Transient nozzle pressure characteristics of SF₆-CO₂ and SF₆-CF₄ circuit breaker

Due to their stable physicochemical property and good arc-quenching capability, both CO₂ and CF₄ gases attract a lot of attention of researchers as a possible substitute for SF₆. The transient nozzle pressure during the arc interruption process is necessary for the arc-interrupting properties and the optimization design of circuit breakers.We measured and analyzed the gas pressure variations at the upstream of PTFE nozzle in SF₆-CO₂ and SF₆-CF₄ mixtures for different mixed ratios by carrying out tests with a 126 kV puffer gas circuit breaker prototype. It is found that both the peak value of the gas pressure increment Δp_peak and the gas pressure increment at current zero Δp_CZ in SF₆-CF₄ mixture are clearly higher than those in SF₆-CO₂, which indicates the stronger gas blowing effect of SF₆-CF₄ mixture. With the increase of SF₆ concentration, the Δp_peak in both gas mixtures of SF₆ and the Δp_CZ in SF₆-CO₂ increase obviously, while the Δp_CZ in SF₆-CF₄ varies slightly. In addition, the establishment of outlet pressure plays an important role in the thermal interrupting capability of a circuit breaker.