Space-charge-stabilization in SF6

The insulation level of gas insulated switchgear (GIS) may be influenced by defects like needle-shaped protrusions. In the case of slowly rising impulse voltages and AC stress it is enhanced by corona-stabilization. This phenomena caused by the ion drift during streamer development and the resulting space-charge is investigated. We present new experimental results about this phenomena. The paths of the breakdown channels across a point/plane gap have been recorded. The tip geometries of the protrusion, gas pressures and steepness of the applied test voltages have been varied during the experiments. Based on these results the fundamental idea of a new simulation model is presented. By electrostatic field calculations the time dependent growth of the streamer and the movement of the positive SF₆-ions have been calculated for the applied geometries. It is assumed that space-charge stabilization only occurs if the velocity of the streamer growth is lower than the drift velocity of the positive ions and the ions move in front of the streamer region and reduce the electric field within the streamer