Partial discharge characteristics till-breakdown for XLPE cable joint with an artificial defect

Insulation degradation mechanism and identification of defect types for cross-linked polyethylene (XLPE) cable and joint have not been cleared yet. Measurement of partial discharge (PD) is one of the most important things of testing the high voltage cable. In this paper, we investigated PD characteristics measured for practical XLPE cable joint by the so-called foil electrode method, in which aluminum foils are rapped onto the cable sheath at insulated cable joint to form coupling capacitance. We measured aging time dependence of phi-q-n patterns and PD statistic parameters when an artificial defect (a needle void) was placed in XLPE/EPR (ethylene-propylene rubber) interface. As a result, phase-resolved PD patterns (i.e., phi-q-n patterns) were found to depend upon the defect type varying with aging time. Moreover, we investigated mechanism of degradation process leading to breakdown by comparing experimental results of XLPE cable joint and simulated XLPE cable joint (model sample).