A Non-Intrusive Leakage Flux Based Method for Detecting Rotor Faults in the Starting Transient of Salient Pole Synchronous Motors

Damper and field windings are critical components of wound field synchronous motors (WFSM), where failure can lead to forced outage of the motor and industrial process. Due to the relatively rare presence of WFSMs in industry compared to induction motors, research on fault detection techniques for WFSMs is not as active. Rotor fault detection in WFSMs is also difficult, as synchronous operation leaves damper bars inactive during steady state operation while a small number of shorted field windings do not cause noticeable asymmetry. Therefore, most of the field-wide accepted tests rely on off-line testing or visual inspection of the rotor, or require airgap flux measurements, which necessitate motor disassembly and/or installation of sensors. Hence non-intrusive test methods which do not require motor disassembly are sorely needed to guarantee continued operation of the motor and industrial process. In this article, novel test methods based on the use of the leakage flux measured via search coils placed externally on the motor frame are proposed. A non-intrusive method for detecting and distinguishing damper and field winding faults during motor starting is devised from the time and frequency domain analysis of leakage flux and current. The methods are verified via experimental testing on a 30-kW salient pole WFSM.