Results on after-laying test of 275 kV XLPE cable line

In 2002, Chubu Electric Power Co., Inc. (CEPCO) completed a 275 kV underground transmission line called the Kawagoe-Nishinagoya Line between Kawagoe Thermal Power Station and Nishi-Nagoya Substation, and conducted power-frequency withstand voltage tests on the line. Based on the characteristics of partial discharge that has been found at various defects in recent years, the tests were separately conducted in respect of each phase under the following test conditions: the withstand voltage test value was set at 207 kV, which is 1.3 times as high as the operation voltage to ground, and the time of application of voltage was set at 20 hours. As a result of the tests, partial discharge was found in one phase of the 2-circuit 6-phase line about five hours after the start of application of voltage. Of the foil electrode sensors installed at several points, the time difference between the start of application of voltage and the occurrence of partial discharge was measured by sensors at two points for position location, and the partial discharge was located in the immediate neighborhood of the joint. The part in question was removed and repaired, and voltage was applied again to the part, and we confirmed that there was no problem on the line and after-laying test was effective in detection for the defects of 275 kV XLPE cable. The removed part was carried to our factory and investigated in detail. As a result, a peel as thin as about 0.1 mm was found between the outer semiconducting layer of the cable and the insulator.