. 2880 r.p.m.

730 r.p.m.

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

1. 200 Hz
2. 50 Hz
3. 2 Hz
4. 0.2 Hz

2 Hz

5. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor

1. will continue running burning its one phase
2. will continue running burning its two phase
3. will stop and carry heavy current causing permanent damage to its winding
4. will continue running without any harm to the winding

will stop and carry heavy current causing permanent damage to its winding

6. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor

1. will continue running burning its one phase
2. will continue running burning its two phases
3. will stop and carry heavy current causing permanent damage to its winding
4. will continue running without any harm to the winding

will continue running burning its one phase

7. A 3-phase slip ring motor has

1. double cage rotor
2. wound rotor
3. short-circuited rotor
4. any of the above

wound rotor

8. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6 poles. The slip of the machine will be

1. 0.01
2. 0.02
3. 0.03
4. 0.04

0.04

9. A change of 4% of supply voltage to an induction motor will produce a change of appromimately

1. 4% in the rotor torque
2. 8% in the rotor torque
3. 12% in the rotor torque
4. 16% in the rotor torque