Numerical Prediction Study on Dynamic Characteristics of Key Components of a Variable-Speed Hydro-Generator Unit Under Load Rejection Conditions

To evaluate the structural safety of variable-speed pumped-storage units under extreme transient conditions, this paper focuses on a variable-speed unit at a specific pumped-storage power plant. Based on boundary conditions measured during on-site load shedding tests, a three-dimensional, unidirectional fluid–structure interaction numerical model was established, incorporating stationary components such as the volute, base ring, top cover, and bottom ring. A numerical prediction and analysis of the dynamic stresses and deformations of key components were conducted for a hazardous scenario in which all units shed load simultaneously and the volute pressure reached its peak. The results show that during the load shedding process, the maximum static stress in the stationary components was 79.5 MPa, and the maximum displacement was 0.066 mm; both occurred 46.01 s after load shedding at the junction between the guide vane outlet edge and the top cover, and this value is far below the material’s yield strength of 490 MPa. Preliminary numerical evaluations indicate that the unit’s stationary components meet strength design requirements under this extreme transient condition. Furthermore, the study revealed the time lag mechanism between the peak hydraulic load and the peak structural stress in the top cover. The numerical prediction method established in this study can provide technical support for the structural safety assessment of transient processes in variable-speed units.