Influence Of Micro Water On Power Frequency Insulation And Discharge Decomposition Characteristics Of C₄F₇N/CO₂ Gas Mixture

As one of the SF6 alternative gas with excellent insulation and environmentalfriendly performance,C4F7N/CO2 mixed gas has been applied in engineering at home and abroad.However,there is inevitably micro water in gas insulated equipment,existing research shows that micro-water may reduce the insulation strength of the gas,and then endanger the safe and stable operation of equipment,on the other hand,microwater may participate in the decomposition reaction of the insulating gas,which accelerate gas decomposition and insulation degradation.The influence of micro-water on the insulation and decomposition characteristics of C4F7N/CO2 mixed gas is still unclear,therefore,it is of great value to study the influence of micro-water on the insulation and decomposition characteristics of C4F7N/CO2 mixed gas.Firstly,power frequency breakdown test platform was built to study the influence of micro-water on the power frequency breakdown characteristics of C4F7N/CO2 mixed gas under different electric field forms and air pressure conditions,as well as the change of insulation performance of mixed gas after 300 breakdowns.The research results show that the average breakdown field strength of the mixed gas decreases with the increase of the non-uniformity coefficient of the electric field,and the power frequency breakdown voltage of C4F7N/CO2 mixed gas is significantly negatively affected by micro-water,in the range of micro-water content of 7μL/L to 1529μL/L,the maximum decrease of power frequency breakdown voltage of mixed gas is 26.1%.The breakdown voltage of the mixed gas with micro-water content of 1529μL/L decreased by 6.39%after 300 breakdowns,while the dry mixed gas only decreased by 1.77%.At the same time,the dispersion of breakdown voltage of mixed gas increases with the increase of micro-water content.Secondly,the power frequency surface flashover test platform was built,and the influence of micro-water on the power frequency surface flashover characteristics of insulators in C4F7N/CO2 mixed gas at different air pressures was studied.The research results show that the flashover voltage of insulator shows a weak saturation growth trend with the increase of air pressure,and the micro-water reduces the growth rate of flashover voltage with the change of air pressure.The power frequency surface flashover voltage of insulators decreases with the increase of micro-water content,when the micro-water content is less than 500μL/L,the maximum decrease of surface flashover voltage is 5.5%,while the maximum decrease is 8.8%as the micro-water content reachs 1500μL/L.Finally,gas decomposition test platform was built to study the effect of microwater on the decomposition characteristics of C4F7N/CO2 mixed gas under suspended partial discharge,as well as the gas insulation performance after discharge decomposition under different air pressures.The research results show that the microwater greatly promotes the discharge decomposition of the mixed gas,the gas production rate of CO,CF4,C2F4,C3F8,CNCN and CF3CN reaches 2.18 times,1.66 times,1.61 times,1.87 times,3.35 times and 2.2 times of the dry gas respectively,after 12 hours of discharge,the power frequency breakdown voltage of the mixed gas is 16.06%lower than that of the dry mixed gas before discharge.