On-line Measurements on Turbogenerators U

This paper discusses partial discharge (I%) measurcinciits performed on turbogcncrators us- ing the VMI: rn detection technique. With this tcchniquc it is possible to perform PD incasiirc- mcnts nn turbogenerators without interruption of Lhcir operation. In addition tu PD in any particular phase, the recorded patterns can show crosstalk froin other phases and disturbances. The nicinbership of each signalsource (phase's ow11 PD pattern, crosstalk, disturbances) to tlic rccordcd yattern depends ON thc selected center frequency, By cxainination of some typicaI ex- aiiiylcs, the relationship bctwccn the center frequency and recorded patterns is discussed, Fur- thermore, I'D tneasurcmcnts performed over tiinc 011 the same generator are stndicd to discuss possible changes in the spcctral responses of particular phases of B turbogenerator, By visital comparison of DO patterns as well as coinputer-based discrimination tools it was found that several ceirtcr frequencies aresuitablc in tune the VHF rD dctcction technique. However, these center frcqueocics cnii change in the COUTSC of time for a yarticiilar phasc of a turbogenerator. As a rcsult, in order to avoid a misjudgment on thc insulation condition of turbogenerators, thc analysis of on-line recorded PD should not be restricted to just one single center frcqucncy.