Partial Discharge Characteristics of Epoxy Resin Under High-Frequency Pulse Electrical Stress

The application of wide-band gap (WBG) semiconductor devices is extremely beneficial to the compact design and power conversion efficiency enhancement of high power medium voltage (MV) power electronic transformers (PETs). However, the insulation system is exposed to high frequency and high slew rate (dv/dt) electrical stresses, the defect induced partial discharge (PD) is more severe, which can significantly affect life and reliability. PD tests on casting epoxy resin are carried out using high-frequency pulse voltage at the slew rate of 70 kV/ μs with the repetitive frequency ranging from 10 kHz to 100 kHz. Subsequently, the insulation degradation caused by frequency-induced PD is explored based on physical and chemical techniques. The results reveal that the degree of PD intensifies with the increasing frequency. The discharge repetition rate increases by 1220% at 100 kHz, the cumulative discharge amplitude increases by 41.8%. The frequency-induced heating effect becomes more significant as the frequency increases, while the insulation damage can be reflected by changes in morphology, chemical bonding, carbon and oxygen content. The degradation of epoxy resin is more obvious at higher frequency, the atomic content of carbon and oxygen decreases by 17.06% and increases by 11.4%, respectively, with a large number of bond breaking changes. While it tends to increase working frequency of MV PET utilizing WBG, leads to challengeable insulation degradation, which must be considered during the preparation of epoxy resin.