Analytical Investigation of the Humidity Effects on Repetitive Partial Discharge Inception Voltage in Inverter-Fed Motor Windings

Abstract

Inverter-fed motors are exposed to high dv/dt surge voltages that can initiate partial discharge (PD) in winding insulation, particularly under humid operating conditions. This study examines the effects of humidity on the repetitive PD inception voltage (RPDIV) using twisted-pair samples and a SiC-MOSFET-based pulse power supply. Experimental results show that RPDIV decreases with increasing humidity. Analysis based on the volume-time theory indicates that this reduction is primarily caused by an increase in the electron emission from the insulation coating, while the influence of electron detachment from negative ions in air is negligible even in the high-humidity environment.