A6a: Hydro Generator Vibration Case Study

This presentation is a case study of troubleshooting elevated and unstable upper guide bearing vibration on a 120-MW Pelton hydro unit following a recent rotor major inspection.

Inconsistent responses during testing were observed based on the rate of change of turning speed during startup, bearing and stator temperatures, generator field excitation and therefore magnetic unbalance, as well as generator active and reactive power loading. A single plane field balance procedure was employed near the upper guide bearing to minimize turning speed frequency excitation forces at this location.

Additional testing was performed to confirm that vibration levels were successfully reduced to within acceptable limits for normal operating regimes allowing for unrestricted release to operations. However, this only addressed the symptoms and not the root cause which is believed to be related to early indications of fitment issues, either, the thrust block to shaft and/or of the generator rotor rim to spider due to aging.

Further investigation was performed on a sister unit which anecdotally seems to have a similar issue at an upcoming outage.