Time and Frequency Domain Measurement Methods for High Frequency Characterisation of Power Cables

University dissertation from Stockholm : Elektrotekniska system

Abstract: Time Domain Reflectometry (TDR) has been used forlocalisation of transmission line discontinuities in variousapplications. One of the challenges when applying TDR on powercables is to obtain knowledge of the high frequencycharacteristics of both the degraded and the undegradedsections of the cable. Two methods for extraction of the wavepropagation properties of power cables are developed in thisthesis. The first one uses TDR measurements and analyses theshort pulse propagation along the cable. It delivers thecomplex propagation con-stant in the frequency range 1 MHz -300 MHz. The second method is based on the S-parametermeasurements with a Network Analyser (NA). The method extractsthe complex propagation constant and the characteristicimpedance, as well as the LCRG Telegrapher's Equationparameters for the frequencies between 300 kHz and 300 MHz. Thedeveloped system and methods are then applied for diagnosticsof water de-gradedcable insulation. The first experiment usesTDR for localisation and parame-ter estimation of water ingressin mass-impregnated paper insulation. The second experimentutilises the S-parameters technique for high frequencycharacterisation of water-treed XLPE cable sample. Asensitivity check of the TDR system for measurements in thefield is also performed.

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