Influence of Temperature on Developing Process of Surface Flashover in Oil-Paper Insulation under Combined AC-DC Voltage

In order to study the influence of temperature on surface flashover behavior with oil-paper interface under combined AC-DC voltage, a discharge test assembly was established to investigate the influence of temperature on developing process of surface flashover of oil-paper interface from 25 degrees C to 90 degrees C. Based on impulse current method, the process of surface flashover of oil-paper interface under combined AC-DC voltage was studied by electrodes configurations that simulated the tangential electric field and radial electric field of surface of pressboard, in which the voltage was increased step-by- step. Meanwhile the partial discharge (PD) spectrums at whole flashover stages were studied. Moreover, high speed camera was used to record the whole process of surface flashover which was divided into 4 stages: (1)Inception stage, (2)Streamer stage, (3)Intermittent breakdown stage, (4)Surface flashover stage. The experiments results shown that flashover voltage and PD inception voltage at high temperature (HT) was lower than the voltage at low temperature (LT). The average amplitudes of PD at LT were lower than at HT. The growth rate and repetition rate of PD at HT was faster than at LT. It was easier to develop the flashover at oil-paper interface under combined AC and DC voltage at HT. So the flashover voltage was lower at HT. the surface of pressboard was destructed severely at HT, the track of surface discharge was obvious at HT.