Development of pre-breakdown discharge detection test for aged XLPE cable to find a deteriorating water tree

XLPE cables have been widely used in power transmission and distribution system especially in urban areas, since about 40 years ago. Nowadays, some XLPE cables have been operated for about 30 years, which is designed lifetime in their production. Therefore, understanding voltage withstand stress of aged XLPE cable is important for reliable operation and optimized replacement planning for the aged XLPE cable. CRIEPI has been investigating ac voltage withstand level and the degradation cause for aged XLPE cables that are removed from actual power grid due to replacement. This paper introduces the outline of the pre-breakdown discharge detection test system and some development of testing technique, and a characteristic result.