Stator current frequency analysis for condition monitoring of induction motors. II. Variable supply frequency

This paper describes three methods for the detection of rotor damage in an induction motor controlled by a variable frequency drive. They are (i) synchronous sampling of the stator current waveform using phase locked loop circuitry, (ii) time-frequency and wavelet analysis of stator current, and (iii) frequency spectrum analysis of the instantaneous input power of the motor. Experimental results from the three methods are presented. Some conclusions are drawn for the application to condition monitoring.