Study of the arc interruption performance of SF₆-CO₂ mixtures as a substitute for SF₆

CO₂ attracts a lot of attention of researchers as a possible substitute for SF₆. The arc interruption capabilities of SF₆-CO₂ mixtures for different mixed ratios are investigated in this paper by carrying out tests with a 126 kV puffer gas circuit breaker prototype and calculations. Based on the measured arc voltage and current around current zero, the post-arc current characteristics and the thermal interruption properties are investigated for SF₆-CO₂ mixtures under different rise rate of the recovery voltage RRRV and di/dt before current zero. It is found that the interruption performance of SF₆-CO₂ increases greatly with increasing SF₆ concentration, and the critical RRRV and di/dt before current zero of SF₆-CO₂ mixtures for SF₆ content of 0, 20 and 50% are about 39, 45 and 70% of that of SF₆ respectively, at the short-circuit current of 10 kA. The pressure increment at current zero is found to have a great effect on the interruption of the short-circuit current. In addition, the pressure buildup in CO₂ is much lower than that in SF₆ for both no-load and loaded operations.