How does a wound-rotor induction motor differ from a squirrel-cage induction motor?

The primary difference between these two types of induction motors lies in their rotor construction and the resulting control capabilities.

Squirrel-Cage Induction Motors

In most induction motors, the rotor features a squirrel-cage design. This consists of solid conductors (typically aluminum or copper bars) shorted together at both ends by conducting rings. Because these conductors do not require electrical insulation from the rotor iron, the design is exceptionally rugged and economical to manufacture.1

Wound-Rotor Induction Motors

Conversely, a wound-rotor motor is constructed with insulated polyphase windings in the rotor, similar to those found in the stator. These windings connect to external circuits via slip rings and carbon brushes. This configuration allows for:2
* High Starting Torque: By connecting external resistors to the slip rings, the motor can achieve high starting torque without drawing excessive current.2
* Speed Control: Varying the external resistance allows for a degree of speed regulation, though this can be inefficient unless operating near synchronous speed.2

While the squirrel-cage motor is favored for its simplicity and durability, the wound-rotor motor provides secondary circuit adjustments that are not possible with the squirrel-cage design.3