Influence of impulse overvoltages and intermitting stationary voltages on the electrical treeing process in polyethylene

Electrical treeing inside a polyethylene insulation is influenced by many external stress parameters. Impulse overvoltages as well as intermittent stationary voltages are unavoidable during operation of polymer insulated devices. Therefore the influence of these stress parameters has to be investigated concerning their influence on the electrical treeing process. For this reason impulse overvoltages are applied to polyethylene samples at different phases of the electrical treeing. During bush-type treeing elongated and broadened channels are caused growing out of the bush structure. During branch-type treeing the influence is less critical. Intermittent stationary voltages are investigated in two series with different voltage terms. The more interruptions with a minimum duration of a few minutes appear, the more the erosion process is accelerated. The reason for this is the change in the electrical field inside the tree channels leading to an enlarged withstand voltage of the gas inside the channels after an interruption. The following discharges with higher amounts of charge cause the accelerated growth of the channels