Relating laboratory testing to service ageing of XLPE and EPR insulation in 11 kV distribution cables subject to water ingress

Laboratory ageing has been compared with seven years service for the same XLPE and EPR insulated 11 kV cables. The two different EPR compounds from service have retained higher breakdown strengths than the XLPE insulation. Most of the cables have solid conductors and an isothermal ageing test has been used. Recently manufactured XLPE cables have been compared with older cables during ageing in water. The two EPR compounds taken from service have been compared with other EPR compounds using a range of analytical methods. The one distinguishing feature is the high water absorption of the two compounds used in service. A different approach to life prediction for cables containing water trees is introduced, and the manner in which a water tree causes breakdown is related to the field enhancement of the water tree