SOLUTION

A wound rotor induction motor is preferred over a squirrel cage induction motor when the major consideration involved is High starting Torque, Low starting current & Speed control over the limited range.

The wound-rotor induction motor is also called a slip ring induction motor. The energy is collected through the slip rings connected to the rotor shaft the squirrel cage motors have copper end rings under the brush from where the short-circuited current can be collected.

Advantages of slip ring Induction motor

• It is possible to get high starting torque by the introduction of resistance in the rotor circuit.
• Starting current is comparatively less and it is 2 to 25 times full-load current or even less if required.
• It is capable of starting with load, demanding a high torque, as in fans, pumps, compass, boils, conveyors, cranes, lifts, and so on.
• Speed control is possible by varying the resistance in the external circuit of the rotor.
• The motor can be started direct-on-line (DOL) without the necessity of starters, because of the low starting current of the motor.

Disadvantages of slip ring Induction motor

• Higher cost
• Slightly Lower efficiency than squirrel cage induction motor
• Losses by the heat dissipation in external resistance especially when the motor runs at reduced speeds the below-rated speed.
• Require higher degree of maintenance