Compositions of SF6 - H2O Decaying Arc at a Temperature Range of 1000–12000 K

Abstract

SF6 has been widely used as insulating and arc-extinguishing medium in power equipment. But under arc discharges, lower fluorides of sulfur (like SF5, SF4and SF3) generated by the dissociations of SF6will react with unavoidable atoms (like O and H) released from trace impurities of moisture to form corrosive byproducts such as SOF2, SO2F2, SOF4and so on. These byproducts will reduce the insulating and arc-quenching capacity of SF6-insulated power equipment, so it is necessary to study the compositions of decaying SF6arc plasma in the presence of H2O. In this paper, both non-chemical and non-thermodynamic equilibriums are taken into consideration employing chemical kinetic model. The elementary reactions of SF6with H2O are determined by density functional theory and the rate coefficients are computed with transition state theory. Then we calculated the temperature-varying molar fractions of main byproducts SOF2, SO2F2and SOF4under different contents of H2O. We also analyzed the dominant reactions in different selected temperature ranges. This work can lay a theoretical basis for insulating condition monitoring and diagnosis of SF6-insulated power equipment based on characteristic decomposition products.