Development and distribution of surface charge on epoxy resin under dc electric field in different gases

Under DC voltage, charge accumulates on the break insulation of mechanical DC circuit breakers, distorting the local electric field, which increases the risk of break insulation failure. Glass-fiber vacuum-impregnated epoxy resin can be used as an insulation material for DC circuit breakers owing to its excellent mechanical and electrical properties. We have created a system to measure the surface potential of an epoxy resin in different gases. The accumulation and dissipation of the surface charge in air and SF6 are determined, and the effects of air and SF6 are compared. The results show that the polarity of the surface charge is the same as that of the applied DC voltage, and that the main source of the charge is from Schottky charge injection. In SF6, the charge density is higher than that in air, and its decay rate is slower. The decay law of the surface potential in SF6 can be characterized by two exponential superposition formulas. In the early stage, surface charge is attenuated mainly by being transferred along the surface of the insulator and neutralized by gas ions. In the late stage, surface charge is attenuated mainly by transferring through the volume of the insulator.