Time and Space Transition of DC Electric Field Distribution Based on Emerging Field by Accumulated Charge in Gas-solid Composite Insulation Structure

In this study we investigate the time and space transition characteristics of DC electric field in SF6 gas from the initial state DC-on to final DC steady-state in gas-solid composite insulation systems. Using a simple rod-electrode configuration and actual insulating epoxy-spacer model, the electric field distributions of the epoxy-spacer in SF6 gas and time constant T of electric field formation from DC-on to DC steady-state are calculated based on the electric conduction characteristics. In addition, the emerging electric field distributions due to accumulated charge on solid insulator surface are introduced to elucidate the time transition process of electric field stress in the gap between HV conductor and GND. As a result, we quantitatively clarify that the time constant T of electric field formation are highly dependent on the non-uniform factor η and location of the gap space in the electrode configuration under non-uniform DC electric field. The locations with higher electric field stress in the gap space have the shorter time constant T. In addition, the time transition process of electric field stress in SF6 gas depends on the gap space and the location of maximum electric field change during time transition. Especially, we clarify that the highest electric field stress in SF6 gas may emerge in actual GIS structure based on the time transition process of emerging electric field due to accumulated charge.