Dielectric spectroscopy of XLPE cable insulation: comparison between time-domain and frequency-domain methods

Dielectric relaxation measurements were conducted on XLPE (cross-linked polyethylene) insulation samples extracted at different radial positions from laboratory-aged (24 kV/mm) cables in order to determine if they were an appropriate diagnostic for detecting change in the dielectric properties of cable insulation aged under high electric stress. Time-domain and frequency-domain spectroscopy measurements were performed on the same samples in order to evaluate the reliability of these methods. The dielectric parameters show a marked dispersion with the radial position of the samples from the inner to the outer semiconductors. The slightly, but systematically, higher average loss tangents found for the aged samples were within the dispersion. Hence, at this time, no evident correlation with electrical ageing can be inferred, and more detailed studies, as well as more intense ageing, are needed for definitive conclusions