Evaluation of current and vibration signals for squirrel cage induction motor condition monitoring

This paper reviews aspects of online condition monitoring techniques for detecting broken rotor bars in squirrel cage induction motors, by evaluating both current and vibration signals and taking cognisance of interbar currents. The paper shows that significant interbar currents reduce the unbalance brought about by a broken rotor bar, and thus why it is necessary to focus attention elsewhere in the current spectrum to diagnose a broken bar. This paper also explains the technique of monitoring the vibration spectrum and the effect of interbar currents which produce tell-tale components in the vibration spectrum. Two separate online condition monitoring techniques can be used in conjunction with one another to provide an accurate diagnosis of squirrel cage induction motors with broken rotor bars. The theoretical and experimental results provide significant proof of the validity of these two online condition monitoring techniques. The natural progression is to provide a software program to perform the intricate mathematical analysis for industrial use.