Use of spectral analysis and phase resolved partial dischargemeasurements for generator testing

摘要

A water cooled 291.5 MVA steam turbine generator was monitoredonline for partial discharge activity by means of electromagneticinterference measurements (EMI). The results presented an increase ofactivity by a factor of 10 in the frequency ranges 10 to 60 kHz and 30to 50 MHz over 7 months of operation. After this period the generatorwas taken out of service for a planned stator rewind. Off-linemeasurements were then carried out on the three individual phases, bothfrom the neutral and line end of the phase windings. For comparison withEMI measurements a combination of spectral analysis and phase resolvedpartial discharge analysis (PRPDA) was used for the off-line tests inthe frequency range of 100 kHz to 100 MHz. In the low frequency range,activity could be observed on all phases whereas high frequencydischarges in the range of 50 MHz to 100 MHz were only present on phase1. Moreover, it was determined by the off-line spectral analysis thatthe discharge source was in the end arm region on the line side of phase1. The PRPDA results added one dimension to this information, revealingthat the high frequency discharge pattern was asymmetrical with regardto the applied 50 Hz with rated line-to-ground voltage applied. At theend of these tests each phase was subjected to overpotential testing