Degradation rates in high voltage subsea cables with polymeric water barrier designs

This paper presents results from numerical calculations of water ingress in a wet designed subsea XLPE cable equipped with a two-layered outer sheath, and results from water tree ageing at different relative humidity (RH) levels in an XLPE cable core. The results from the water tree ageing show that no trees appear at RH below 70 %. Low water tree density and lengths were found at RH values between 70 and 100 %. This indicates that the service lifetime can be very long for cable systems with two-layered sheaths, as it takes more than 50 years to reach 70% RH and then additional 100 years to increase the RH from 70 to 99 % in the cable insulation.