Investigation On The Synergistic Effect Of Environmental Friendly CF₃I Gas Mixtures

SF₆ gas has been widely used in the power system,however,it has a strong greenhouse effect and extremely difficult to decompose into the atmosphere.The continued use of SF₆ gas is not in line with China's goal of developing a cleaner and environmental friendly power system.Therefore,finding new insulating gas is one of the key issues that the power industry needs to address urgently.CF₃I gas is a kind of environmental friendly insulating gas which has the potential to replace SF₆ gas and there have been many studies about CF₃I and its mixtures.But the synergistic effect on CF₃I gas mixtures are less.Synergistic effect is a kind of interaction phenomenon between component gases of gas mixture,Reasonable utilization can effectively improve the insulation strength of gas mixture.However,it is still not clear whether external macroscopic variables such as voltage,gas pressure and electrode distance are related to the synergistic effect of CF₃I gas mixtures and it is difficult to guide the design of gas-insulated power equipment using CF₃I gas mixtures.Therefore,the synergistic effect of CF₃I gas mixtures and its influencing factor have strong research value for the application of environmental friendly insulating gas in power equipment.In this paper,the gas mixtures composed of CF₃I and N₂,CO₂ and CF₄ is studied theoretically and experimentally.Firstly,the Boltzmann equation is used to calculate the transport parameters such as the ionization coefficient and electron adhesion coefficient of the gas mixtures containing CF₃I,and the critical electric field strength value and synergistic effect coefficient of the gas mixtures at different mixing ratios are obtained.The results show that the insulation strength of the gas mixtures from strong to weak is CF₃I/CF₄>CF₃I/N₂>CF₃I/N₂O>CF₃I/CO₂.The synergistic effect of CF₃I gas mixtures from strong to weak is CF₃I/CO₂>CF₃I/N₂O>CF₃I/N₂>CF₃I/CF₄,in which the CF₃I/CF₄ gas mixture has no synergistic effect,and the CF₃I content is about 15%when the synergistic effect coefficient of the other three gas mixtures is maximum.In order to obtain the microscopic influence factors of the synergistic effect,the vertical ionization energy,vertical electron affinity energy,adiabatic electron affinity energy and adiabatic ionization energy of 10 kinds of buffer gas are determined by density functional theory.The relationship between the synergistic effect coefficient and microscopic parameters of various CF₃I gas mixtures was analyzed by mathematical statistics method.The results showed the relationship between adiabatic ionization energy,adiabatic electron affinity and electron static polarizability and synergistic effect coefficient is more significant,and the correlation coefficient R² is 0.664.On the basis of theoretical calculation and regression analysis,the synergistic effect of CF₃I/N₂,CF₃I/CO₂ and CF₃I/CF₄ gas mixtures was verified by the experimental platform.Under the slightly uneven electric field and normal pressure,both CF₃I/N₂ and CF₃I/CO₂ gas mixtures showed synergistic effect,but CF₃I/CF₄exhibited a significant negative synergistic effect.The breakdown voltage of the three gas mixtures from strong to weak is CF₃I/N₂>CF₃I/CF₄>CF₃I/CO₂.The influence of external macroscopic factors may be the main reason for the difference between theoretical and experimental results.Therefore,the effects of macroscopic parameters such as voltage type,gas pressure and electrode gap distance on the synergistic effect of gas mixtures are studied:increasing pressure and increasing the electrode gap distance can enhance the synergistic effect of CF₃I/N₂ gas mixture,due to the breakdown abnormality of CF₃I/CO₂,the negative synergistic phenomenon occurs in the gas mixture under certain pressure and distances.CF₃I/CF₄ gas mixture changes from negative synergistic effect to synergistic effect as the pressure and gap distance increase.The synergistic effect of CF₃I/N₂ and CF₃I/CO₂ gas mixture under extremely uneven electrical field is stronger than that under slightly uneven electrical field.Increasing the gap distance under extremely uneven electrical field will further aggravate the synergistic effect of gas mixtures.