Research On The Arc Microscopic Characteristics Of SF₆ Gas Mixtures

With the continuous development of the national economy,the demand for electricity continues to increase steadily.In order to meet the demand for electricity,the increase of transmission capacity,the development of power transmission and transformation system and related technical equipment are of great significance.SF₆ circuit breaker is the most important protection equipment in electric power system.It is widely used in power plants,substations,switching stations and electricity lines.However,due to its high greenhouse effect,SF₆ has been listed as one of the 6 restricted gases used.Therefore,it is significant to look for new gases which insulation performance is similar to SF6 and have low greenhouse effect index.N₂ and CO₂,as the main components of air,easy to extract,are the preferred objects for SF₆ mixture research.The core problem of SF₆ circuit breaker is the interruption problem,that is,the arc problem.The study of the generation,development,evolution and the time-varying law of microscopic particle density of mixed gas arc and the study of the main factors affecting the energy and interruption of the mixed gas arc are of great significance.At present,the research on the micro mechanism of the arc is mainly focused on the steady state plasma mathematical model theory simulation research or experimental research on high-speed photography.The research on the microscopic dynamic process of before-arc is relatively few.Therefore,from the microscopic perspective,considering the collision of charged particles,the formation process of SF₆/N₂ and SF₆/CO₂ mixtures arc in uniform electric field and non-uniform field,the change of parameters and the influence of gas composition on the characteristics of the arc are studied in this thesis.The key problems of the formation and extinction of SF₆ mixtures arc are further explored from microcosmic aspect.In this thesis,an arc mathematical model describing the non-equilibrium process is established on the basis of the study on the physical process of hybrid gas arc,which is based on gas dynamics,including electron,positive and negative drift diffusion equation,coupling electric field Poisson equation.The effect of space charge on electric field caused by collision reaction between particles is also considered.A two-dimensional axisymmetric calculation model is established for the uniform plate electrode and the actual structure of the non-uniform SF₆ circuit breaker arc chamber.The boundary conditions were determined,and the arc forming process of SF₆/N₂and SF₆/CO₂ mixtures under the action of two kinds of electric fields is simulated and analyzed.The electron density,electric field strength,average electron energy and other micro parameters of the two kinds of mixtures are compared and analyzed.The influence of SF₆/N₂and SF₆/CO₂ mixtures on the arc characteristics is verified.The simulation results show the microscopic explanation of the arc development law of SF₆/N₂ and SF₆/CO₂ mixtures under uniform and non-uniform field and the influence of variable factors,which provides a theoretical reference for the research of SF₆ alternative gas arc characteristics.