Three-dimensional simulations of load rejection processes of a variable-speed pump-turbine under different initial rotational speeds

Abstract

Abstract The load rejection transient process is one of the most dangerous operating conditions in pumped storage power stations. When the operating point slides through the S-shaped region quickly, the pressure fluctuations increase sharply and the unit vibrates obviously. In variable-speed units, the different initial rotational speeds have significant effects on the operating point trajectories during load rejection processes. In this paper, under the same head and guide vane opening, the load rejection processes with different initial rotational speeds were simulated by using three-dimensional methods, and the variations of rotational speed, discharge and torque were obtained and analyzed. The results show that the changes of initial rotational speeds affect the shapes of velocity triangle at the runner inlet and outlet, and causes the flow separations and vortices in the runner and draft tube, which leads to different efficiency and torque of the pump-turbine under initial steady conditions. In addition, during load rejection processes, the maximum values of macro parameters and pressure fluctuations, and the transitions of flow patterns have obvious differences because of these different initial rotational speeds.