6.6kV E-T方式CVケーブルの水トリー劣化の加速要因と絶縁破壊過程に関する研究

抄録

Some 6.6kV XLPE Power Cables are E-T type with the external semi-conductive layer wrapped with tape. In the E-T type cables, there have been many dielectric breakdown accidents due to water-tree degradation. The cables with dielectric breakdown were investigated. As a result, the unbridged water-tree was the cause of the breakdown. All of those cables were less than ten years old. In other words, the process of dielectric breakdown and the speed at which the water-tree develops were different from the knowledge of the water-tree. In the knowledge, first, the time to dielectric breakdown is at least 10 years due to the water-tree degradation. Second, the water-tree does not causes dielectric breakdown immediately even if it is bridged. Finally, the bridged water-tree causes dielectric breakdown due to the subsequent abnormal voltage. Therefore, in this study, the factors that accelerate the growth of the water-tree and the dielectric breakdown process were investigated. As a result, the acceleration factor was confirmed to be the ion products from the materials in the semi-conductive tape. Moreover, the dielectric breakdown process was considered through the shape of the water-tree and the aspect of the electrical-tree generated at the origin of the water-tree.