Mechanisms for degradation of TR-XLPE impulse strength during service aging

While the retained ac strength of TR-XLPE distribution cable appears to be quite good at about 80% of the ac strength of degassed, as-manufactured cable, the impulse strength appears to drop linearly over time and has been reported to drop by as much as 50% during the first two years of normal service aging before leveling off. In this paper, we discuss the mechanisms by which the impulse strength can degrade to a greater degree than the ac strength. Three frequency-dependent mechanisms, which include electrothermal, electromechanical, and electrical, have been identified.