Study on water tree degradation diagnosis of XLPE cable using charge radar

Water tree is a significant degradation mode of power cables with polymeric insulation. The authors proposed a new diagnosing method for locating water tree degradation. In its procedure, a DC bias voltage is applied for poling the water trees, prior to applying a sharp probing pulse for depolarizing and locating the water trees. However, significant amount of cable lines are in connection with gas insulated stations (GIS). In such a case, applying DC voltage is to be avoided, since it may cause electrification on the insulation in the GIS, which may also induce a reduction in insulation performance. In this report, the period of time for bias voltage application was reduced into as less as 1.5 ms, which is equivalent to the duration of switching surge voltage. As the result response intensity was almost the same as that with 2 s in application time of bias voltage. In addition, theoretical study in terms of pulse response was performed.