A “superimposed frequency” motor test

Feeding 3-phase currents to the slip rings of induction motors at slip frequency for speed regulation or phase advancing (power factor improvement), or at any other frequency for other purposes is used frequently and the principle is well known. Another possible application of this principle is that of testing induction motors under full current loading conditions, while running at full speed, with the stator supplied at full voltage and frequency, and without the use of any kind of loading machine. This results in a large saving of energy because the run is taken at near zero power factor for primary and secondary supply.