Plasma Gradient Treatment And Its Effect On Surface Electrical Properties Of Epoxy Resin

Gas insulated metal closed transmission lines（GIL）have been widely used due to their large transmission capacity,small capacitive load,and small impact on the geographical environment.However,the Epoxy Resin（EP）basin insulator inside the GIL will accumulate a large amount of surface charge during long-term operation,which will cause flashover along the surface,which will seriously damage the insulation performance and threaten the safe and stable operation of electrical equipment.At present,most of the surface modification of epoxy resin is uniform treatment,but the electric field environment of the insulator is not evenly distributed under actual working conditions,and the uniform surface modification method is difficult to achieve the optimal effect.Therefore,this article uses Atmospheric Pressure Plasma Jet（APPJ）technology to perform gradient modification on the EP surface.The surface physical and chemical properties and electrical properties of the samples before and after treatment were discussed,and the gradient distribution of surface charges and electrical parameters were constructed.Achieve the effective regulation of surface insulation performance.Firstly,the atmospheric pressure plasma jet（APPJ）gradient modification platform,the insulation material surface charge dynamic scanning platform and the flashover voltage test platform are built.Through the gradient physical etching of epoxy resin,the influence of the gradient distribution of surface physical morphology on the electrical properties of epoxy resin surface is studied.The results show that the plasma gradient physical etching makes the surface roughness of the material present a gradient distribution,and the surface conductivity and surface charge dissipation rate are both improved.The flashover voltage of the modified sample reached 11.2k V,which was nearly 20%higher than that of the untreated sample.Secondly,in order to study the effect of chemical gradient modification on the electrical properties of EP surface,CF₄and TEOS are used as precursor to treat the epoxy resin surface with plasma fluorination gradient and silicon deposition gradient treatment.The mechanism of the process is explained by the experimental results and COMSOL simulation results.The study found that the two gradient modifications can change the surface roughness of the insulating material,improve the surface conductivity of the insulating material,and the surface charge dissipation rate.Under the fluorinated gradient treatment,the flashover voltage of the samples reaches 11.7k V,which is nearly25%higher than that of the untreated samples.Under the silicon deposition gradient treatment,the flashover voltage reaches 14.5k V,which is nearly 50%higher than that of the untreated samples.In addition,the influence of plasma multi-element gradient treatment on the surface electrical properties of epoxy resin is studied.The F-Si-F combination gradient and Si-F-Si composite gradient are taken as examples.It is found that the flashover voltage of modified EP by multi element combination gradient is significantly improved compared with the untreated and other gradient treated samples.Especially for the Si-F-Si composite gradient,its flashover voltage reached 16.2k V,which is nearly doubled compared to the untreated sample.Finally,the mechanism is explained as follows:through COMSOL simulation,it is found that the surface conductivity gradient distribution can effectively optimize the electric field distribution on the epoxy resin surface under the needle-needle electrode.The uniform modification of the surface makes the surface characteristics of the epoxy resin evenly distributed,and the charge moves rapidly from the high-voltage electrode to the ground electrode,resulting in more charges participating in the discharge and limiting the effect of improving the flashover voltage.Gradient modification can accelerate the surface charge dissipation rate in the high-field-strength area,control the surface charge dissipation rate in the low-field-strength area,thereby inhibit surface discharge,and maximize the flashover voltage.In conclusion,the surface gradient modification method proposed in this paper provides a new method for improving the surface insulation performance of insulating materials.