Evolution of Surface Flashover Performance of Epoxy Resin in SF 6 Under Long-Term DC Voltage Application

High-voltage direct current (HVDC) transmission technology has become a focal point in power system research. However, its development is constrained by the issue of surface charge accumulation, which leads to a decline in flashover performance. To investigate this issue, an experimental platform for surface discharge was established in this study. The surface charge density and flashover voltage of samples under different voltage durations were systematically tested. Through the integration of numerical simulation models and microscopic surface morphology analysis using scanning electron microscopy (SEM), this paper systematically investigates the underlying mechanisms by which surface charge affects the surface flashover performance under long-term voltage application. The results show that surface charge accumulation, on the one hand, induces intensified electric field distortion, thereby reducing flashover voltage; on the other hand, under prolonged voltage application, plasma-induced surface modifications impede charge carrier migration, consequently enhancing flashover performance. For samples subjected to a voltage duration of 7 days, the effects of the two factors are comparable. However, as the voltage duration increases to 30 days, the influence of the former becomes significantly dominant, leading to a marked decline in flashover performance.