Effect of additives on DC treeing breakdown in polyethylene under divergent field

The effect of additives on DC treeing breakdown phenomena and the space charge formation near the tip of a needle electrode inserted into polymeric material were studied under various conditions. Ionomer-blended low density polyethylene (LDPE), polyamide-blended LPDE, and cross-linked samples which include acetophenone were investigated. The DC tree inception voltage for the positive point is almost independent of ionomer content. But the DC tree inception voltage for the negative point which is greater than that for the positive one decreases with an increase of ionomer or polyamide content. The extension length of the polarity-reversal tree which occurs on the application of impulse voltage of inverse polarity after the DC prestress decreases with an increase of ionomer or polyamide content. On the other hand, the DC tree inception voltage of the crosslinked samples with acetophenone is greatly higher than that of blended LDPE. Furthermore, the extension length of the polarity-reversal tree of crosslinked samples with acetophenone is longer than that of blended LDPE. From these results, it is suggested that ionomer or polyamide which is blended into LDPE improves the DC tree resistance, and that acetophenone in crosslinked samples enhances the amount of accumulated space charge