Understanding the effect of SiC/epoxy coating on surface flashover under DC voltage: from surface charge accumulation

Abstract

Charge accumulation at the insulator surface significantly alters the electric field distribution under DC voltage and can lead to unpredictable flashover. It is realized that the surface flashover voltage is reliant on the charge distribution approaching flashover occurrence (CDAFO). A method of how to judge the moment approaching flashover was proposed in this study to clarify how surface charges induced flashover, whereby the dynamic distributions of surface charges, including the CDAFO, were obtained from the instant of voltage application to the moment approaching flashover. The resulting flashover was analyzed with regards to insulators coated in SiC/epoxy, including an examination of the dominant charging pathway during voltage rising and a discussion of the relationship between the CDAFO and flashover voltage. Despite voltage polarities and SiC content, a reversal of charge polarity from hetero-polar to homo-polar was observed during voltage rising. Furthermore, it was discovered that the CDAFO was homo-charge accumulation, and an increase in SiC content resulted in greater homo-charges. A theory outlining homo-charge’s enhancement of flashover voltage by weakening the electric field near the high voltage electrode was also proposed. Consequently, because of the improved effect of homo-charges on flashover voltage, the addition of SiC led to the boost of flashover voltage.