Dynamic Characteristics of Electric Field Distribution at SF₆-insulator Interface in DC-GIL under Polarity Reversal

Surface charge accumulation during long-term operation is an important factor leading to surface flashover of insulators inside DC gas-insulated transmission lines (GILs). In this study, the effects of model scaling, model simplification, and prestressed time on the surface charge accumulation and electric field distribution characteristics of DC-GIL basin-type insulators during voltage polarity reversal are studied using finite-element simulation. The results show that, when the voltage polarity is reversed, owing to surface charge accumulation, the peak of the tangential field strength on the convex and concave surfaces of the insulator increases by more than 18% and shifts to the conductor side. Both the simplification and the scaling model affect the charge and electric field distribution on the insulator surface under polarity reversal. The peak tangential field strength of the convex surface increased by approximately 5%, 18%, and 27% after prestressing for 10 h, 100 h, and 1000 h, respectively, compared with that before the reversal. This investigation provides a useful guide for the design and optimization of DC-GIL basin-type insulators.