Publication
Grid regulation capacities of Pumped Storage Hydropower Plants (PSHPs) are of great importance for today’s and future power supply systems. In this context, variable speed technologies provide solutions for enhanced operational flexibility of PSHP units. Especially for turbine operation with variable head and part load conditions, the adaptation of the rotational speed offers benefits in terms of hydraulic efficiency, mitigation of pressure fluctuations and accordingly the fatigue behavior of hydromechanical components. The present work deals with numerical assessments of the pressure fluctuations on the runner of a 5 MW reversible Francis pump-turbine prototype equipped with a Full Size Frequency Converter (FSFC). The study aims to asses the impact of head and rotational speed on the pressure fluctuations at different load levels. Three power levels with a speed variation of ± 12% are investigated by single phase unsteady CFD simulations considering two different net head values with a variation of 20%. The numerical results give some insights on the scalability of the pressure fluctuations on the runner at the different operating conditions. It is demonstrated that rotor-stator interaction (RSI) related fluctuations are well scalable. Important transposition errors are found for low frequency fluctuations and stochastic content which is partially explainable by the limited statistical information provided by the numerical results. Finally it is shown that important mitigation of the pressure fluctuations can be achieved at deep part load conditions thanks to variable speed.