Measurements and modeling of water diffusion in water blocking tapes for high voltage extruded cables

The main objective of this paper is to characterise and numerically model the sorption of water vapour in three commercially available water blocking tapes for medium and high voltage extruded cables. The main purpose of these tapes is to avoid longitudinal water penetration. However, the swelling tapes can also delay radial water ingress in the cable, thus delaying the formation of water trees and extending the life time of the cable. Sorption measurements have been perfomed in temperature and humidity controlled climate chambers using ultra-microbalances at 22-80%RH and 30degC. The results show that the tapes have high sorption capability and that the equlibrium water vapour content do not follow Henry´s law. This is particularly clear at high water vapour pressures. The average diffusion coefficients increase by decades with increasing water vapour pressure indicating a strong dependence on water concentration.