Dissipation factor and water treeing of WTR-XLPE cable insulation

Tests three commercially available water tree retardant XLPE materials (WTR) and compares some of their properties with conventional XLPE insulation. The authors have focused on water treeing and dissipation factor. Water tree tests have been performed on Rogowski type test objects at room temperature ( approximately 20 degrees C), energized by an AC stress of approximately 10 kV/mm, for up to nine weeks of ageing ( approximately 1500 hours). This paper shows that water trees are initiated also in WTR-materials and their growth rates are approximately as for conventional XLPE. It is also shown that mechanical strain eases both initiation and growth of water trees. In particular one of the WTR-materials was significantly more affected than the other materials.