Diagnostic techniques that can determine the operating state of a power apparatus are essential for detecting the extent of degradation caused by aging during service. Such techniques could predict the remaining life of the apparatus and also reduce unscheduled outages, improve maintenance planning and increase system reliability. The life of a high voltage apparatus usually depends on the operating state of its electrical insulation. Analysis of the fundamental dielectric processes has shown that the polarization phenomena are strongly influenced by the morphology and degradation of the polymeric insulation. The Polarization/Depolarization Current Response is a non-destructive method that determines the depolarization current after poling the insulation with dc voltage. This technique is commercially available to detect the operating state of polar dielectrics such as transformer oils and oil/paper insulation systems [1,2,3] and complicated analyses of the depolarization current for cable insulation have also been reported [4,5]. However, the technique has been less successful for polymeric insulation of underground cables because the dielectric relaxation signals are much weaker due to the non-polar nature of such materials. This paper describes the polarization and depolarization current responses from XLPE cable insulation with and without water trees. Comparison of the polarization current with the time of polymer aging suggests that the analysis of the polarization current alone could be used to determine the operating state of the insulation. The advantage of this approach is that the polarization current provides consistent results and eliminates the need to acquire and analyze the depolarization currents as a function of the poling time.
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