Risk of penstock fatigue in pumped-storage power plants operating with variable speed in pumping mode

The upgrade of a pumped-storage power plant (PSPP) to allow variable speed operation offer severaladvantages in pumping and generating modes. However, in pumping mode at part load, both pressureand torque pulsations develop in the pump turbine runner. This paper evaluates the risk of fatiguedamage in the penstock of a variable-speed PSPP due to the propagation of the pressure pulsationsdeveloping in the pump turbine runner at partial load in pumping mode. For that purpose, a simulationmodel of a variable-speed PSPP has been developed. The pressure and torque pulsations are generatedeach from a different set of sinusoidal functions calibrated from the results of a Computational FluidDynamic model, which was in turn validated from experimental data. A Monte Carlo simulation has beenperformed considering different temporal gaps between the sinusoidal functions reproducing thepressure pulsations in one and another pump turbine. The number of stress cycles that may cause fatiguedamage in the penstock has been obtained from the results of the simulations and the fatigue curvesdefined in the Eurocode, and then transformed into the maximum number of hours per year the PSPPcan operate at partial load in pumping mode to avoid fatigue damages.