The paper presents a detailed numerical model of the dynamics of a Pelton turbine installed in a hydroelectric plant. The model considers in detail the Pelton turbine with all the electromechanical subsystems, such as the main speed governor, the controller and the servoactuator of the turbine nozzle, and the electric generator. In particular it reproduces the effects of pipe elasticity in the penstock, the water inertia and the water compressibility on the turbine behaviour. The dynamics of the surge tank on low frequency pressure waves is also modeled together with the main governor speed loop and the position controllers of the nozzle needle actuators and of the hydraulic electrovalve. Model validation has been made by means of experimental data acquired during some starting tests after a partial revamping of a hydroelectric unit, which involved also the control system of the hydraulic actuators but not the nozzles. The model is used in order to identify the cause of the oscillations of the electric power mainly ascribed to the backlash of the nozzle needle system.

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