1. What is the disadvantage of starting an induction motor with a star-delta starter ?

The starting torque is one third of the torque in case of the delta connection

During starting high losses are produced

The starting torque increases and the motor runs with jerks

None of the above

Answer: The starting torque is one third of the torque in case of the delta connection

Explanation:


2. In a 3-phase induction motor, iron loss ?

ln rotor is negligible as compared to that in stator

in stator does not occur

in rotor is equal to iron loss is stator

in rotor is much more than the iron loss in stator

Answer: ln rotor is negligible as compared to that in stator

Explanation:


3. Phase advancers are used with induction motors to ?

reduce noise

reduce vibrations

reduce copper losses

improve power factor

Answer: improve power factor

Explanation:


4. The purpose of using short-circuit gear is ?

to short circuit the rotor at slip rings

to short circuit the starting resistances in the starter

to short circuit the stator phase of motor to form star

none of the above

Answer: to short circuit the rotor at slip rings

Explanation:


5. Insertion of resistance in the stator of an induction motor ?

increases the load torque

decreases the starting torque

increases the starting torque

none of the above

Answer: decreases the starting torque

Explanation:


6. A change of 4% of supply voltage to an induction motor will produce a change of approximately ?

4% in the rotor torque

8% in the rotor torque

12% in the rotor torque

16% in the rotor torque

Answer: 16% in the rotor torque

Explanation:


7. The stating torque of the slip ring induction motor can be increased by adding ?

external inductance to the rotor

external resistance to the rotor

external capacitance to the rotor

both resistance and inductance to rotor

Answer: external resistance to the rotor

Explanation:


8. The maximum torque in an induction motor depends on ?

frequency

rotor inductive reactance

square of supply voltage

all of the above

Answer: all of the above

Explanation:


9. The term 'cogging' is associated with ?

three phase transformers

compound generators

DC. series motors

induction motors

Answer: induction motors

Explanation:


10. The frame of an induction motor is usually made of ?

silicon steel

cast iron

aluminium

bronze

Answer: cast iron

Explanation: