Numerical simulation of streamer discharge development processes with multi-component SF6 mixed gas

Abstract

In recent years, more stringent environmental protection requirements have led to increasingly higher voltage power equipment that adopt SF6 mixed gas as an insulation medium. In this paper, the streamer development in SF6 mixed gas and the distribution of each gas component were studied over time. Thus, a discharge model of the needle plate electrode with SF6 mixed gas was established. The hydrodynamic model for SF6 mixed gas discharge in uneven electric fields was created by coupling the Boltzmann drift-diffusion equation and Poisson's equation. The influence of different factors, such as the applied voltage, gas mixture ratio, and electrode spacing, on the streamer discharge of SF6/N2 mixed gas, and the influence of the type of mixed gas (air and CO2) combined with SF6 on the streamer development process were studied. The simulation results showed that the higher SF6 content in the mixed gas made breakdown more difficult, and a higher pressure led to a more concentrated streamer. Comparing and analyzing the discharge processes under different SF6 mixed gases (SF6/CO2, SF6/air, and SF6/N2) showed that the streamer for the SF6/CO2 mixture took longer to develop toward the plate electrode with a more difficult breakdown. The presented simulation results provide a microscopic interpretation for the needle-plate discharge defects that appear in power equipment that utilize SF6 mixed gas.