Evaluation of Charge Absorption Ratio by Space Charge Measurement and Current Integration for Artificial Degradation Cables Including Impurities

This paper proposes a new insulation diagnostic index, referred to as the charge absorption ratio, defined as the ratio of the absorbed charge to the integrated external current. Simultaneous measurements of space charge distribution and external current were performed on 6.6-kV XLPE cables. Artificial degradation was introduced by doping into the insulation layer with olive oil containing oleic acid, which acts as charge hopping sites. The results demonstrate that the charge absorption ratio decreases with increasing voltage application time as well as with increasing degree of degradation. For non-doped cables, the charge absorption ratio remained above 0.8 during the first several minutes after voltage application, indicating that the dominant current component in this period is the absorption current. In contrast, doped cables exhibited a rapid decrease in the charge absorption ratio, reaching approximately 0.2 within a few minutes. These results indicate that the charge absorption ratio sensitively reflects changes in the balance between absorption and conduction currents caused by insulation degradation. Therefore, the proposed index is considered to be an effective parameter for evaluating the degradation state of power cable insulation.