Question

a) What is the advantages of using a wound-rotor type of induction motor? Under what conditions?

b) When starting a wound rotor induction motor, what is the supposed value of resistance of the slip-ring starter?

c) What is the wound rotor method of speed control?

Answer 1

Wound rotor Motor also known as slip ring induction motor which have external slip rings to connect the external resistance at rotor side .

Slip ring induction motor has hight starting torque and low starting current.

Low starting current is due to at the time of starting we intentionally connect the external resistance at rotor side to bring down the starting current. These are the main advantages for the wound rotor induction motor.

2) at the time of starting induced emf is more in rotor side if rotor resistance is less at starting the chance of rotor winding burn due to higher current. To limit the current we add more resistance at rotor side through the slip rings.

3) slip of motor at maximum torque is equal to( R2+Text)/X2

By controlling the externt resistance we can control the slip at maximum torque so there by we get different speeds at different external resistance values at slip ring terminals.

For different slip values we get different speeds but maximum torque is same , in this way we control the speed of slip ring induction motor through varying the resistance at slip rings.