Evaluation of relationship between residual charge signal and AC breakdown strength of removed XLPE cables at 22, 66 and 77 kV classes by detecting residual charge due to water tree degradation with pulse voltages

摘要

The authors have been developing a new diagnostic method with pulse voltages instead of the DC and AC voltages in the conventional residual charge method. In this study, we applied pulse voltages with the pulse width of about 5 ms to removed XLPE cables at 22, 66 and 77 kV classes, and we succeeded to detect current signals related to water tree degradation. Then, we investigated the relationship between the residual charge signal and the AC breakdown strength of the removed cables. As a result, it was found that the ratio of the duration of the current signal related to water tree degradation to the rise time of the applied pulse voltage had strong correlation with the AC breakdown strength, and it can be a water tree degradation index.