Hydrodynamic simulation and investigation on the pumping reliability of a mixed pumped-storage power station

Mixed Pumped-Storage Power Stations (MPSPSs), transformed from cascade hydropower systems, are critical to improving grid flexibility amid increasing renewable energy penetration. However, during pumping operations, a hydrodynamic issue known as the pumping funnel, characterized by a rapid water level drop near the inlet or outlet, can severely impact system reliability. This study establishes dual hydrodynamic models (MIKE 21 and HEC-RAS) to analyze this phenomenon in the Lianghekou MPSPS (1200 MW total capacity), currently the largest MPSPS under construction in China. This study has developed a dual-index framework combining flow deviation and funnel hydrodynamics to evaluate pumping reliability. A pumping limit point based on a 5% flow deviation threshold, with baseline continuous pumping duration limited to 6.8 h, has been identified; and multi-scenario simulations have been applied to quantify the effects of inlet/outlet layout, conveyance capacity, and operational flow conditions. Notably, optimized layout and conveyance capacity improve pumping duration by 0.64 and 2.24 h, respectively. Qualitative analysis reveals that pumping reliability is sensitive to hydraulic design and boundary flow conditions and that proper engineering interventions can mitigate funnel formation. This work provides simulation-based evaluation methods and actionable guidance for the design and operation of large-scale MPSPSs in complex river basins.