Influence of polymer structure on tree growth from a simulated tree channel

We have investigated the relationship between partial discharge (PD) in a simulated tree channel and tree growth from its tip. Structural weak-points inside polymer bulk was found to play very important roles in tree growth at low voltage range, especially when channel diameter is large (>30 μm). In this paper, influence of bulk structure on tree growth is discussed with annealed PP specimen. Inception voltage of tree growth in annealed specimen is higher than that in virgin specimen. The inception voltage increases with annealing temperature but independent of annealing time. Voltage dependences of total number of PD pulses required for tree growth and the shape-parameter of Weibull distribution are obtained. In virgin specimen, the shape-parameters m change from m⩽1 to m>1 with increasing applied voltage. However, in annealed specimen always m>1. The annealing effects on structure were analyzed using infrared spectrometer and X-ray diffractometer. Crystallinity and crystal structure of bulk are improved by the annealing process. It is suggested that a part of the amorphous region is recrystallized by the annealing process and structural weak-points are improved