Evaluation of the fatigue-related influence of start-ups on Pelton turbines based on reduced scale model stress measurements

Abstract In recent decades, the electricity industry has undergone a significant transformation from a vertically integrated supply system to a market-regulated structure. This shift, along with the intermittent nature of increasingly prevalent non-dispatchable renewable energy sources, induces system operators to redistribute portions of the power generation included in the market schedule to preserve the energy balance within the power system. For hydropower plants, this translates in increasingly frequent operations in transient condition, with significant fatigue-related consequences on the lifetime of hydraulic machines. The understanding of fatigue phenomena during transient operations requires therefore experimental investigations, modeling and optimization of such operations, representing today a relevant research subject. This paper proposes the comparison between two methodologies which aim to estimate and optimize the operational cost, with respect to the lifetime of a Pelton turbine, of the specific case of the back-to-back start-up of a multistage pump performed with the Pelton runner of the same ternary group. These methodologies are developed on data collected during an experimental campaign performed with the reduced scale model of the investigated turbine, homologous to the real test case pumped-storage power plant. Despite the substantial distinction in the adopted approaches, the two methodologies show common features in terms of the fatigue damage trend as a function of the turbine operating conditions, and of the optimal strategy minimizing the structural impact of start-up sequences.