Experimental and Numerical Investigation of Surface Charge Accumulation Behavior Under DC Pre-Stress in SF6 Gas-Insulated Electrode Configuration

초록

With the expansion of renewable energy sources, the importance of voltage-source HVDC systems has been increasing, and ensuring the reliability of DC Gas-Insulated Switchgear (DC GIS) has become a critical issue. During DC GIS operation, impulse overvoltages caused by lightning strikes or circuit breaker operations may occur, necessitating insulation design that considers DC rated operating conditions. In particular, long-term DC voltage application can induce surface charge accumulation, leading to local electric field distortion and a consequent reduction in insulation strength. In this study, to investigate the effect of DC pre-stress conditions on insulation performance in a gas-electrode configuration without solid insulation, DC/Lightning Impulse (LI) superposed breakdown tests were conducted based on IEC 62271-5:2022. The breakdown voltages measured immediately after DC voltage application were compared with those obtained after 2 hours of DC pre-stressing. The results indicate that the difference in breakdown voltage due to DC pre-stress duration is not statistically significant. Furthermore, Finite Element Method (FEM) using COMSOL Multiphysics was performed to quantitatively analyze surface charge accumulation under DC voltage application. The simulation results show that surface charges rapidly increase during a short transient period immediately after voltage application and approach a steady-state distribution within several hundred milliseconds. This behavior is consistent with the experimental observation that the influence of DC pre-stress duration on insulation performance is limited.

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