Simulation study of charge distribution characteristics on the surface of silicon nitride ceramics

Abstract Pure SF6 gas-insulated high-voltage DC through-wall casings use internal epoxy resin pillar insulators. During operation, temperature gradients and the long-term effects of the DC electric field lead to the accumulation of surface charge on the gas-solid insulation surface. This accumulation can easily trigger flashovers along the insulator’s gas-solid interface. The charge distribution characteristics of silicon nitride material in the DC electric field are less influenced by temperature gradients, making it a viable substitute for epoxy resin materials used in SF6 gas insulation support. In this paper, for the spatiotemporal variation of surface charge of epoxy resin and silicon nitride ceramic materials under a DC electric field, the material parameters are set based on the measured resistivity-temperature variation curves of epoxy and silicon nitride. The SF6 gas flow is considered to obtain a more accurate temperature distribution through the coupling of the heat flow field. The Schottky injection equation is introduced to take into account the influence of the surface charge accumulation process over a long period and to establish a more precise temperature distribution under the coupling of the DC electric field, the heat flow field, and the gas laminar flow field. The surface charge simulation model of epoxy and silicon nitride ceramics considering Schottky injection and bipolar carrier migration and transport model in SF6 under the multi-field coupling of the gas laminar flow field is established to analyze the dominant mechanism of the surface charge accumulation of epoxy and silicon nitride ceramics under the effect of the measured temperature gradient and to analyze the long-term change rule of the surface charge in the space and time.