Influence of Electrical-Thermal Aging to the Bar-to-bar Discharge on the End-winding of HV Motors

The space left between adjacent coils on the end-winding can become inadequate during the operation of high voltage (HV) motors due to mechanical vibration or other factors, which can lead to bar-to-bar discharge in the small air gap between two adjacent coils and gradually develop into phase-to-phase or phase-to-ground failures. Additionally, the inadequate spacing can also result in poor heat dissipation, causing excessive temperature rise in the winding and further accelerating the insulation failure process. To better understand the development of bar-to-bar discharge, an accelerated aging experiment was conducted on two stator coils under well-controlled thermal and electrical stresses. The partial discharge (PD) was collected, and the characteristics of phase resolved partial discharge (PRPD) patterns were analyzed along with periodic visual inspection of the insulation surface. It was observed that bar-to-bar discharge always gives rise to constant amplitude during both half cycles of the voltage. Furthermore, the PD distribution changes from “strip-like” shape to “ rabbit-like ” and “ turtle-like ” shape as aging progresses. The PD inception phase shifts forward, approaching the zero crossings of the positive and negative half-cycles, while PD parameters show an increasing trend with aging. Additionally, corona discharge and surface discharge appear and gradually become the dominant discharge types. The research of this paper is devoted to provide a reference for PD monitoring and fault diagnosis of HV motors.