Fault diagnostics of induction motors based on internal flux measurement

A new fault diagnosis scheme based on the monitoring of main air gap flux of squirrel cage induction motors is proposed. Most of the existing flux monitoring techniques are based on the leakage or stray flux measurement outside of the motor. A few methods, however, use the main air gap flux as the fault signature, where search coils are used to monitor the derivative of the flux, which eventually introduces noise in the signal. Moreover, the diagnosis methods are mainly based on detecting a fault, whereas very little initiative has been taken to locate a fault precisely. To address these problems, a sophisticated yet robust condition monitoring and fault diagnosis method is needed. 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 magnetic flux, but also by magnitude and phase shift comparison of sensors located at different geometric positions around the stator. We have successfully detected the stator turn-to-turn fault at a very incipient stage and detected the location of the fault precisely. Promising results have been obtained through simulation in the case of broken rotor bar faults as well.