Abstract: This paper explores the cause of power oscillation and analyzes its relationship with system parameters through a case study of the power oscillation of generating units at Bailianhe pumped-storage station in generation mode under the conditions of low heads and large valve openings. First, we construct a one-dimensional numerical model for time domain analysis including the calculation of draft tube cavity vortices; then, the method of characteristics is used to solve the model with its simulations compared with measurements. Finally, we conduct a sensitivity analysis of the relationship between cavity vortex parameters, governor parameters, peak opening and closing speeds of guide vanes, regulation mode, and power oscillation. The results show that the power oscillation is caused by the cavity vortex rope, while governor parameters or peak opening and closing speeds have little effect on its occurrence under the influence of the cavity vortex. And it mainly depends on the cavity compliance and the mass flow gain factor of the cavity vortex rope. Thus, the results lay a theoretical basis for safe operation of pumped-storage stations.

Key words: pumped-storage power station, power oscillation, method of characteristics, cavity vortex parameters, regulation mode