Question

The induction motor rotor design that can connect to external resistance using slip rings is: Select one: 1. Cage rotor 2. Synchronous rotor 3. Wound rotor 4. Polyphase rotor

Answer 1

Answer is option 3. Wound rotor

This is also called as slip ring induction motor. In this motor the rotor winding is provided with terminals open , so that external resistance can be added or can be short circuited externally. For starting the wound rotor motor we add resistance to the rotor and later short circuit it after catching a good speed.By adding the resistance to the rotor we can achieve good starting torque.

Looking at Other options:

In the Cage rotor type induction motor , the rotor is short circuited and the methods like -capacitor starting is employed.

Synchronous rotor and poly phase rotor are also short circuited internally.