In the paper a method is presented for the study of oscillatory problems of hydraulic generating units equipped with Francis turbines. The accurate equations of the turbine are implemented for the simulation, taking into account water hammer effect. Partial derivatives of turbine flow rate and torque with respect to head and gate opening are deduced from real measurements for the whole leading range. Speed governor dynamics are fully simulated, and the influence of torsional vibrations is studied. The vibration response of the unit to draft tube surges is investigated and the risk of excessive oscillations is evaluated. The approach was developed for diagnosis of excessive vibrations of Kastraki hydro power station in Greece.
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