Surface Potential Dynamics and Flashover Resistance Evaluation of Epoxy Resin Under DC Flashover

To explore dc flashover characteristics and evaluate the dc flashover resistance of epoxy resin, an online surface potential measurement is proposed and verified in this article. Rising positive and negative dc high voltages (HVs) with a step of 0.5 kV per 5 min are applied to epoxy resin until the intensive flashover occurs, and the surface potential at the triple junction point is measured during flashover. It is found that the surface potential profile appears as the recurrence of flashover units during intensive flashover. A three-point peak-finding algorithm with threshold judgment is proposed to determine the interval between adjacent flashover units. Both appropriate surface potential difference threshold (SPDT) and flashover interval (FI) are used to evaluate the severity of flashover (i.e., the opposite of flashover resistance). It is interesting to find positive and negative flashover has different surface potential evolution characteristics. Positive flashover exhibits larger fluctuation, higher SPDT, and shorter FI, which may result from severe positive charge accumulation before every single flashover due to the low surface mobility of the positive charge. The results manifest positive flashover is more serious than negative flashover for the investigated epoxy resin.