Modelling and Practical Analysis of the Transient Overspeed Effect of Small Francis Turbines

The transient overspeed effect of slow Francis turbine can be a major factor in the design of a small hydroelectric scheme with long penstocks or tunnels.After a full-load rejection, iit a small hydroelectric power plant equipped with low inertia Francis turbine, the runner speed will increase and the runaway conditions can be quickly attained. The hydrotransients induced by overspeed of reaction turbines depends on the turbine type. The specific speed indicates the main characterization of the turbine behaviour in what concerns the flow variation during runaway conditions.In order to improve the pressure transient analysis since the early phases of the design of the hydraulic circuit, for lack of information about the equipment to be installed, the authors present in this paper a simplified method for reaction turbines modelling that was validated by computational and experimental comparisons.