Characterization of Space Charge Distribution of Cross-Linked Polyethylene Cable Insulation Under Temperature Gradient Ageing

During the actual operation of high-voltage cables, there are differences in temperature between the center conductor and the outer surface of the cable, and the cross-linked polyethylene insulation of the cables has been in the temperature gradient ageing environment for a long time. Thus, it is particularly important to study the charge transport behavior of cross-linked polyethylene under the long-term ageing conditions of temperature gradient. In this paper, we designed a temperature gradient ageing device with adjustable temperature difference, conduct different temperature gradient ageing experiments for high-voltage cable slices. Meanwhile, we established a high-temperature ageing comparison ageing experiment. The space charge characteristics of crosslinked polyethylene (XLPE) slices aged for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7,14,21,35,42$</tex>, and 49 days at different high temperatures (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$40^{\circ} \mathrm{C}, 60^{\circ} \mathrm{C}, 80^{\circ} \mathrm{C}$</tex>, and 100° C) and different temperature gradients (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20^{\circ} \mathrm{C}, 40^{\circ} \mathrm{C}$</tex>, and 60° C) are measured by the space charge measurement equipment of the electroacoustic pulse (PEA) method. The measurement results show that compared with constant high-temperature ageing, the anisotropic charge of temperature-gradient-aged crosslinked polyethylene slices is more concentrated near the electrodes. Moreover, under the same aging temperature or temperature gradient, the amount of anisotropic space charge in the XLPE specimen increases initially and then decreases with the extension of aging time. Besides, the anisotropic space charge density peak exhibits a significant temporal delay in temperature-gradient-aged specimens compared to constant high-temperature aged counterparts.