Electrical Tree Initiation and Growth in LDPE Under Negative DC Fields

Electrical tree initiation and growth in low-density polyethylene (LDPE) with a needle-plane geometry under negative DC fields was investigated in this work. Many differences have been found between the cases of the needle being energized positive (positive DC fields) and those in which the needle is negative (negative DC fields). Tree initiation in the latter could occur under a wider range of voltage magnitudes and had a shorter initiation length. Negative trees also tended to initiate more quickly than positive trees, and considerable length propagation was observed to immediately follow the initiation. Furthermore, there were differences in partial discharge signals between the two polarities. These distinctions are thought to be caused by the differences in nature between hole injection and electron injection and the subsequent space charge accumulation in the polymer around the needle tip.