The Influence of Strain on Water Treeing in XLPE Power Cables

By bending commercially available XLPE power cables around hollow cylinders with different diameters, the insulation was subjected to a wide range of tensile and compressive strains. By using a simplified model, the applied compressive and tensile axial strains at the conductor screen of the bent cables were estimated to be in the range of 0-18 %. Both the density and growth of vented water trees at the conductor screen increased significantly with increasing applied axial tensile strain, and a corresponding reduction was observed for compressive strain. Approximately 98 % of the vented trees grew from the conductor screen, probably caused by higher electrical field stress and exposure to lower temperatures during the manufacturing process. The angular distribution of bow-tie trees was similar to the distribution of vented trees.