Three Phase Wound Rotor Induction Motors
This motor is suited for starting highly inertial loads. A high starting resistance makes the high pull out torque available at zero speed. A shorted rotor operates like a squirrel cage rotor. The heat generated during starting is mostly dissipated external to the motor in the starting resistance.The complication and maintenance associated with brushes and slip rings is a disadvantage of the wound rotor as compared to the simple squirrel cage rotor. 
For comparison, a squirrel cage rotor only exhibits pull out (peak) torque at 80% of its synchronous speed.

Three Phase Wound Rotor Induction Motors