Research On Gap Breakdown And Flashover Characteristics Of SF₆/N₂

SF₆was used in high voltage technology widely,which as an excellent insulation and arc extinguishing performance.However,it was limited to use because of the strong greenhouse effect and low liquefaction temperature,and there is urgent to study and develop SF₆alternative gas or gas mixture,so it has theoretical significance and practical value to carry out the research on the discharge characteristics of SF₆/N₂.In order to study the insulation characteristics of SF₆/N₂gas mixtures,two electrode structures of rod-plate and rod-rod were designed,SF₆/N₂mixed gas gap breakdown and flashover along insulator surface test platform built.Based on this platform,the SF₆/N₂gas gap breakdown and along-surface flashover tests were carried out at different gas pressures（0.4-0.7MPa）and different mixing ratio（SF₆volume fraction of 0,20%,30%,50%and 100%）to study the discharge characteristics of the SF₆/N₂gas mixture.The electric field distribution of the two electrode structures and the electric field distribution of the insulator surface were simulated by FEM software.In this paper,consider the Joule loss generated by GIS current and eddy current loss generated by metal shell induction,as well as heat conduction,heat convection and heat radiation,etc.,and apply finite element simulation software to build a three-dimensional model for multi-physics field coupling calculation to calculate the insulator temperature distribution is calculated,and the effects of different pressure,mixing ratio,operating current and ambient temperature on the insulator temperature distribution are studied and analysed.The research results show that the breakdown voltage of SF₆/N₂gas mixture in rod-plate electrode structure under the action of frequency voltage increases non-linearly with the increase of gas pressure and has obvious synergistic effect,30%SF₆/70%N₂gas mixture has the most visible synergistic effect.The breakdown voltage of N₂was obviously higher than the breakdown voltage of SF₆/N₂gas mixture when the gas pressure is the same for the rod-plate and rod-rod electrode structures under negative lightning surge voltage.The breakdown voltage of SF₆/N₂gas mixture is negative synergistic effect;when the volume fraction of SF₆gas is 20%,30%and 50%,the polarity effect of SF₆/N₂gas mixture lightning shock voltage is the same as SF₆and opposite to N₂.30%SF₆/70%N₂gas mixture in insulator concave flashover voltage is less than convex flashover voltage,the lightning shock negative polarity flashover voltage increases linearly with the increase of air pressure.The flashover voltage at gas pressure 0.5MPa is 93%of the flashover voltage of SF₆at 0.5MPa,and the flashover voltage at 0.6MPa has exceeded the flashover voltage of SF₆at 0.5MPa;the flashover voltage of 30%SF₆at 0.5MPa under industrial frequency is 89.5%of the flashover voltage of SF₆at0.5MPa,and the flashover voltage along the face of the insulator at 0.7MPa exceeds Flashover voltage of SF₆at 0.5MPa.The change in gas pressure and mixing ratio has no effect on the temperature at the shell,but has a greater effect on the temperature of the insulator near the guide rod,the load current affects the conductor and shell heat power and the insulator temperature distribution;the higher the ambient temperature the smaller the insulator temperature rise.