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The present paper describes numerical thermofluid simulation results of SF 6 , Ar, and Ar/SF 6 arcs in a nozzle space at atmospheric pressure on the assumption of local thermodynamic equilibrium (LTE) condition. It is crucial to investigate fundamentals on arc extinction phenomena by numerical simulation approach as well as experimental approach. Two-dimensional temperature distributions in SF 6 , Ar, Ar/SF 6 gas-blast arcs were calculated in a steady state at a direct current of 50 A. Furthermore, transient temperature distributions in these arcs were computed under free recovery condition for a fundamental study. We investigated dependences of the gas mixture ratio of SF 6 to Ar and the gas flow velocity on the arc temperature and the arc voltage. The calculated arc voltage in the steady state and the transition of electron density under free recovery condition were compared with those obtained by laser Thomson scattering method in our experiments. As a result, the increasing admixture ratio of SF 6 to Ar and the increasing gas flow velocity shrinks the arc plasma around nozzle throat inlet, leading to the higher arc resistance. Under free recovery condition, the arc plasma decay more rapidly there. Comparison in electron density shows the similar dependence on SF 6 and Ar, while there is still some difference in the absolute value of electron density between the calculation results and experimental results.

This paper presents the arc quenching abilities of various gases studied using a power semiconductor switching technique. This technique uses an insulated gate bi-polar transistor (IGBT) for current injection and voltage application to the arc plasma. Using this technique, arcs under a free recovery condition from a 50 A steady state condition were investigated in SF 6 , CO 2 , O 2 , N 2 , air and Ar gas flows. Furthermore, at a specified timing, high of voltage about 1.1 kV and 1.7 kV/µs was applied by the IGBT to residual decaying arcs to elucidate the arc re-ignition processes and recovery properties. These systematic experiments further enabled us to estimate the interruption probability versus the voltage application timing. From these results, the voltage application timing of 50% successful interruption was estimated for various gases. The results showed a direct relation to the interruption capabilities of the respective gases. These results were then compared to electron density measurement results and numerical simulation results to confirm their validity. All data obtained from experiments and simulation are expected to be useful to elucidate the arc quenching physics and also for the practical application of arc quenching phenomena.