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The sequence of the protection components of a hydraulic power plant during normal, exceptional or accidental events plays a fundamental role for the safety of the installation. The operating times of these components are a key parameter in the safety chain. The penstock protection valve is aiming to cut off the discharge in case of pipe burst and closing time will depend on the forces balance on the valve obturator.

The Montbovon hydroelectric power plant located in Canton Fribourg in Switzerland, which is operated by Groupe E SA, comprises an upper reservoir, a headrace tunnel, a headrace surge tank, two penstocks and two Francis turbines generating units of 16 MW each, operated under a maximal gross head of 90 mWC. In the framework of the review of the safety chain of the Montbovon power plant, a dynamic model of the butterfly penstock protection valve has been developed for hydraulic transient simulations of pipe burst. This model is based on the momentum equation which takes into account the different torques acting on the obturator. Consequently, the valve closing time results from the simulation and is not imposed a priori into the simulation. Similar model was developed to simulate unit valve closing for normal scenario such as emergency shutdown or quick shutdown [1]. The model developed in this paper goes further by taking into account the cavitation influence which occurs in case of pipe burst. First, the dynamic penstock protection valve model is presented. Then, measurements of closing valve with water discharge at different output power of the unit are used to calibrate and validate the developed valve model. Finally, simulation of pipe burst is performed with different modelling approach of the system which highlights the influence of cavitation modelling.

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