Low Pressure Partial Discharge Tests with Ultra High dv/dt PWM Voltages for Aircraft Motor Windings

The use of wide-bandgap (WBG) semiconductor devices is increasing due to its relatively high efficiency and power density. These benefits make WBG device-based motor drives very promising for aviation applications, especially the More Electric Aircraft (MEA). However, WBG device-based motor drives, generally utilizing the Pulse-width Modulation (PWM) technique, can generate square-wave voltage pulses with very fast rise times down to tens of nanoseconds. Such changes in excitation may impact the behavior of partial discharge (PD) in aviation motor windings. Combining the impact of faster rise time PWM voltage with reduced air pressure, PD in aviation motor windings is a very interesting and essential research topic that needs to be addressed. Additionally, there has been a lack of aviation insulation test standards for PD test under such conditions. As a result, an appropriate qualification test method has not been well-defined. In this paper, pulse PD tests are conducted on a motorette sample to provide insights on both issues. A test setup including an ultra-high dv/dt PWM pulse generator and associated PD sensors, is introduced. Experimental results for the motorette sample in air at 87 Torr, under PWM excitations with fast rise times (60 ns), are presented. The tests are conducted from 1 kHz to 10 kHz and duty cycles at 0.2 and 0.5. The impacts of repetitive pulse train frequencies and duty cycle are shown. A discussion on the appropriate PD qualification test condition for low pressure aviation motors, driven by WBG device-based converters, is also included.