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.