High frequency characterisation of water-treed XLPE cables

Time Domain Reflectometry (TDR) has been used for localisation of transmission line discontinuities in various applications. One of the challenges when applying TDR is to obtain knowledge of the high frequency characteristics of both the degraded and the undegraded sections of the cable. The wave propagation characteristics of water-treed XLPE cables are investigated in this study. The parameters are extracted from the cable S-parameters measured with a Network Analyzer (NA) in the frequency range from 300 kHz to 300 MHz. The cable samples are characterised at different temperatures and with different water content of the water trees. The effect of the application of nominal voltage for extended period on the cable wave propagation characteristics is also shown. High voltage dielectric spectroscopy is used as a reference method for estimation of the level of water tree deterioration.