Effects of arc ablation on surface electrical performance of epoxy resin insulation

Abstract

Operation of a high-voltage, direct current circuit breakers can cause irreversible damage to the surface electrical performance of insulation due to arc ablation. To analyze the failure mechanism, the epoxy resin (EP) insulation was ablated under experimental arcs of different energy values. The rated current of the experimental arc is 5 A, and the ablation energy values were set as 0 J, 31.3 J, 78.2 J, 109.6 J and 156.5 J respectively by changing the arc duration. The destruction of the EP surface molecule structure was investigated by using x-ray photoelectron spectroscopy and gas chromatography. Furthermore, the surface potential decay and distribution characteristics of surface traps were studied by using the isothermal surface potential decay (ISPD) method. The test results indicate that when arc energy reaches 156.5 J, the DC flashover voltage of EP decreases by 64.7% and the surface conductivity increases by 3.22 times, compared with that of the virgin sample. Reductive groups in EP molecules are oxidized when suffering arc ablation, thereby leading to the breakage of molecular chains and severe carbonization, forming amorphous carbides with high conductivity on EP surface. ISPD results show that the density of deep traps and the center energy level of traps on the EP surface increase when the arc energy increases. These traps can form multiple charge centers and distort the electric field distribution on the EP surface. Thus, the partial discharge is promoted and flashover finally occurs, thereby decreasing the surface electrical strength of EP.