DC Electrical Trees in Polymer Insulation Inflicted by Rapidly Decreasing Short Circuit Voltage Flanks

Paper i proceeding, 2022

This work aims to study the appearance and changes in the partial discharge pattern due to electrical treeing degradation of XLPE, a copolymer blend, crosslinked through a byproduct-free curing reaction, and LDPE when exposed to a series of high voltage short circuits. A wire-plane type test object has been employed and the presence of electrical trees were detected visually and by measuring the partial discharge (PD) activity. It was observed that PD characteristics changed with increased number of short circuit events. In particular, both the summed amount of PD magnitudes as well as the number of PDs increased due to the growth of electrical trees. These results were in good agreement with the hypothesis of electromechanical stresses analogue to mechanical crack formation which increase the volume of the defects thus affecting the PD characteristics. Additionally, clear differences in the phase distribution of PDs were observed that allows to use them as indicators of material performance and as complement to DC conductivity measurements and frequency domain spectroscopy.