Electrical tree initiation according to the flow pattern in the EHV power cable insulation

Electrical treeing, regarded as the most likely mechanism of electrical breakdown in the solid dielectrics such as cable insulation, is with no doubt extremely fatal to the performance of the insulation. Treeing can be generally divided into two processes, initiation and propagation; they are quite different from each other in their occurrence, maintenance, process and appearance etc. Investigated in this paper is electrical tree initiation in the insulation layer of EHV power cables according to the flow pattern; the flux history of liquid polyethylene formed during the extrusion process. Electrical tree initiation voltage was measured using a newly developed electrode system with two opposing needles. Results were analyzed applying such a statistical method as Weibull distribution. 12 h, 3 h and 6 h direction areas corresponding to the positions in the flow pattern show dissimilarity of electrical tree initiation voltages distributed uniformly within the negligible range of 1.8%