Evolution and influence of high-head pump-turbine cavitation during runaway transients

Abstract

Pumped-storage hydropower stations (PSHSs) play irreplaceable roles in promoting the stability and flexibility of power grids. Runaway process is one of the most dangerous transients for PSHSs, and the cavitation in the pump-turbine seriously affects the stability and safety of the unit. However, the evolution and influence of pump-turbine cavitation during runaway transients are still unclear. In this study, the runaway transients of a high-head pump-turbine considering the cavitation effects were simulated by using the three-dimensional (3D) computational fluid dynamics (CFD) method. The results show that the cavitation cavities in the runner appear and disappear periodically, influenced by the backflows around the leading and trailing edges of the runner blades. The wedge-shaped cavities near the leading edges occur around the peak rotational speed moment when the pressure pulsations in the vaneless space show the peak magnitude. And the tongue-shaped shaped cavities near trailing edges appear around zero discharge moment when the hydraulic radial forces reach the peak. The two types of cavitation occur at dangerous moments, to which attention should be paid in the preliminary design stage of PSHSs.