Research On The Insulation Property Of CF₃I/Air Mixture

CF₃I is one of the most promising environmentally friendly insulating gases to replace SF₆ because of its excellent insulation performance and little impact on the environment and climate.Due to its high liquefaction temperature,it is often necessary to add buffer gas.In previous studies,N₂and CO₂ are often used as buffer gases for CF₃I,but few researchers have studied the insulation performance of CF₃I/air mixture.In this paper,the insulation performance of CF₃I/air mixture is studied by theoretical calculation and experimental analysis.Firstly,the electron swarm parameters of CF₃I/air mixture are obtained by solving Boltzmann Equation,to be compared with SF₆,CF₃I/N₂ and CF₃I/CO₂.The result shows that the insulation performance of CF3I/air in uniform electric field is similar to that of CF₃I/N₂ and CF₃I/CO₂.When the mixing ratio of CF₃I reaches 60%,the reduced critical electric field of CF₃I/air exceeds SF₆.Then,breakdown tests of CF₃I/air mixture are operated with power frequency and lightning impulse voltages respectively.Power frequency breakdown characteristics and lightning impulse breakdown characteristics of CF₃I/air mixture at different gap distances,pressure and mixing ratio are obtained,to be compared with SF₆.The breakdown characteristics of CF₃I/air mixture perform differently under different types of electric field and voltage.CF₃I/air mixture with CF₃I content 20%³0%has the most potential to replace SF₆.Its insulation strength is about 0.6¹.3 times of SF₆ according to the electric field inhomogeneity and voltage type.Finally,the decomposition products of CF₃I/air mixture after power frequency and thunder discharge were detected by GC-MS.Frequency discharge products of CF₃I/air mixture are CF₄ and C₂F₆.CF₃I/air mixture does not produce detectable fluorine-containing gas after lightning impulse discharge.