Simulation of the positive streamer propagation in SF6/N2 mixtures with different content of SF6

SF6/N2 gas mixture is considered as a practical alternative proposal of SF6 in GIL and GIS. Simulating the positive streamer propagations in different SF6/N2 mixtures assists in the optimization of SF6 ratio in SF6/N2 mixtures and the insulation design of GIL and GIS. This paper presents a fluid dynamic model for the positive streamer propagation in SF6/N2 mixtures. Based on this model, the positive streamer propagations in a 1 mm needle-plate gap in SF6/N2 mixtures with three different content of SF6 are simulated. Through the comparison of space net charge and chemical reaction rate, it is noted that there exists a negative space charge region in the streamer channel. With the increase of the ratio of SF6, the attachment of SF6 will be reinforced, thereby accelerating the accumulation of the negative space charge in the streamer channel. The increased negative space charge inhibits the ionization activity at the streamer head and leads to the increase of the critical ambient field sustaining the continuous propagation of the positive streamer. In SF6/N2 mixtures with high SF6 content, the decrease rate of the ionization activity at the streamer head may overwhelm the increase rate of the attachment rate in the streamer channel, indicating that the cease of the ionization activity is more likely to result in streamer decay in the SF6 mixtures with high SF6 content.