Thermal endurance evaluation of XLPE insulated cables

Abstract

Thermal endurance characterization of XLPE cable models is realized by applying conventional procedures and an analytical method. The latter method is based on oxidation induction time measurements to estimate the activation energy of the degradation reaction and then the slope of the thermal endurance line. The conventional life test at an intermediate temperature is used to determine the ordinate intercept of the same line. The estimates of temperature indices, obtained by different diagnostic properties and end-point selections on the basis of both conventional and analytical techniques, are fairly close, thus revealing the ability of appropriate analytical procedures to characterize reliably the thermal endurance of XLPE cables, with the advantage of shortening test times with respect to conventional methods. A discussion is presented on the choice of diagnostic properties and end points, in order to achieve thermal endurance lines and indices which provide actual information on cable performance under service stresses. Analysis of the possible choices is performed with reference to the results of multiple-stress tests which simulate service stresses and by investigating the aging mechanisms. Finally, considerations of the compensation effect applied to life lines, with reference to both Eyring and Arrhenius models, are made. Checks relevant to different property end points reveal very good agreement of the experimental results with the aging compensation effect.