Surface Charge Accumulation Behavior on GIL Spacer Under DC Voltages in SF 6 /N 2 Mixtures

The accumulated charge on insulator surface is an important factor to trigger surface flashover. A surface charge experimental setup as well as measurement system under high gas pressure is built. An active electrostatic probe (Trek 3455ET, Model 341B) is used to measure surface potential distribution on a downsized cone-type spacer in SF 6 /N 2 mixtures of different pressure under DC voltage. The actual charge density distribution is computed by the charge inverse algorithm, which considers the impact of the probe. The surface charge distribution shows similar shape at different pressure, including the homo-charges presenting a symmetrical distribution and a streak-like distribution. For the home-charges presenting a symmetrical distribution, they come from surface conductivity. For the streak-like distribution, they are located between central and grounded electrode. These charges come from the ionization of SF 6 due to the local electrical field concentrated.