Electric Field Regulation And Flashover Characteristics Of Epoxy Insulator Interface In HV Gas Insulated Apparatus

High voltage gas insulated apparatus,such as gas insulated line（GIL）or gas insulated switchgear（GIS）,is the key apparatus for scale utilization of new energy and enhancing the ability of power grid to resist natural disasters.Epoxy insulators are main components in gas insulated apparatus,but electric field concentration at gas-solid interface induced flashover faults of insulators have become one of the technical bottlenecks restricting the performance improvement of appatatus.It is of great significance to study the methods of regulating and optimizing the electric field distribution of gas-solid interface for promoting the reliability and miniaturization of power equipment.In this thesis,the concept of surface functionally graded materials（SFGM）was proposed and applied to insulator surface.The electric field regulation mechanism and effect of SFGM insulators in AC system were studied by theoretical analysis,simulation calculation and experimental test to provide theoretical basis and experimental support for the design,manufacture and operation of high voltage gas insulated apparatus.The main work is as follows:（1）Based on the classical electromagnetic field theory,the electric field distributions along the surfaces of the traditional insulator,C-uniform insulator and C-SFGM insulator were deduced.It is found that under ideal conditions,the electric field distribution along the traditional insulator surface is proportional to r^-2（insulator radius）,which is extremely uneven.The electric field strength along the C-uniform insulator is proportional to r^-1,which is more uniform than that of the conventional insulator.The electric field distribution along the C-SFGM insulator can be uniform by dielectric gradient design.（2）The application and effect of FGM and SFGM in electric field optimization of220 kV basin insulator are studied by simulation.It suggested that the maximum electric field strength of concave surface of the optimized FGM insulator is decreased by about 37%compared with that of the conventional insulator,but the leakage current is increased by 4.3 times.The maximum electric field strength of concave and convex surfaces of the optimized SFGM insulator are decreased by 30%-34%compared with that of the conventional insulator,and the leakage current of the insulator increases by about 30%.The leakage current of the SFGM insulator is much lower than that of the FGM insulator with the same electric field regulation effect.Therefore,the SFGM insulator has a broader application prospect.（3）The microstructural and dielectic properties of BaTiO₃ sputtering layer on the insulator surface prepared by magnetron sputtering were measured.It is found that with increasing sputtering time,the sputtering layer thickness increases exponentially.At room temperature,the relative permittivity value of sputtering layer under 50 Hz is about 1600.The relative permittivity of sputtering layer decreases with the increase of frequency because of the dielectric relaxation.The relative permittivity of BaTiO₃sputtering layer is less than 30 when the frequency is higher than 10⁴ Hz.（4）The traditional insulator,C-uniform insulator,discrete C-SFGM insulator and continuous C-SFGM insulator were fabricated.The electric field distribution and insulation performance along different insulators surface were studied by electric field simulation and flashover experiments.It is found that compared with the traditional insulator,the C-uniform,discrete C-SFGM and continuous C-SFGM insulators can improve the uniformity of electric field distribution along the insulator surface.Among them,the C-uniform insulator has“saturation effect”of electric field regulation,while the discrete C-SFGM insulator can break through this“saturation effect”and further reduce the maximum electric field strength of insulator,and the flashover voltage can be increased by about 20%.The continuous C-SFGM insulator after optimization can avoid the electric field distortion between gradients of the discrete C-SFGM insulator.The continuous C-SFGM insulator after optimization possesses the best electric field regulation ability and insulation performance among all kinds of insulators.