Tree discharge in extended chain crystal polyethylene

Extended chain crystal (ECC) polyethylene exhibits some unique properties. It is possible to make transparent highly crystallized polyethylene in the ECC phase. Electrical treeing was investigated using a needle to plate electrode system under an application of lightning impulse voltage. The propagation direction of trees was strongly influenced by the orientation. When the orientation of ECC polyethylene was normal to the electric field, the trees propagated not along the electric field but along the direction of the orientation. The tree growth was observed using a high-speed image converter camera. The formation of tree channels was a very rapid phenomenon within 1 /spl mu/s. The discharge current accompanying the trees consisted of two kinds. A large current pulse, which occurred just after voltage application, appeared to be a combination of injection current and charging current. After this large pulse, small current pulses appeared intermittently in the wave tail of the applied voltage. It is thought that these small current pulses are attributable to the back discharge due to the accumulated charges.