Study of the arc interruption performance of SF₆alternative gas in 35kV circuit breaker

SF6 gas is widely used in power equipment for its excellent arc extinguishing and insulation properties. However, SF6 is a strong greenhouse effect gas with a global warming potential (GWP) of 23, 500 times that of CO2. The research on SF6 environmental alternative gas has made great progress these years. C4F7N is considered the most likely gas to replace SF6 in the near future. Although C4F7N have the good arc extinguishing property, the arc extinguishing mechanism of it in 35kV circuit breaker is not clear. Because arc extinguishing is a complex physical and chemical process involving the interaction of gas flow fields, electromagnetic fields, and ablation the nozzle materials. It is difficult to quantitatively and directly evaluate the interruption performance of circuit breakers. In this paper, a method combining the simulation of the arcing process and the evaluation of the post-arc recovering ability for studying the characteristics of the arcing and post-arc recovering of the C4F7N/CO2 mixed gas is applied to 35kV circuit breaker. The temperature, pressure and airflow field characteristics during the arc burning process are compared and analyzed. Finally, through the post-arc recovering analysis, the post-arc currents at different rising rate of recovery voltage (RRRV) and zero-front current change rates (di/dt) are calculated, and the interruption performance of C4F7N/CO2 mixed gas and SF6 gas is obtained. By combining the Magnetohydrodynamics (MHD) analysis and the Mayr arc model the interruption processes for a 35kV circuit breaker filled with 5% C4F7N/CO2 at 0.8 MPa, as well as SF6 at 0.7 and 0.8 MPa, are investigated. It can provide a certain theoretical reference for the application of C4F7N/CO2 mixed gas in power equipment.