Influence of partial discharges on the development of electrical treeing in polyethylene insulated cables

This paper presents the results of needle tests conducted on 15 kV polyethylene insulated cables. The tests were performed for metal needle electrodes as well as for gas point electrodes (pinholes). The differences between the shape and the growth rate of electrical trees in both cases are presented. The development of treeing until the point of insulation breakdown was observed using an optical arrangement. Simultaneously, measurements of partial discharges were performed. The results of these investigations indicated clear correlation of the growth rate of electrical trees to the apparent charge.