Design of XLPE cables and soundness confirmation methods to extra high voltage XLPE cables

The design of XLPE cables, degradation factors to working XLPE cables, and exclusion methods of the degradation factors are reviewed. In addition, the soundness confirmation methods of extra high voltage XLPE cables are reviewed. As degradation factors of XLPE cables, electric stress degradation, partial discharge degradation, and water treeing degradation exist. However, in XLPE cable design, water treeing degradation is not considered in particular. When initial soundness is confirmed in XLPE cables, long-term performance can be expected. Therefore, the process of excluding the initial defects in XLPE cable insulation, and checking the initial soundness of XLPE cables are emphasized during the development stage and in cable manufacturing. On the other hand, under immersed conditions, some degradation diagnoses are needed, although it is suggested that regular 66 kV cables have a lifetime of 30 years. The detection of the water treeing degradation signal is carried out at the present time. When the cables am intended for use until and beyond the lifetime limit of 30 years, it will be necessary to argue how to confirm the soundness of existing XLPE cables, including studying the degradation degree of the actual cables.