Broadening the operating range of pump-turbine to deep-part load by runner optimization

To cooperate with new energy sources such as wind and solar, pumped storage units are required to frequently change conditions and operate under part loads, leading to the problem of violent pressure fluctuation and unit vibration. To meet this challenge, the next generation of pump-turbine runners will therefore have to be designed differently. The goal of this article is to construct a framework for broadening the operating range of pumpturbine to deep-part loads. In this study, a multi-objective optimization strategy for the runner with wider output range is suggested, wherein the blade control parameters, specifically the blade loading and blade lean angle, are optimized to enhance the efficiency, anti-cavitation, and stability of the pump-turbine runner. A runner with turbine output range of 40%-100% is optimized for a specific power station. Next, the impact of runner control parameters on runner performance is evaluated, and the runner geometric characteristics for different optimizing priorities such as the pump peak efficiency, cavitation performance, turbine rated efficiency, and turbine partial load efficiency, are concluded. The mutual restriction mechanism between the pump peak efficiency and cavitation performance of pump mode, as well as the turbine-rated efficiency and partial load efficiency of turbine mode, is revealed. The main contributions of this paper include putting forward an effective optimization design process for wide output pump-turbine, and pointing out the relationship between runner geometric characteristics and performance. The results indicate that the present approach can significantly improve the efficiency and stability of runners operating in deep-part loads. The blade loading pattern with hub section aft-loaded and shroud section fore-loaded, combined with negative blade lean angle, is recommended for such runners. Blades with a smaller wrap angle and lower arch are conducive to improving the pump peak efficiency and turbine-rated efficiency, while the opposite geometrical features are advantageous for improving the runner cavitation performance and efficiency performance under part load conditions. These findings can serve as an important guide for the development of runners with a wider output range.