Katsumi Uchida, Yoichi Kato, Masahiko Nakade, Daisuke Inoue, Hiroyuki Sakakibara, Hideo Tanaka
The authors have developed a method that uses very low frequency (VLF) voltages to estimate the remaining life of lines using 22- to 77-kV XLPE cables that have undergone water-tree degradation. VLF testing has been considered the most effective form of voltage withstand testing from the standpoints of the size of the test equipment, water-tree detection capability, and test soundness. Breakdown tests were carried out on field-aged cables and model cables, and the relationship between water-tree degradation and breakdown level was investigated. A database of the results was subjected to statistical analysis, and a novel method is proposed for determining a test voltage that makes it possible to estimate the remaining life of 22- to 77-kV XLPE cables; a suitable test voltage was determined. Based on these results, prototype field test equipment was built, on-site tests were carried out, and satisfactory results were obtained.