Question

In a 4 pole induction motor, the rotor speed is 1400 rpm. What will be the air gap field speed?
1. 1400 rpm
2. 1700 rpm
3. 1600 rpm
4. 1500 rpm

Answer 1

Correct Answer - Option 4 : 1500 rpm

Concept:

• In a three-phase induction motor, a stator is stationary and a rotor is a rotating part.
• Both stator field and rotor field rotates with synchronous speed.
• The rotor rotates with a speed less than synchronous speed.
• The relative speed between rotor field and a stator is synchronous speed.

 

Application:

Rotor speed = 1400 rpm

Air gap field speed is the synchronous speed.

Therefore, the speed must be close to the 1400 rpm i.e. 1500 rpm.