Determination of Surface Erosion Degree inside Dielectric Void Subjected to Partial Discharges

Abstract

Novel approach to determine degree of surface erosion inside void subjected to partial discharges is presented. The deterioration of the void wall is associated with a time decay of accumulated charges, which reflects changing surface conductivity. The introduced methodology is based on non-continuous, chopped partial discharges sequencing. It can allow to estimate post discharge charge decay in the void, calculated as a time constant of the decay of internal accumulated electric field from deposited charges. The chopped sequence consists of multiple series of packets containing the base waveforms, followed by the defined delay time between subsequent packets. Train of base waveforms is applied to a dielectric material and as a whole epoch repeated within given measurement time. Main focus is on the internal mechanism inside voids, especially with respect to void surface conditions and charge decay phenomena. The experiments were carried out in a gaseous voids in polyethylene filled with air at atmospheric pressure. Presented method reveals impact of deposited charges creating an internal field, which interplays with superimposed external electric field in terms of the discharge inception conditions. It was demonstrated that this methodology can reveal quantitatively charge dynamics based on partial discharges phase-resolved pattern and applied analytics. Time constant of deposited charge decay in void was estimated based on two measurements with different fill factors.

Parameters that influence the partial discharges occurrence in cavity defect within electrical cable insulation

“…-Significant variations in gaseous composition and pressure in cavity. -increase on the temperature in insulation defect [10,11,12].…”