Fault Indicators for Stator Current Based Detection of Torque Oscillations in Induction Motors at Variable Speed Using Time-Frequency Analysis

This paper studies the detection of small torque oscillations in induction motor drives during speed transients by stator current analysis. Small torque oscillations can be the consequence of mechanical faults. Speed transients result in time-varying supply frequencies that prevent the classical current spectrum analysis. The proposed solution is time-frequency signal analysis. This work particularly deals with the extraction of fault indicators that could be used in a permanent and automatic condition monitoring system. Three different fault indicators based on instantaneous frequency estimation and the Wigner Distribution are presented. Their performances are tested on experimental signals from speed transients under different load conditions.