Unraveling Electric-field Dependent Surface Charge Accumulation Mechanisms of Insulator in SF 6 /N 2

Surface charge accumulation at the gas-solid interface induces surface flashover for long-term operational DC GIS systems, which represents a critical failure form of insulators. However, owing to the absence of a charge accumulation equation for actual insulator surface protrusions, the experimental results are inconsistent with simulation data by the model, failing to adequately reveal the surface charge accumulation mechanism. This work develops a surface ionization equation for insulators and integrates it into the surface charge accumulation model to analyze the influence of micro-protrusions on charge accumulation characteristics. Unraveling the principles of surface charge accumulation under different electric fields through both experimental and simulation approaches. Experimental results demonstrate that when the electric field improves, surface charge accumulation shifts from homopolar to heteropolar, and the shift point moves toward higher electric fields as the concentrations of SF6and Al2O3increase. Simulation results indicate that an enhanced gas collision ionization coefficient promotes the surface ionization process, consequently reducing the charge polarity shift voltage point as the SF6decreases. The solid bulk conductivity improves, the bulk current density enhances, resulting in higher charge polarity shift voltage point with increased Al2O3particle concentration. This paper reveals the “gas phase-solid phase” competition dominated mechanism of insulator surface charge accumulation under different electric fields. This mechanism provides theoretical support for improving the performance modification strategies for insulation components.