Research On Micro And Macro Characteristics Of CF₃I/CO₂ Mixed Gas Arc

With the development of national economy and the increasing of the demand for power,the requirements for breaking capacity of the switching equipment are also gradually increased.SF₆ is widely used in high voltage switches because of its excellent arc performance.However,SF₆ gas has serious greenhouse effect and is not conducive to environmental protection.In order to reduce SF₆ emissions,domestic and foreign scholars have done a lot of research to find suitable alternative SF₆ gas.CF₃I（trifluoroiodomethane）,an environment-friendly insulating gas,is considered as one of the gases with potential to replace SF₆ because of its excellent arc and physicochemical properties.The liquefaction temperature of CF₃I gas is higher than that of SF₆ gas,but the application range of pure CF₃I gas is small,and mixed buffer gas is often used to reduce the liquefaction temperature.Therefore,CF₃I/CO₂ mixture gas is studied in this thesis from micro and macro perspectives to analyze its arc characteristics,and explore the feasibility of its replacement of SF₆ gas.The research status of SF₆ hybrid buffer gas and new environment-friendly alternative gas are introduced first in this thesis,and the feasibility of CF₃I/CO₂ hybrid gas to replace SF₆ gas is proposed.The research status of arc model is introduced,and the gas dynamics theory of micro plasma development and the local thermodynamics theory of macro steady arc are expounded to study the micro and macro arc models used in CF₃I/CO₂ hybrid gas research in this thesis.Based on the gas dynamics equation,a two-dimensional axisymmetric plate electrode model for CF₃I/CO₂ front-arc process at a small space-time scale is established.The formation process of CF₃I/CO₂ mixed gas plasma breaking arc is studied from the micro level.The variation of electron density,average electron energy,anion number density formed by adsorption and sheath thickness are analyzed.The influence of mixing ratio on the parameters of CF₃I/CO₂ mixture gas is also discussed,and the possibility of replacing SF₆ gas is analyzed.Parameters such as particle number density and electron mobility are extracted to calculate the conductivity of sheath area,which provided initial data for macroscopic arc model calculation.Based on the local thermodynamics theory and considering the turbulence effect,the sheath parameters calculated by micro-simulation are coupled.The arc model of two-dimensional axisymmetric arc extinguishing chamber is established to explore the differences of temperature distribution,velocity distribution and arc conductance between CF₃I/CO₂ mixture gas and SF₆gas.It is further analyzed from gas physical property parameters and energy transport equilibrium relationship.On this basis,the arc characteristics of CF₃I/CO₂ mixture gas under the influence of mixing ratio and different air pressure are studied.The results show that the mixture of 30%CF₃I/70%CO₂ has a good possibility of replacing SF₆ gas,which provides a theoretical basis for the development of a new SF₆ gas circuit breaker.