Study On Distribution Of Surface Conductivity Of Epoxy Resin And Its Effect On Surface Electrical Properties

Gas insulated transmission line(GIL)has become the preferred alternative to traditional overhead lines,cables,and wall bushings due to its good insulation performance,low loss,small footprint,and high reliability,and is widely used in highvoltage long-distance power transmission.Insulators made of epoxy resin(EP)as the main material are the key protection link in the GIL operation.It has multiple functions such as mechanical support and electrical isolation.It’s safe and stability is of great significance to the reliability of power equipment and power systems.EP tends to accumulate a large amount of charge on the surface under the high voltage DC electric field,which leads to the decrease of insulation performance and the increase of potential safety risks in the power system.Therefore,this thesis uses a combination of simulation calculation and experimental verification to explore the influence of surface conductivity distribution on the electrical properties of the EP surface,to achieve the purpose of optimizing the insulation performance along the surface.First,build a transient field simulation model of the gas-solid composite insulation system under DC voltage.The study found that: under the needle-needle electrode,the electric potential and electric field strength distributed axially symmetrically;the surface charge distributed in bipolarity: negative charges accumulate near the high-voltage electrode,and positive charges accumulate near the ground electrode,which is symmetrically distributed in the center.The maximum value of the electric field intensity and the surface charge density at the gas-solid interface appears at the three junctions of the high-voltage electrode,solid insulating material,and gas dielectric.Then,uniformly distributed surface conductivity was applied to the simulation model.The results showed that: within the range of conductivity,as the surface conductivity increases,the maximum electric field intensity at the interface first decreases and then increases,but the increment is very small.The maximum surface charge density at the triple junction first increases and then decreases with the increase of conductivity,and finally reaches a steady-state value.To verify the simulation results,the EP sample was uniformly modified using the DBD plasma physical etching surface modification platform,and the performance of the modified sample was tested.Studies showed that as the modification time increases,the surface roughness and the surface conductivity of the sample gradually increases.The optimal modification state is reached when the modification time is 4 min.The flashover voltage,the maximum surface charge density,and the surface conductivity are positively correlated,and the experimental results are highly consistent with the simulation calculation results.Finally,based on the idea of giving different surface properties to different areas,a step gradient distribution of surface conductivity is applied to the simulation model for the extremely uneven electric field under the needle-needle electrode.The results show that: compared with the surface conductivity in the low-field-strength area,the surface conductivity in the high-field-strength area has a greater impact on the gassolid composite insulation system.The change rule is the same as that under the uniformly distributed surface conductivity.The surface electric field and the surface charge distribution under step gradient settings are better than those under uniform settings.The step gradient distribution of different modes also influences the electrical performance of the composite system.The electrical performance under the "high-lowhigh" distribution mode is better than the "low-high-low" mode.To verify the simulation results,the APPJ plasma physical etching surface modification platform was used to modify the EP sample in a steep gradient,and the performance of the modified sample was tested.Studies show that: similar to the results of physical etching modification on the surface of DBD,APPJ modified samples,as the modification time increases,the surface roughness and the surface conductivity gradually increases.The best modification condition is reached at 4 min.The high and low field strength regions of the sample were treated at different times and the samples were tested for their surface insulation properties.The results show that the surface conductivity of the sample with a step gradient distribution law,along with the surface flashover voltage and the maximum surface charge density is higher than the sample with a uniform distribution law.The surface conductivity of the sample with the "high-low-high" step gradient distribution law is better than that of the "low-highlow" distribution.The experimental results are in good agreement with the simulation results.In this thesis,the realization of surface conductance distribution rules of epoxy resin and its influence on the electrical properties of EP surface is deeply explored and verified,which will help to further provide basis and guidance for the modification of insulating medium and insulation optimization.