The effect of included flaws upon the AC breakdown of polyethylene

The effect of aluminum and HMWPE (high-molecular-weight polyethylene) gel particles on the AC breakdown strength of a cable-grade low-density polyethylene (LDPE) is quantified. Despite extreme care, it was found to be impossible to process ultraclean LDPE in small batches and maintain its electrical breakdown performance. Sufficient cleanliness was achieved for the LDPE to exhibit a measurable deterioration of performance upon the addition of aluminum particles in the range 38-53 μm but not in the range 15-38 μm. Above this size range a strong dependence of breakdown strength on particle size and defect concentration is reported. In material containing aluminum particles it has been suggested that two types of behavior can be discerned. One of these was attributed to individual particles and led to high-field failures. The second was attributed to their anomalous defects or to intentionally added defects acting cooperatively and caused low field failures. In the present study no clear trend in behavior was observed upon addition of gel particles. In some cases the control material was improved by the addition, a result that is tentatively attributed to changes in polymer morphology