Partial discharge inception voltage under surge voltage application influenced by surface charge on insulating sheet

To understand the discharge characteristic under surge voltage application, the partial discharge inception voltage (PDIV) was investigated by using sphere-plane electrode under surge voltage application. Polyimide sheet with thickness of 0.125 mm was placed on the plane electrode and the air gap between the spherical electrode and the polyimide (PI) sheet was set to 0.1 mm. As the result, PDIV under surge voltage application was higher than that under DC voltage application. In addition, in both surge voltage application and DC voltage application, the negative PDIV was lower than positive one. This is because that the appearance probability of the initial electron is changed by voltage waveform and voltage polarity. In case of PI with surface charge, PDIV was changed according to surface potential value and PDIV without surface charge was almost the same as PDIV subtracted the surface potential value. From this result, the measurement scatter of PDIV might be small by considering the surface charge condition.