Water Trees as a Dominant Deterioration Cause of 60 kV Class Dry Cured XLPE Cables

The XLPE power cable has been widely used in power transmission and distribution system since middle 1960's, and many of them in 60 kV class grid under present operation was laid till mid 1980's to the end of 1990's. Their age is reaching their designed lifetime of 30 years or exceeding it, and the grid system operators require information of electrical insulation capability of their XLPE cables. This paper firstly reveals the insulation capability of such aged 60 kV class XLPE cable by the pre-breakdown discharge detection testing techniques. Then, it is clarified that the water tree is dominant degradation cause of such XLPE cables even manufactured by dry-cured and three-layer simultaneously extruded processes, which are considered to avoid water tree generation and development.