Estimation of medium voltage cable parameters for PD-detection

Medium voltage cable characteristics have been determined with respect to the parameters having influence on the evaluation of results from PD-measurements on paper/oil and XLPE-cables. In particular, parameters essential for discharge quantification and location are measured. In order to relate a measured signal at the cable terminations to a specific PD-amplitude and location on the cable, the attenuation and the transmission speed of PD-pulses on the cable have to be known. Consequently, the main parameter to be determined is the complex propagation constant which consists of the attenuation and phase constants. A method to estimate this propagation constant, based on high frequency measurements, is presented and is applied to different cable types under different conditions. The influence of temperature and test voltage is investigated. The relevance of the results for cable diagnostics is discussed.