Development of a reliable very high-head pump turbine considering challenging hydrodynamics

This article describes the development of a reversible single-stage pump turbine for a new power plant with a maximum pump head of roughly 750 m, a specific speed of n_q = 34 and a ratio of maximum to minimum head including surge tank fluctuations of 1.57. At this plant the water systems of two existing hydro power plants are connected by means of additional water tunnels. Therefore the plant's water system features an upstream as well as a downstream surge tank. The hydraulic design of the pump turbine focuses on robust and stable operation under consideration of the complex hydrodynamics of the system of power plants while maintaining a very high level of pump and turbine efficiency and maximum operating flexibility. State-of-the-art numerical simulations of the flow behaviour at design and off-design conditions have been applied to predict the hydraulic behaviour during the design phase. These results are compared with experimental data from the model tests. From the agreement between simulation and experiment it is concluded that the application of modern simulation techniques in combination with design experience allows for successful developments also for projects within very challenging hydrodynamic boundary conditions.