The case of the vibrating generators
The case study in this article demonstrates that EASA members have great opportunities to develop and improve customer relationships by helping them solve their application problems. Several generators driven through gearboxes at a hydro site ran fine for years, until one excitor failed electrically. After being repaired and reinstalled, it performed well electrically but vibrated more than the other units. A few months later, a second generator experienced a bearing failure. The unit was repaired by the same service center, and it also vibrated after repair and reinstallation. By the time a third unit lost an excitor, the customer was looking for a different service center. Unfortunately, the results were the same. The customer pursued the issue. All told, four shops worked on these generators, but none improved the vibration. Finally, the first shop got another try. This time, a new technician examined the problems encountered and listened to those who were involved previously. Just as important, he looked at the application itself: the generators had welded rib frames, covered by sheet-metal shrouds. They were a two-bearing style, with an overhung excitor. The generator was then repaired and installed using the procedures outlined by the technician - and ran smoothly. What did the technician do to correct the problems?