Numerical simulation of the positive streamer propagation and chemical reactions in SF6/N2 mixtures under non-uniform field

SF6/N2 mixtures is considered as a practical alternative proposal of SF6 in GIS and GIL. Simulating particle transportations and chemical reactions during the positive streamer propagation in SF6/N2 mixtures assists in the insulation performance optimization of SF6/N2 mixtures. This paper presents a fluid dynamic model coupled with the chemical reaction system for the positive streamer propagation in SF6/N2 mixtures. The Townsend coefficients of the 20%SF6/80%N2 mixture derived from the proposed chemical reaction system are in accordance with the measurement results. Based on this model, the propagation of the positive streamer in a 1 mm needle-plate gap in the 20%SF6/80%N2 mixture is simulated. Simulated results indicate that there exists a negative space charge region in the streamer channel. It can be attributed to the increasing attachment rates of SF6 yielding SF5⁻ and SF6⁻, and the reduction of the ionization rates of N2 and SF6 in the streamer channel. Besides, it is noted that the ionization activities of N2 and SF6 at the streamer head are equally important to support the continuous propagation of the positive streamer. The ionization of N2 in the streamer channel serves as an important factor to supply electrons and avoid the accumulation of the negative space charge.