Polyphase Induction Motors MCQ - Electrician (Set-1) with Answers

Polyphase Induction Motors MCQ - Electrician (Set-1) with Answers

1) The synchronous speed of a 2, 4 and 8 poles motor at 50 Hz can not be

Answer is:

1000 R.P.M.

Explanation:

Speed of 2 Pole Motor
Ns=(120 x Frequency)/Number of Poles
Ns=(120×50)/2=3000 RPM

Speed of 4 Pole Motor
Ns=(120 x Frequency)/Number of Poles
Ns=(120×50)/4=1500 RPM

Speed of 8 Pole Motor
Ns=(120 x Frequency)/Number of Poles
Ns=(120×50)/8=750 RPM

2) The no. of poles of a 3-phase induction motor running at 500 R.P.M. will be : (supply frequency = 50 Hz)

Answer is:

12

3) The starting torque of a 3-phase induction motor can be increased :

Answer is:

by increasing the rotor resistance

4) At the time of starting, the slip of an induction-motor is equal to :

Answer is:

unit

5) The reason of drawing high current at the time of starting by an induction-motor is :

Answer is:

1) The synchronous speed of a 2, 4 and 8 poles motor at 50 Hz can not be

1000 R.P.M.

2) The no. of poles of a 3-phase induction motor running at 500 R.P.M. will be : (supply frequency = 50 Hz)

12

3) The starting torque of a 3-phase induction motor can be increased :

by increasing the rotor resistance

4) At the time of starting, the slip of an induction-motor is equal to :

unit

5) The reason of drawing high current at the time of starting by an induction-motor is :

zero back e.m.f.