Long term electrical properties of XLPE cable insulation system for subsea applications at very high temperatures

The main objective of this work was to examine the electrical properties of the XLPE insulation system subjected to very high temperatures in wet environments. The test program included thermo-electrical ageing of XLPE cable models. The ageing was carried out at temperatures up to 128 °C in both tap water and nitrogen atmosphere for up to 12 months. The results show that increasing the service temperature above 90 °C in wet environments can result in severe degradation of the XLPE insulation even at relatively low electric fields. However, no such degradation was observed during ageing in dry conditions with low concentrations of oxygen. Hence, an outer sheath system with a low permeability to water and oxygen should be applied at very high temperatures above 90 °C.