Analysis of a numerical model for the oscillatory properties of a Francis turbine group

The present work represents an assessment of the authors' several years of study on the application of the transfer matrix method to hydropower plant components. It is part of the strong research effort promoted by ENEL-DSR-CRIS on the oscillatory properties of hydropower groups equipped with Francis turbines, particularly important in presence of cavitating vortex rope (CVR). The paper concerns the study and the implementation in a computer code of a model for a group composed by a Francis turbine, an alternator and a speed governor. The model has been developed by the same authors [1] and its final result is the determination of the turbine hydraulic impedance. The fundamental characteristic is maximum generality and rigourousness at the same time so that most of the possible interactions with speed governor and alternator (a priori not neglectable) may be taken into account. This kind of approach has been imposed by the lack of knowledge about the problem and has led to a rather complex model whose simplification will be the next step of the work.