Water Tree Growth in XLPE Polymeric Insulation Induced by Various Types of Defects

Paper in proceeding, 2025

Water treeing is a critical degradation mechanism in polymeric insulation of high voltage cables. It reduces the electrical performance of the insulation thus resulting in shortening cable lifetime. Various defects such as micro-voids, mechanical damages, structural irregularities all leading to a concentration of electrical stress, can initiate and accelerate the water tree (WT) growth. In this work, changes in the structure and appearance of WTs in cross-linked polyethylene insulation induced by various types of defects are investigated. Artificial defects created with the help of a heated needle and sandpaper were introduced on flat samples of XLPE material, which were further immersed in salt water and exposed to high test voltages. The size and morphology of the obtained WTs were analyzed using optical microscopy and quantitative measurements were performed to evaluate tree length, branching density, and growth rate based on their defect-induced growth characteristics. The observed tree patterns correlate well with the types of mechanical damage produced by different types of defects. The results contribute to understanding of water tree initiation and growth mechanisms in polymeric cables.