Combined Effect of Short Rise Time and Relative Humidity on the Partial Discharge Inception Mechanism in Rotating Electrical Machines Insulation

Electrical machines (EMs) operated on high-voltage dc buses for contemporary transportation applications are significantly exposed to the risk of partial discharge (PD). The inception mechanism of PD is influenced by various factors, including pressure, temperature, and humidity. With the increasing interest in SiC-based inverters, the impact of rise time on PD has garnered significant attention. In this study, a comprehensive measurement of PD inception voltage (PDIV) is conducted using test voltages with five different rise time values under five relative humidity (RH) levels at 30 ◦C. The experimental results indicate that within the range of 30–200 ns, the rise time has minimal impact on PDIV, while voltage overshoot significantly affects PDIV in high-humidity environments.