Abstract
Wet-design high voltage AC power cables are cost-effective alternatives to traditional lead-sheath cables, but the lack of a metallic water barrier can lead to water absorption in the cable insulation system. Intermittent load patterns can induce rapid cable temperature variations, which can induce supersaturation and then condensation of water during cooling at impurities in the insulation material. The main purpose of this paper is to study the effects of temperature cycling on water tree ageing in a homo-polymer high voltage AC XLPE insulation intended for wet-design cables. Rogowski test objects with 1 mm thick XLPE insulation were subjected to 3 or 10 kV/mm and 60 thermal cycles using a cooling rate of 1 °C/min. Sodium chloride particles were included at one of the semiconductor-insulation interfaces. The results show that the water trees appeared to be only affected by the level of applied electric stress when growing from the sodium chloride particles, suggesting that the level of applied electric field mainly affects water tree growth from very large ionic contaminants.