SF6, which is currently widely used in gas-insulated power transmission equipment, is a greenhouse gas with a very strong greenhouse effect. Therefore, developing environmentally friendly gas insulation equipment to gradually reduce the use of SF6 has become a hot research topic. As the most potential alternative gas, C4F7N is of great significance to study the electrical characteristics of the medium-voltage switching field to promote the green development of the power industry. Based on

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... physical field coupling to construct the 40.5 kV circuit breaker mode, this paper uses C4F7N/CO2 mixed gas to compare and study the dynamic characteristics of a C4F7N/CO2 mixed gas circuit breaker when breaking the short-circuit current and the dielectric recovery strength with no-load breaking, as well as to evaluate the electrical performance of C4F7N mixed gas in a 40.5 kV breaker with the gas breakdown criterion. The results show that mixing O2 in a high current can improve the breaking performance of an environmental protection circuit breaker and increasing the C4F7N mass fraction can enhance the dielectric recovery strength of the environmentally friendly circuit breaker. Considering the overall performance of the gas, the 5%C4F7N/90% CO2/5%O2 mixed gas has some alternative potential.