Discharge Characteristics of an Insulator Creepage Surface under Various Humidity Conditions

In this study, the discharge characteristics of an insulator creepage surface with a back electrode under various humidity conditions were experimentally investigated. Partial discharge (without sparks) was detected at a lower voltage than that of the arc discharge (short-circuit failure with sparks). The partial discharge inception voltage (PDIV) under the DC voltage was increased at high humidity. Meanwhile, the PDIV under the AC voltage was decreased at high humidity and was lower than that under the DC voltage. This finding indicates that the amount of charge on the creepage surface induced by the applied voltage increased under the high-humidity condition: The surface charge relaxes the applied electric field under the DC voltage, whereas it enhances the applied electric field under the AC voltage due to the delay in the surface charge distribution against the voltage polarity change.