Fault diagnosis of induction motors by space harmonics analysis of the main air gap flux

A new fault diagnosis scheme based on the monitoring of main air gap flux of the three phase squirrel cage induction motor is proposed. Most of the existing electrical techniques of condition monitoring are based on the stator current and/or leakage flux measurement outside the motor. Besides, most of these methods only concentrate on the time harmonics analysis of the acquired signal. We propose to analyse the space harmonics of the main air gap electromagnetic flux along with the time domain analysis. To this aim, we propose to monitor the main air gap flux using Hall Effect Flux Sensors (HEFS) at all the stator slots of an induction motor, which can be used to address the stator and rotor slot effects not only through frequency analysis of the time varying magnetic flux, but also by magnitude and phase shift comparison of sensors located at different geometric positions around the stator. Moreover, by using HEFS in all the stator slots, the flux density along the circumference of the stator can be acquired and the space harmonics of the flux can be analysed, which shown promising results in detecting and locating different faults. In this paper, we concentrate on detecting different types of rotor faults such as broken rotor bar fault and eccentricity.