The shape analysis of the Phase Resolved Partial Discharge (PRPD) patterns is proposed here as a tool for acceptance test and quality control of individual, new bars and coils for ac rotating machines. An insulation system based on mica paper tapes can be considered in good conditions when the detected PRPD patterns address actually just to discharges occurring in distributed micro-voids, while patterns associated with other types of PD sources should be absent. By means of the suggested method, comparable results, in terms of identification of the discharge process, can be obtained testing different types of bars and coils, at different voltage levels and using different PD instruments and couplers. Experimental results that show the influence of the initial voltage conditioning period on both the PD amplitude and PRPD shape, are also reported and discussed.
