Understanding surface charging phenomena on alumina/epoxy spacers with surface conductivity gradient coating

Surface charge accumulation phenomena greatly restrict the development of DC power equipment. Suppressing surface charges are of great significance to promote surface insulation strength of polymeric dielectrics. In this study, we report surface charge and flashover regulation on alumina/epoxy spacers by graded conductivity coatings under DC voltages. The spacer surface is divided into different circular-ring areas from high voltage (HV) to grounded (GND) electrode. High conductive coatings consisting of titania particles of different contents and epoxy matrix are fabricated to spray on different circular-ring areas of spacer surface, which forms graded distribution of conductivity. Surface charge distribution on epoxy-based spacers is obtained by a Kelvin electrostatic probe after DC charging. Flashover voltage is measured in 0.1MPa 15%SF
₆
/85%N
₂
mixtures. The results show that graded conductivity coating can achieve excellent control of surface charge accumulation, and therefore improve flashover performance.