Kinetic analysis of the effect of O2 on SF6 over-thermal decomposition

Partial over-thermal fault (POF) may occur during operation of SF6 gas insulated equipment, which will cause SF6 to decompose and threaten the safety of equipment and stable operation of power grid. The decomposition of SF6 is closely related to the residual O2 inside the equipment. The decomposition mechanism of SF6 under the action of O2 needs to be studied in depth but there is still a lack of a force field to describe it. This paper first establishes a reactive force field (ReaxFF) that can describe the microscopic reaction process of SF6 and O2 coexisting systems. Using the force field, a series of molecular dynamics (MD) simulations are performed to explore the effect of O2 on the over-thermal decomposition of SF6. First, the main chemical reactions affecting the formation of the characteristic products were obtained. Second, the decomposition process of SF6 and O2 with different proportions is studied, and the kinetic process of reactions are observed, which simulates the changes in quantity of the major products including SOF4, SOF3, SOF2, SO2F2, SOF and SO2. In addition, transition state theory is used to study the changes in energy and molecular structure during the reaction. Synthesizing the simulation results, the mechanism of O2 on the over-thermal decomposition of SF6 is analysed. The work advances understanding the mechanism of over-thermal failure of gas insulated equipment.