A generalized equivalent circuit in the theory of polyphase commutator motors

The demand for speed variation and power-factor compensation in a-c motors led to the development of the polyphase commutator types. In their simplest form these motors consist of two windings; a stator winding which is identical with that of the polyphase induction motor and a rotor winding of the closed type provided with a commutator and similar to the winding of a d-c armature. The field and armature windings are connected in series or shunt and give load characteristics similar to their d-c counterparts.