By means of permanently installed 80 pF capacitive couplers, Manitoba Hydro has been making semiannual on-line partial discharge analyzer measurements on air cooled hydro generators and on various hydrogen cooled machines for periods as long as 20 years. Recent RCM initiatives require that the need for off-line tests and inspections be reviewed and justified with on-line monitoring to be used for trending wherever possible. This paper discusses the extent to which the on-line PD measurements have responded to deterioration that has developed in these windings over the 20 year period of time as verified by off-line tests, inspections and in-service failures.
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