Partial Discharge Phenomena in Electrical Machines for the More Electrical Aircraft. Part II: Impact of Reduced Pressures and Wide Bandgap Devices

Abstract

This paper focuses on the inception of partial discharges within the insulation system of electrical actuators used for the More Electrical Aircraft (MEA). Since these machines should operate in the absence of Partial Discharges (PDs), the dependence of the PD Inception Voltage (PDIV) on voltage impulses typical of wide bandgap (SiC) devices is investigated at both 1 bar, reduced pressures close to those typical of aircraft cruising altitudes (150 mbar-200 mbar) or lower (down to 5 mbar). Propagation issues are not dealt with here as results were obtained working on insulation models consisting of couples of wires twisted together (twisted pairs), thus knowing exactly the potential differences between all points of the insulation model. The results show that the rise times and the switching frequencies associated with wide bandgap devices have little impact on the PDIV. A model able to predict the PDIV of the turn/turn insulation of random wound motors (the most vulnerable part of the insulation) at different pressures is proposed. The model is also able to deal with temperature changes, with limitations that depend on the type on insulation systems. INDEX TERMS Partial discharges, More Electrical Aircraft, MEA, wide bandgap devices, SiC inverter, Qualification. I.

Reliability-Oriented Design of Inverter-Fed Low-Voltage Electrical Machines: Potential Solutions

“…In general, the PDIV decreases with the increase of temperature and the reduction of pressure. When the pressure goes below a certain threshold, PDIV increases with the further decrease of pressure as shown in Figure 12 [138].…”

“…To pursue high-performance EMs, understanding the physics of partial discharge is necessary instead of adopting the empirical enhancement factor. Many works dedicate to investigate the influence factors on PDIV or RPDIV of turn/turn insulation [54,62,120,123,[138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153] through experiments. A typical experiment setup for PDIV investigation is presented in Figure 11.…”

“…Both temperature [54,62,120,123,[140][141][142]155] and pressure [120,138,[142][143][144]152,153] have great impact on the PDIV. In general, the PDIV decreases with the increase of temperature and the reduction of pressure.…”

“…The impulsive voltage caused by the inverter may influence PDIV although t is also not highlighted in the standards. Typically, a surge voltage is characterized time, repetition frequency, and duty cycle and a couple of work studying the influ PDIV can be found for each topic: rise time [62,130,138,148], frequency [138,[143][144][145][146][147][148][149]153], and duty cycle [147,148]. To account for the potential insulation challeng by the WBG device, some papers have conducted the investigation based on th device.…”

“…To account for the potential insulation challenge caused by the WBG device, some papers have conducted the investigation based on the WBG device. The rise time can be down to 7 ns [138] with a slew rate of 140 kV/µs and the switching frequency can reach 600 kHz [159]. Unfortunately, there is no general conclusion that can be drawn based on these papers since the test voltage conditions are quite different and the PDIV may be affected by the combination of rise time, frequency, and duty cycle.…”