1. The principle of operation of a 3-phase induction motor is most similar to that of ?

transformer with a shorted secondary

synchronous motor

capacitor-start induction run motor

repulsion-start induction motor

Answer: transformer with a shorted secondary

Explanation:


2. In a squirrel cage motor the induced e.m.f. is ?

dependent on the shaft loading

dependent on the number of slots

slip times the stand still e.m.f. induced in the rotor

none of the above

Answer: slip times the stand still e.m.f. induced in the rotor

Explanation:


3. Insertion of resistance in the rotor of an induction motor to develop a given torque ?

decreases the rotor current

increases the rotor current

rotor current becomes zero

If rotor current remains same

Answer: If rotor current remains same

Explanation:


4. The power factor of an induction motor under no-load conditions will be closer to ?

0.2 lagging

0.2 leading

0.5 leading

unity

Answer: 0.2 lagging

Explanation:


5. When the equivalent circuit diagram of double squirrel-cage induction motor is constructed the two cages can be considered ?

in series

in parallel

in series-parallel

in parallel with stator

Answer: in parallel

Explanation:


6. The number of slip rings on a squirrel cage induction motor is usually ?

two

three

four

none

Answer: none

Explanation:


7. In an induction motor, no-load the slip is generally ?

less than 1%

1.6%

2%

4%

Answer: less than 1%

Explanation:


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

will continue running burning its one phase

will continue running burning its two phase

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

will continue running without any harm to the winding

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

Explanation:


9. Which type of bearing is provided in small induction motors to support the rotor shaft ?

Ball bearings

Cast iron bearings

Bush bearings

None of the above

Answer: Ball bearings

Explanation:


10. When a stationary 3-phase induction motor is switched on with one phase disconnected ?

it will start but run very slowly

it will make jerky start with loud growling noise

remaining intact fuses will be blown out due to heavy rush of current

it is likely to burn out quickly unless immediately disconnected

Answer: it is likely to burn out quickly unless immediately disconnected

Explanation: