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

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.