Service aged 69 and 115 kV XLPE cables

Five 69 kV XLPE cables, 6 to 23 years in service and two old vintage cables from storage plus a 115 kV XLPE cable from service together with a spare cable from the same production, kept in storage, were evaluated. All components of the cables were found to show little signs of deterioration except for AC breakdown. The 69 kV XLPE cable from service has breakdown levels ranging from 10.2 to 18.2 kV/mm, the spare cable 15.0 to 17.7 kV/mm compared to 27.2 kV/mm, the only previously reported value for a new cable. The 115 kV XLPE cable had a breakdown level of 16 kV/mm and the spare 10 kV/mm. The above cables are low-stress cables. Most modern cables operate at higher voltage stresses, taking advantage of cleaner insulations with smoother shields and moisture barriers. Caution is advised in using older, low-stress cables placed in storage