Characteristics of PD pulses in electrical trees and interfaces in extruded cables

The characteristics of partial discharge (PD) occurring within electrical trees in extruded cable insulation, and also at model interfaces between a cable and its accessories, have been investigated. A wideband PD detection system was used that enabled the true shape of the PD pulses to be measured. The rise- and fall-times, pulse width, amplitude and frequency of the pulses were recorded as electrical trees grew through the insulation, and also as the tracking progressed along a model cable/accessory interface. The PD pulse characteristics in electrical trees varied with time of voltage application and also with the electrical stress in the insulation. Differences in the PD characteristics of electrical trees in the bulk of a polymer and at interfaces between polymers were observed.