An AC motor in which torque is produced by the reaction between a varying magnetic field generated in the stator and the current induced in the coils of the rotor. There are two types of rotors in induction motor rotors, Squirrel-cage rotor, and slip ring rotor.
Squirrel cage rotor
- A squirrel-cage rotor is a rotating element that is used in a three-phase induction motor. It consists of a steel laminated bar with a cylinder with aluminum or copper conductors embedded in its surface.
- The function of bearings in a cage rotor motor is to reduce friction between the rotating and stationary parts of the machine. The rotor of the motor consists of a cylindrical laminated core with parallel slots for carrying the rotor conductors. The rotor conductors are no wires, but it consists of heavy bars of copper, aluminum, or an alloy. The shaft is used in the motor to transfer mechanical power from or to the machine. The stator is the outer stationary part of the motor.
Wound rotor or slip ring rotor
The wound rotor consists of a slotted armature. Insulated conductors are put in the slots and connected to form a three-phase double-layer distributed winding similar to the stator winding. The winding of the rotor is connected in star. Three-phase winding is placed at the rotor and stator. Open-end of the rotor connected to the insulated slip ring. Brushes are attached with the slip rings and are connected with external variable resistance.
The main function of the slip ring is to connect the resistance with rotor winding. External resistance is used for
- to reduce the starting current
- it is used to control the speed of the motor
- it is used to increase the starting torque.
- it is known as variable resistance because the position can be change
using external variable resistance, the speed of the motor can be controlled. Slip ring rotors have high starting torque.