Effects of Electric Field Nonuniformity on DC Positive Streamer Discharge of SF₆/N₂ Mixed Gas

The influencing mechanism of the electric field inhomogeneity on the microscopic streamer discharge in SF₆/N₂ is still unclear, which seriously limits the broad applications of electrical equipment filled with SF₆/N₂ gas. To investigate the impact of electric field nonuniformity on gas discharge, a streamer dc discharge simulation model with a semi-ellipsoidal-plate electrode with various discharge distances is constructed. The plasma parameters (particle density, space charge, reaction rate, streamer thickness, and velocity) evolution regularities of 20%SF6-80%N2 with different electric field inhomogeneity coefficients (f) are investigated. The results indicate that as the f increases, the collisional ionization reaction rate in the vicinity of the semi-ellipsoidal electrode increases during the corona stage of the discharge, leading to an improvement in the changing rate of the electrons and space charges in the region, which in turn enhances the electric field around the subsequent plasma channel. The enhanced electric field accelerates the gas ionization processes at the head of streamer, which promotes carrier mobility, improves the streamers' velocity and thickness, and causes a decrement in the macroscopic gas breakdown strength. The findings in this work reveal the influence of electric field uniformity on the streamer evolution characteristics in SF₆/N₂, which further accelerates the applications of SF₆/N₂ gas in offshore gas-insulated switchgear/gas-insulated line.