The shape analysis of the Phase Resolved Partial Discharge (PRPD) patterns is proposed to assess the conditions of the insulation systems of ac rotating machines. By using this methods, it is possible to get consistent and comparable results even if tests are performed using different PD instruments or couplers. To be effective, this method requires a clear definition of the PRPD patters relevant to the different defect typologies that can affect the insulation system taking also into account the different insulation technologies. Due to the empiric approach, rules that allow to manage the uncertainty in the association patterns/defects, are also proposed. Some experimental results obtained testing off-line coils, bars and complete machines provided by different insulation systems, are discussed to show the validity of the method.
