Determination of Rotor Slot Number of an Induction Motor Using an External Search Coil

This paper describes determination of the number rotor slots of an induction motor from the induced emf in an external search coil. This information is needed in prediction of motor speed from the external search coil induced voltage. The approach is based on identifying saliency harmonics and rotor slot harmonics, via FFT analysis of the external search coil emf. The proposed approach is tested on an induction motor driven by the mains supply. The experiments are repeated with a PWM supply. It is shown that the method works well in both cases and the number of rotor slots of the test machine is accurately predicted