A Study of the Pulse Propagation Behavior in a Large Turbo Generator

The experiment described in this paper was performed to gain a better understanding of the partial discharge (PD) pulse propagation behavior in the stator winding of a large turbo generator. The winding insulation was drilled at several locations in the slot section and in the end-winding area. A PD calibrator was used to inject artificial PD pulses at these locations. The pulses were then measured at different sites, including at the line terminal, using both a frequency-selective PD measurement system and a wideband digital oscilloscope. The results are displayed using an attenuation matrix where a normalized measured quantity is plotted as a function of distance from the sensor. Several different frequency bandwidths were used to demonstrate the advantages of the apparent charge measurement in the low frequency range. Two main pulse propagation modes are discussed in this paper: a) a slow mode and b) a fast mode. Different examples are used to show the effects of pulse attenuation and cross-coupling between bars in the end-winding area. In addition, some common industry practices related to PD measurement on stator windings are briefly discussed.