Simulation Study on Charge Distribution Characteristics of Gas–Solid Interface Based on Improved Saturation Current Density Method

Free charge accumulation on the surface of solid insulation under direct current (DC) voltage distorts the electric field distribution on the insulator’s surface, affecting discharge behavior, such as creeping flashover. Numerous experiments and simulation studies have been conducted by scholars worldwide. Current research shows that there are three primary sources of surface charge on gas–solid insulation: bulk current on the solid side, ionic current on the gas side, and surface current on the gas–solid interface. In GIS, GIL, and other power equipment, the field strength of each critical component is low, and no partial discharge occurs during normal operation; hence, the source of gas-side charge is mainly the weak ionization of gas molecules. However, oscillating solutions occur in the discrete form of the convection-diffusion equation in the gas field, which leads to non-convergence of iteration. This study proposes, for the first time, an improved saturated current density calculation method for charge accumulation at the gas–solid interface of insulators. The surface charge accumulation characteristics of post-insulators in air under DC voltage at normal temperature and pressure are measured. The rationality and accuracy of the simulation calculation method are verified by comparing and analyzing the experimental results. The results indicate that there are two different polarity potential peaks and one homopolar potential peak on the surface of the post-insulator under DC voltage. The position of the potential peak remains unchanged with the increase in voltage application time. At the lower part of the sample, the gas-side current is less than the solid-side current density, resulting in the accumulation of negative charges on the surface. In contrast, at the upper part of the sample, the gas-side current exceeds the solid-side current density, and the surface also accumulates negative charges. In the middle part of the sample, the insulator surface area gathers positive charges, driven by the solid-side charge. This research can provide theoretical support for the design of DC transmission equipment.