Slip ring

A slip ring is a ring-shaped piece of copper that allows current to pass through the winding via sliding contact. However, it is not intended for commutation as in DC motors and AC commutator motors. There are three motors that use this:
(1) Winding type induction motor: (fig. a)
(2) Variable Field Synchronous Motor: (fig. b)
(3) Rotary armature type motor (double-rotor motor): A motor with a structure in which the stator (armature) of a normal synchronous motor or brushless motor rotates in one direction, while the rotor rotates in the opposite direction. Power is supplied to the armature through the slip ring. The purpose is to gain (increase) the speed relative to the armature even if the rotor is turning at low speed or stopped.