Influence of wet ageing on the electrical breakdown strength of XLPE cable slices

In order to investigate the consequences of water-induced degradation on the dielectric breakdown field of polyethylene, the authors performed statistical electric breakdown strength measurements on cable slices previously aged in the presence of water. A Weibull analysis is performed on at least 40 sets of breakdown voltage data for each population, leading to a precise determination of the nominal breakdown field E₀. Comparison is made as a function of ageing time and testing conditions. Wet ageing under conditions of water tree development affects the breakdown strength of XLPE (cross-linked polyethylene) cable slices. The presence of water trees in the insulation must therefore be considered as potentially harmful