Research On The Arc Interruption And Insulation Performance Of Environmentally Friendly Insulating Gas CF₃I

Recently,environmentally friendly gas CF₃I is regarded as one of the most potential replacement gas because of its good electric and physical properties.Due to the lack of fully understanding on the arc interruption capability and insulation property of CF₃I,as well as the knowledge of arc interruption process,we identify the mechanism responsible for different arc extinguishing performances in CO₂,air and SF₆ gases basing on computer simulation to evaluate the arc interruption capability of CF₃I gas,and compare its insulation properties before and after arc using gas breakdown test and Boltzmann equation method.Firstly,we summarize the theory framework of gas-blast arc computation model and select proper algorithms to simulate relative physical processes including electric and magnetic field,turbulence and radiation.Through comparison with measured data,thermodynamic and transport parameters of CF₃I gas in the condition of high temperature and pressure are calibrated and summarized in order to be used in arc simulation.We also introduce the establishing and calculating procedures in the solver ANSYS Fluent.Based on the above theory,we build up DC?direct current?steady and AC?alter current?transient nozzle arc model respectively with working gas of CO₂,air and SF₆ to study heat recovery capability of different gases and physical property determining gas interruption capability.By comparing to measured data including radial arc temperature and limited RRRV?rising rate of recovery current?,we calibrate and summarize radiation and turbulence coefficients in the three gas arc models.Before current zero,SF₆ gas has low value of?C_p property without peaks above 4000 K leading to strong process of radial conductivity and radial convection in its arc,while CO₂ and air have high values of?h properties leading to strong process of axial convection.At very near current zero,SF₆ arc with strong radial convection process inside,will lose energy more effetely and be extinguished more easily,so SF₆ has better arc interruption performance than other gases.Besides,we set up a simple theory model to obtain a?property near and after current zero to estimate reducing rate of electric conductivity during thermal recovery.It is concluded that an insulating gas with strong arc interruption capability has a?C_p property with no peaks above 4000 K and as high as possible value below 4000 K,as well as high?property.Based on the obtained guidance of arc interruption capability,we analysis relative material parameters of environmentally friendly gas CF₃I and study the arc extinguishing performance of CF₃I gas.We also conduct gas interruption test in switchgear and adopt chromatograph and mass spectroscopy to analyze the byproducts after arc.Seen from its?C_p property and?property,the arc interruption capability of CF₃I gas is slightly weaker than that of SF₆,and much stronger than that of CO₂ and air.After successful interruption,the decomposed ratio is only 3.3%and the main byproduct CF₄ and C₂F₆,have good toxic and environmental property.In the premier of successful interruption and proper adsorbent for solid byproduct,the decomposition problem will not affect the application of CF₃I in switchgear.Besides,we measure the breakdown voltages of pure CF₃I and CF₃I/CO₂ gas mixtures in non-uniform electric field and compare the electron swarm and transport parameters.In needle-plate geometry,the breakdown strength of pure CF₃I is good at low pressure and need to be improved at high pressure by adding buffer gas to weaken hump effect.The computing result of Boltzmann equations shows that the discharge properties after successful interruption approaches that of the original gas,but falles down to 56%of that of the original after arc reignition.Thus,some buffer gas need to be added to CF₃I applying in switchgear apparatus from the view of insulation strength and liquefaction temperature.The study in the present paper provides basic criterion for gas interruption capability and forms the theoretical foundation of the application of CF₃I in switchgear.