Characteristics of discharges inside simulated tree channels under impulse voltage

The authors attempt to characterise the electrical discharges initiated in hollow filaments of small diameter in low-density polyethylene. This study is related to electrical treeing, a pre-breakdown phenomenon in certain polymers submitted to high electrical stresses. A positive single pulse voltage was applied to a channel prepared in a polyethylene specimen. The channel diameter ranges from 1 mm to 13 mu m and the gap from 1 to 5 mm. The characteristics of the discharges growing in the channels were recorded and compared with free air discharges under the same conditions. It is shown that the channel walls disturb the discharge below a critical value of the ratio between the channel diameter ( Phi ) and the gap (d). A quicker heating of the gas is assumed to explain the behaviour of these confined volumes.