Effect of the repetition frequency and polarity of square wave voltage on the partial discharge of electric machine insulation for more electrical aircraft

Abstract More electric aircraft (MEA) are featured with the electric propulsion system, which is more efficient and environmentally friendly than traditional aircraft. Partial discharge (PD) caused by high-frequency square wave electrical stress and environmental stress is the main reason for the failure of electric machine insulation for MEA. To study the effect of the repetition frequency and polarity of square wave voltage on partial discharge characteristics, a partial discharge detection platform is set up, using an ultra-high-frequency (UHF) down-mixing method and optical method to detect PD. These two methods are proven to be effective in measuring the PD impulse signal under square wave voltages. Meanwhile, considering the actual operating condition of MEA, the high voltage square wave is applied on samples of twisted pairs under different air pressures (down to 20 kPa) and different repetition frequencies (up to 5 kHz). The results show that the increase in the frequency of the square wave and the decrease in air pressure lead to a lower PDIV. In addition, electric field distribution under square wave voltage of different polarities and frequencies and the dielectric relaxation process of gas-solid composite insulation for electric machine insulation are analyzed to explain the results physically.