Effect of additives and pre-stressing on tree inhibition

The effect of additives on treeing initiation was studied in LDPE (low-density polyethylene) and XLPE (cross-linked polyethylene) under various oxygen concentrations. The additive effect on AC tree suppression was found to be a function of oxygen concentration absorbed in PE and remarkable in the range from 1 p.p.m. to 10%. This suggests that the additive works as a radical stabilizer to suppress the tree. In contrast with the case of an AC tree, the additives had little effect on positive impulse tree initiation. But they decrease the negative impulse tree initiation voltage. On the other hand, AC prestressing suppresses tree initiation by AC ramp voltage. After prestressing, it was observed that additive molecules migrate to concentrate around the tip of the needle electrode. This probably causes the field relaxation effect.<
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