| Summary: | SF<sub>6</sub>, 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 SF<sub>6</sub> has become a hot research topic. As the most potential alternative gas, C<sub>4</sub>F<sub>7</sub>N 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 multi-physical field coupling to construct the 40.5 kV circuit breaker mode, this paper uses C<sub>4</sub>F<sub>7</sub>N/CO<sub>2</sub> mixed gas to compare and study the dynamic characteristics of a C<sub>4</sub>F<sub>7</sub>N/CO<sub>2</sub> 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 C<sub>4</sub>F<sub>7</sub>N mixed gas in a 40.5 kV breaker with the gas breakdown criterion. The results show that mixing O<sub>2</sub> in a high current can improve the breaking performance of an environmental protection circuit breaker and increasing the C<sub>4</sub>F<sub>7</sub>N mass fraction can enhance the dielectric recovery strength of the environmentally friendly circuit breaker. Considering the overall performance of the gas, the 5%C<sub>4</sub>F<sub>7</sub>N/90% CO<sub>2</sub>/5%O<sub>2</sub> mixed gas has some alternative potential.
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