The deterioration diagnosis for XLPE cables using low-frequency voltage has been confirmed that it is able to detect not only bridged water trees but also un-bridged water trees. However, its degraded detecting performance has not been proven.
In this paper, we examined the properties of a DC leakage current and a low-frequency loss current through the use of cables with different degrees of deterioration, and studied the performance of each measurement in detecting water-tree deterioration.
As a result, it has been confirmed that for a water tree that has bridged an insulator, it is possible to detect deterioration in both the DC leakage-current measurement and the low-frequency loss-current measurement. On the other hand, for a water tree that has not bridged an insulator, although deterioration signals were not obtained in the DC leakage-current measurement, as is generally known, it has been ascertained that deterioration can be detected in the low-frequency loss current measurement.
The above results has made it clear that the result obtained by the method of combining low-frequency method with DC leakage current method is high reliability.