Numerical simulation of the microscopic discharge processes in SF₆/N₂ mixtures: Effects of gas composition, voltage, and electric field distribution

Abstract

To investigate the corona discharge mechanism of SF₆/N₂ gas mixtures under non-uniform electric fields, a two-dimensional fluid model was developed using a needle-plate electrode configuration. The model couples the drift-diffusion equations of electrons and ions with the Poisson equation and includes key processes such as electron impact ionization, attachment, recombination, and photoionization. Electron transport parameters for various SF₆/N₂ ratios were obtained by solving the Boltzmann equation, and the model was validated against classical benchmarks. The spatiotemporal evolution of charged particle densities and the electric field during negative corona discharge was analyzed, examining the effects of applied voltage, SF₆ mixing ratio, and needle-plate gap. Results show that discharge initiates at the needle tip, where electron density concentrates, and propagates toward the plate as the streamer develops. Space charge accumulation distorts the local electric field, enhancing ionization at the streamer head. Higher applied voltage increases both the streamer-head field strength and propagation velocity, promoting transition toward breakdown. Increasing SF₆ content strengthens electron attachment, reducing electron density and axial electric field, thereby suppressing streamer growth and improving insulation. Reducing the gap under the same voltage raises the maximum field strength, facilitating discharge. These findings provide theoretical guidance for applying environmentally friendly SF₆/N₂ mixtures in gas-insulated power equipment.