Surface flashover sustained by electrostatic surface charge on epoxy resin insulator in SF6

The importance of studying the influence of accumulated surface charge on surface flashover is demonstrated by on-site trapped charge measurements. Using a hemispherically tipped electrode on an epoxy resin plate, it has been shown that, at a critical surface energy density, a back flashover can be induced when the DC is suddenly removed. The back-flash threshold levels were measured at different pressures and for two electrode-insulator geometries. The concept of minimum surface energy density E_m capable of sustaining surface flashover was formulated. Various experimental observations can be interpreted by the concept, such as the aforementioned back-flash phenomenon, the close proximity to the insulator surface that flashover path tends to seek etc. From the measured back-flash threshold voltage and field analysis of the two geometries, the minimum surface energy density E_m necessary for sustaining continuous surface discharge has been calculated. The compilation of the results for both geometries at different pressures is presented.