Searching for Partial Discharge patterns for the identification of defects of insulation systems in ac rotating machines

Results of a comparative investigation having the purpose to select the most appropriate Partial Discharge (PD) pattern for robust identification of defect typologies in insulation systems of ac rotating machines, are reported in this paper. PD measurements were performed on some Roebel bars affected by specific defects. The Different PD-patterns were evaluated to verify their capability of identifying defects occurring in different setup conditions, different locations, or by varying voltage levels (robust identification). It was found that among the different PD patterns considered in this investigation, the Phase Resolved PD pattern exhibit features allowing the robust identification of a large number of defects types. The other patterns endured a high degree of ambiguity.