Time dependence of AC flashover characteristics for particle-initiated breakdown in GIS

The AC flashover characteristics for wire-particle-initiated breakdown and its time dependence were studied in a realistic 362 kV SF ₆ gas-insulated bus duct. The voltage leading to breakdown after two hours was calculated from studies of the time to breakdown at different voltages. The calculations were made for different pressures and compared with the experimentally obtained two-hour withstand voltage. The influence that the long-term exposure to voltage has on the particle was studied, including both the particle deformation and the impact that the deformation has on the particle movement pattern and the AC flashover characteristic. It was found that the deformation taking place at the ends of the wire, depends on the wire material and diameter and on the duration of the voltage application. In some cases it plays a decisive role in the time dependence of the AC flashover characteristics