Research On Breaking Performance Of E Nvironment-friendly C₄F₇N/CO₂ Mixture Gas Circuit Breaker

SF₆ gas has been widely used in electrical equipment as an arc extinguishing and insulating medium in the 1960s due to its excellent insulation and arc extinguishing properties.However,as a strong greenhouse gas,it has a high environmental pressure.In order to reduce the use of SF₆gas and emissions,scholars at home and abroad have carried out many studies,including reducing the size of equipment,improving gas treatment and recovery methods,using SF₆ mixed gas,etc.,but the most effective means is screening,research or development Alternative gas.At present,the perfluoroisobutyronitrile?C₄F₇N?developed by 3M Company performs well in environmental protection and electrical strength,which has aroused great interest from researchers.Because of its high liquefaction temperature,it is difficult to apply in high cold areas,so it is often mixed with CO₂,a conventional gas.In recent years,the research of C₄F₇N/CO₂mixed gas by domestic and foreign academic research teams has focused on physical and chemical characteristics,insulation characteristics and discharge decomposition characteristics,but the research on the breaking performance of its application to circuit breakers is very limited.In order to better evaluate the breaking performance of C₄F₇N/CO₂ mixed gas,this paper uses a40.5kV circuit breaker as a prototype to carry out the C₄F₇N/CO₂ mixed gas circuit breaker short-circuit breaking characteristics simulation and experimental study of arc breaking characteristics.The main work is as follows:?1?Based on fluid dynamics theory and Maxwell's equations,a two-dimensional magnetohydrodynamic?MHD?mathematical model is established,a standard turbulence model is used to consider the effect of arc turbulence,an arc radiation model is established according to the net radiation coefficient method,and a user-defined function?UDF?is used Complete physical property parameter input,movement speed call and specific physical quantity output.Establish a complete multiphysics simulation model of C₄F₇N/CO₂ mixed gas circuit breaker.According to the thermodynamic properties of the mixed gas,the gas pressure characteristics,air flow characteristics and insulation characteristics of the C₄F₇N/CO₂ mixed gas circuit breaker during the breaking process were analyzed,and the effects of the C₄F₇N/CO₂ content in the mixed gas and the pressure of the arc extinguishing chamber on temperature,pressure,particle density and arc characteristics.?2?According to the streamer theory and pederson breakdown criterion,establish a medium recovery mathematical model,combined with the calculation results of the electric field and airflow field of the C₄F₇N/CO₂ mixed gas circuit breaker,calculate the breakdown voltage distribution during the circuit breaker breaking process,and obtain different gases Under the conditions of C₄F₇N/CO₂ mixed gas circuit breaker dielectric recovery characteristic curve.Comprehensive analysis of the numerical calculation results gives the optimal ratio and charging scheme of the C₄F₇N/CO₂ mixed gas circuit breaker's breaking performance.?3?An experimental circuit is built to study the arc breaking characteristics of C₄F₇N/CO₂mixed gas.The circuit breaker is filled with different pressure pure SF₆ and C₄F₇N/CO₂ mixed gas with different mixing ratios to conduct circuit breaker breaking experiments.The arc characteristics of SF₆ and C₄F₇N/CO₂ mixed gases are analyzed and compared,and the arc emission power and time constant under different gas conditions are solved.The Matlab/Simulink platform was used to establish the short-circuit current breaking simulation circuit,and then the corresponding back-arc current characteristics under different gas conditions were studied.