Elimination of upper bracket resonance in extremely high head Francis hydro-generators

Resonance occurred in the upper bracket of extremely high head Francis hydro-generators due to rotational vibrations. The vibration source was determined from field tests and a finite element analysis (FEA) of the structure. The first order natural frequency of the integrated structure including the upper bracket and the stator frame was then altered using the FEA model. The resonance during overspeed operation was eliminated, with the results verified by field tests.