The Influence of Thermal Aging on the Surface Trap Characteristics and Surface Flashover of Epoxy Resin

Surface charge accumulation of epoxy resin is easy to cause surface flashover under DC voltage, and thermal aging is an important factor affecting surface charge and trapping characteristics. In this paper, the electron and hole trap characteristics of epoxy resin were studied by changing the polarity and amplitude of charging voltage. Then, the influence of thermal aging on the trap energy level distribution of epoxy resin is researched by conducting the thermal aging experiment, based on which the influence of the energy level distribution of electron trap on the negative DC flashover characteristics is furtherly studied. Experimental results show that the energy level of electron trap and hole trap on the surface of epoxy resin ranges from 0.70 eV to 0.96 eV, the peak energy level of hole trap is slightly higher than that of electron trap. The maximum of the density of trapped charge in the electron trap and hole trap is 1.98 x 1020eV-1 center dot m-3 and 1.82 x 1020eV-1 center dot m-3 respectively. The energy level of traps on the surface of epoxy resin generally shows a deepening trend after thermal aging. The peak energy level of electron trap increases from 0.84 eV to 0.98 eV after 29 d of thermal aging, which is due to the product containing strongly polar group produced by thermal aging. The results of flashover testing shows that the flashover voltage first increases and then decreases with the extension of thermal aging time. With the extension of aging time from 7 d to 29 d, the flashover voltage decreases by about 11.2%, the change of flashover voltage is related to the change of trap energy level distribution on the surface of dielectric. This paper can provide theoretical and experimental basis for the insulation design of epoxy resin applied in electric equipment.