On the lack of correlation between PD readings and failure location in high-voltage stator bars

After showing in a previous work that PD measurements suffer from poor repeatability and reproducibility, the present study turns now to a more qualitative approach, investigating if a method of PD fault location along a Roebel bar length can be used to identify insulation critical areas that later on could fail under electrical stress. Typical insulation “damages” have been created on the components in advance by submitting them to both thermal-mechanical and electrical aging tests. Once such preliminary aging was done, the critical areas along the bars length were identified by mapping the PD readings on each component. Afterwards, every bar was subjected to a destructive electrical breakdown test. At last, the breakdown locations were compared with the PD mappings to search for any possible correlation between the two events. Based upon the present results, such correlation does not exist.