Which type of motor uses slip rings to connect rotor windings to the power supply?

The wound-rotor induction motor employs slip rings to connect the rotor windings to the external power supply. This design allows for torque control and smooth operation, especially beneficial in applications requiring high starting torque or variability in speed. In a wound-rotor motor, unlike a squirrel-cage induction motor, the rotor has coils connected to slip rings, which enables the adjustment of the rotor's resistance via external resistors. This feature assists in controlling the motor's performance characteristics such as starting current and slip.

In contrast, the squirrel-cage induction motor has a rotor constructed from conductive bars and does not require slip rings, as it relies on electromagnetic induction from the stator to create a rotating magnetic field. Similarly, the capacitor-start motor uses a capacitor to aid in starting but does not utilize slip rings. The synchronous motor operates with a rotor that is magnetically locked in synchrony with the rotating magnetic field of the stator, again not involving slip rings for rotor winding connections. Thus, the wound-rotor induction motor stands out for its unique use of slip rings, enabling specific operational advantages.