Influence mechanisms of epoxy degradation on surface traps and charge accumulation under DC electrical-thermal stress

As trapping sites for surface charges, the surface trap is an important factor affecting the insulation performance of the epoxy-SF6 interface, which is closely related to the microstructure and its evolution. However, existing studies often ignore the effect of the degradation of the epoxy surface on the surface traps and charge accumulation during the long-term service of the insulation system. In this study, the surface physicochemical evolution and its influence on surface traps of a typical epoxy-SF6 insulation structure were researched under a DC-temperature gradient condition, and an evolution mechanism of surface traps was proposed. The results show that the free radicals introduced during the material degradation process increase the density and depth of both positive and negative charge traps on the epoxy surface. The effect of free radicals formed by the cleavage of epoxy molecules on the electronic orbital and molecular electrostatic potential of epoxy molecules is the intrinsic reason for the evolution of surface trap evolution. This work may help to understand the long-term evolution mechanisms of the physicochemical characteristics of the epoxy-SF6 interface in DC field and may provide a theoretical basis for the long-term failure mechanism revealing and the insulation performance enhancement.