Partial Discharge Evaluation of Polyethylene Cable-Material by Phase Angle and Pulse Shape Analysis

This paper reports on the correlation of chemical and physical degradation as a result of discharge activity and partial discharge measurements, using only real quantities. The materials investigated are LDPE and peroxide crosslinked PE. An 8-channel test arrangement, controlled by a real-time microprocessor system, has been employed for time-critical evaluation and data organization. It was concluded that the lifetime of polymeric insulating materials depends on the type of internal partial discharges as well as on space charge and conductivity distribution. Two competing mechanisms make it difficult to evaluate discharge behavior near inception voltage: (1) Concentration of discharges to eroded surface areas causes an increase in deteriorating energy, and (2) Surface charges and electron trapping cause a decrease in the field strength. A scanning electron microscope was used to correlate electrical measurements to physical deterioration.