Analysis of the Vibration Characteristics of Pumped-Storage Units During Load Shedding in Power-Priority Mode

Variable-speed pumped storage units perform flexible and rapid regulation tasks in power grids. However, under the “power-priority” control mode, the superposition of maximum energy operating point and extreme transient events such as load rejection can induce severe vibrations. This study investigates the vibration characteristics of a variable-speed unit under a typical extreme condition (Case RT-5): power-priority mode, maximum energy superposition point, and load rejection at extreme rotational speed. A one-way fluid–structure interaction (FSI) numerical method is employed, combining unsteady Reynolds-averaged Navier–Stokes (URANS) with a shear stress transport (SST) k-ω turbulence model and finite element structural analysis. The innovation lies in quantitatively linking the transient hydraulic excitation (water hammer pressure waves, non-stationary pulsation field) to the mechanical response (centrifugal force, variable stiffness) to identify the root causes of vibration. Results show that under RT-5, the maximum equivalent stress reaches 97.09 MPa and maximum deformation 0.66 mm, occurring at the blade-crown connection root—a stress concentration zone. However, below the material yield strength (265 MPa), the stress rises 2.4-fold within 12 s, and secondary stress peaks appear, indicating high-cycle fatigue risk. Severe fluctuations of stress and displacement, driven by coupled hydraulic-mechanical excitation, are the main causes of vibration. This study provides a theoretical basis for safety assessment and control strategy optimization, and proposes that RT-5 be included as a mandatory verification case for variable-speed units.