Effects of DC Prestressing on Tree Initiation in Polyethylene with and without Needle-Shaped Void

The effects of dc prestressing on tree-initiation in polyethylene wit needle-shaped voids have been investigated so that a comparison between specimens with and without voids could be made. When the polarity of the pulse is the same as the dc voltage, the effect of dc prestressing is negligible on the 50%-tree-initiation voltage. On the other hand, the opposite polarity gives a significant effect. For the dc prestressing test with the opposite polarity, the effect of the dc prestressing disappears in 2000 s for the specimen with void, and 4000 s for the specimen without void, using -16 kV dc prestressing voltage. In positive dc prestressing tests, the effect of the dc prestressing disappears in 5000 s under 16 kV dc voltage for the specimen without void. For the specimen with void, however, the recovery time is only 100 s.