Opening sequence optimization for La Coche pumps back-to-back start-up through electrically coupled Pelton unit.

Abstract

La Coche pumped storage power plant features 4 pump-turbine units and a Pelton unit, with the possibility for direct full frequency electrical coupling of the Pelton unit generator with the pump turbine motors. The back-to-back start-up mode consists in reaching synchronous speed of both pump unit and turbine unit by using the hydraulic power delivered to the turbine, without requiring absorbed electrical power peak usually perturbing the grid during pump start-up.The fastest start-up is achieved while the hydraulic power injected in the system is maximized. The associated risk lies in reaching levels of mechanical load of the Pelton runner that dramatically reduce the runner remaining lifetime at each start-up.The proposed work focus on the Pelton turbine nozzle opening law optimization to minimize the start-up time, while keeping the level of stress in the Pelton runner below a maximum allowed value. Numerical simulations coupling CFD and FEM were associated to train a surrogate model predicting the runner condition along the transient start-up sequence. Resolution of the first order differential equation of the coupled units start-up trajectory under boundary conditions defined from nozzle opening sequence allowed to assess both associated start-up time and stress levels.Results of the field measurement gathered during the commissioning phase were compared to simulation results to update the implemented model parameters and optimize the start-up sequence allowing fast and long lasting back-to-back start-up capacity.