Two Kinds of Whirl on Fixed-Blade Propeller Type Turbine

Two kinds of whirl have been identified on propeller-type generating units. In both kinds, the shaft whirl follows the same direction as the rotation of the machine and the source of the instability seems to be the interaction between the fluid and the structure. The first kind of whirl was observed at 0.33 Hz at plant #3 of Hydro-Québec’s Beauharnois powerhouse and, also, at 0.25 Hz at LG-1 and Carillon. It occurred below the peak efficiency operating range. The vibration at 0.33 Hz (0.21 times the rotation speed) affects not only the power output but also the vibration at the guide bearing and the pressure in the penstocks. The second kind of whirl was observed at around 5.14 Hz (3.6 times the rotation speed) at LG-1 and occurred at no load or low load. Measurements at the bearings combined with those of the runner displacements reveal that the shaft undergoes like the second bending mode. Proximity and pressure measurements taken where the blade passes on the discharge ring of the runner at LG-1 shows that the whirl at 5.14 Hz is due to a runner instability.