Theoretical study on gas decomposition mechanism of SF6 by quantum chemical calculation

Abstract

Sulfur hexafluoride has excellent insulating and arc-suppression properties, and is widely used in gas-insulated switchgear. Under high voltage discharge condition, SF6 decomposes into various by-products according to discharge scenarios. The formation mechanism of decomposition products is so far not clear. For most of the studies, experimental measurements are used to speculate the reaction mechanism, and those research is postulated with great arbitrariness. Quantum chemical calculation by using high precision simulation theory is a very effective method to reveal the microcosmic mechanism of complex chemical reaction. Therefore, in this paper, we used high level quantum chemical method (B3P86/6-31G∗∗) to study the mechanism of decomposition reaction and products, in presence of trace air or H2O. The decomposition products include SO2, H2S, and HF. For each reaction product, we provide a detailed generation pathway, including the data and energy structure of reaction intermediates and transition states. The simulation results can explain the experimental results accurately, and provide new understanding and support for the judgment of the discharge reaction state and subsequent electrical aging. These results are very helpful to build SF6/H2O/O2 reaction model, and indicate the electrical aging process from microcosmic angle.