Slip ring Induction Motors
The construction of the slip ring induction motor is exactly similar to the construction of squirrel cage induction motor. There is no difference between squirrel cage and slip ring motors.
The rotor of the slip ring induction motor is also cylindrical or constructed of lamination.
Squirrel cage motors have a rotor with short circuited bars whereas slip ring motors have wound rotors having "three windings" each connected in star.
The winding is made of copper wire. The terminals of the rotor windings of the slip ring motors are brought out through slip rings which are in contact with stationary brushes as shown in Fig: 3.2.
• It has susceptibility to speed control by regulating rotor resistance.
• High starting torque of 200 to 250% of full load value.
• Low starting current of the order of 250 to 350% of the full load current.
Hence slip ring motors are used where one or more of the above requirements are to be met.