Power-factor improvement in cage-rotor induction motors

Rotating-field theory is used to develop a generalised expression for a cage induction motor with any stator winding connection and any supply configuration. This expression is shown to indicate that a cage induction motor will always draw positive VArs from the supply. The possibility of improving the power factor by means of stator-excited harmonic fields is examined, and the theoretical possibility of using subharmonic fields for this purpose is discussed.