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.
S. Haridoss, R. Tobazéon, and J.-P. Crine, "Estimation of Water Content in Cross-Linked Polyethylene Insulated Cables by Fourier Transform Infrared Spectroscopy," Appl. Spectrosc. 42, 186-188 (1988)