Partial Discharge Investigation of Form-Wound Electric Machine Winding for Electric Aircraft Propulsion

Electric machine for aircraft propulsion is required to have high power density and high reliability, but the harsh operating environment, such as low air pressure, will challenge the motor's insulation system. This article presents the partial discharge (PD) investigation of the form-wound winding in high-frequency electric machines for electric aircraft propulsion. Experimental results show that the PD activity is largely enhanced due to the decrease in air pressure. PD inception voltage (PDIV) decreases to 50%-60%, and the PD magnitude dramatically increases when the pressure drops from 1 to 0.2 atm. Several windings with introduced defects were also tested to extract features from phase-resolved PD (PRPD) analysis, which can be used for PD pattern recognition. In addition, a PD-based failure precursor, combining the apparent charge, number, and phase interval of the monitored PD profile, is proposed to monitor the insulating condition of the thermally and electrically aged windings. The proposed failure precursor generally shows a rising trend with the aging time in this article. The application of the proposed failure precursor on online condition monitoring needs more investigation through long-term online observation of the electric machine.