The Effects of SF₆-Cu Mixture on the Arc Characteristics in a Medium Voltage Puffer Gas Circuit Breaker due to Variation of Thermodynamic Properties and Transport Coefficients

In a gas circuit breaker, metal vapor resulting from electrode erosion is injected into the arc plasma. The arc then burns in a mixture of SF₆ and electrode vapor, which has properties significantly different from those of pure SF₆. Thermodynamic properties and transport coefficients of thermal plasmas formed in SF₆-copper vapor mixtures change as a function of temperature and pressure. The property that is mostly affected by the presence of copper is electrical conductivity, which is important in magnetohydrodynamic (MHD) analysis. In this study, the transport coefficients of SF₆ in the presence of 10 percent copper are considered as the basis of MHD simulation. Comparisons are made between the results during arc formation for pure SF₆ and SF₆-Cu mixture in a medium voltage (MV) circuit breaker. According to the transport coe±cients in°uenced by the SF₆-Cu mixture, the distribution of the electric potential, temperature, electromagnetic force density and current density of the arc column are presented and discussed. Also, the arc stability and pinch effect near current zero with 3-D simulation are investigated, which is advantageous to improving the efficiency of arc plasma simulation.