Rehabilitation of water tree aged XLPE cable insulation

The main purpose of this paper is to present results from rehabilitation experiments performed on laboratory aged Rogowski type test objects and samples of a 24 kV service aged XLPE cable. The results obtained show that impregnation with the rehabilitation liquids acetophenone and CableCure-silicone increased the AC breakdown strength of water tree aged test objects to a value higher than that of degassed and non-aged test objects. This high improvement seemed to be of permanent nature if the test objects were kept in direct contact with the rehabilitation liquid during the wet ageing following the rehabilitation. However, if the surplus rehabilitation liquid was removed water trees continued to grow and the improvement in AC breakdown strength was reduced to a value slightly higher than that of non-rehabilitated test objects. The examined XLPE cable was taken out of service due to long vented water trees initiated from the painted insulation screen. When keeping the CableCure-silicone liquid in direct contact with this insulation screen the average AC breakdown strength was found to increase by a factor of 2.1 after two months of impregnation at 20°C