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Optimization of turbine start-up sequence of a full size frequency converter variable speed pump-turbine

Authors: J Schmid, S Alligné, D Biner, C Münch-Alligné, N Hugo and C Nicolet

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The stability of the electricity grid will be disrupted by the massive integration of new renewable energies. Hydropower plants have a major role to play in this transformation of the electricity market by increasing their operational flexibility and their ability to provide ancillary services. However, this flexibility may lead to an accelerated degradation of mechanical components. By changing the turbine operating point far from the best efficiency point or by increasing the number of transient manoeuvres such as start and stop sequences, unsteady flow phenomena, cavitation development and additional wear and tear stress the unit's components and impact its lifetime. The present work aims to provide preliminary insight on the optimization of the start-up sequence of a 5 MW reversible Francis pump-turbine equipped with a Full Size Frequency Converter (FSFC). The goal of the optimization approaches are to determine a start-up sequence which minimizes the runner damage, the penstock fatigue and the water losses. The objective functions are evaluated by 1D hydraulic transient simulations with the SIMSEN software and which it allow to compare the relative mitigation between the conventional fixed-speed start-up and the linear variable-speed start-up equipped with a Full Size Frequency Converter.

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