Estimation of Water Content in Cross-Linked Polyethylene Insulated Cables by Fourier Transform Infrared Spectroscopy

Abstract

Water has deterimental effects on electrical properties of polymeric insulation, such as increasing dielectric losses and reducing short-term and long-term breakdown voltage. In polyethylene (PE) insulated power cables the combined action of the ac electric field and the conducting water produces localized degradation which has a tree-like structure (a few microns in size) called water treeing. Water is introduced into the insulation either by the manufacturing process or during handling, installation, and operation. In steam-cured cross-linked PE(XLPE) cables, water condenses in the form of microscopic cavities or clusters in amounts exceeding its solubility limit in PE, giving rise to the presence of a "halo." A knowledge of total water content and its interaction with PE matrix is therefore of prime importance for the understanding of the performance of the cable insulation.