Relationship between residual charge signals and AC breakdown voltages of removed 6.6 kV XLPE cables using residual charge detection method with pulse voltages

The residual charge method is a main diagnostic method for water tree degradation of cross-linked polyethylene (XLPE) cables in Japan. The authors have been developing a new method for diagnosis of water tree degradation of XLPE cables by using pulse voltages for charge accumulation and depolarization. In this study, we first applied pulse voltages with a pulse width of about 1 ms to removed 6.6 kV XLPE cables that had water tree degradation, and confirmed that residual charges were successfully detected in the removed cables. Then, we investigate the relationship between the residual charge signals and the AC breakdown voltages of the removed 6.6 kV XLPE cables. The results clarified that the removed cables with larger residual charge and longer duration of current signal related to water tree degradation had a lower AC breakdown voltage.