Unit -2

Three Phase Induction Motors

Question

1. Derive the expression for the different torque ratios of 3-ph induction motor.
2. Explain with neat labeled sketch

i) torque- slip characteristic of an induction motor

Ii) effect of rotor resistance on torque- slip characteristic.

3.     A 3-ph induction motor having a 6 poles, star- connection stator winding runs on 240V, 50 Hz supply. The rotor impedance per phase at standstill is (0.12+j 0.85)Ω. The ratio of stator to rotor turns is 1.8. Full load slip is 4%.

Calculate:

i)                   Full – load torque

Ii)                ii) maximum torque

Iii)             iii) speed at maximum torque

4.     Derive the expression for the torque of a 3-ph induction motor and obtain condition for maximum torque. What is the expression for the maximum torque?

5.     Draw and explain the different types of starters

6.     Explain the different power stages in an induction motor.

7.     Give any four applications of induction motor.

8.     Explain speed control methods of an induction motor.