Simulation of a booster pump and a reversible pump turbine in series
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When considering whether to install a reversible pump-turbine instead of a new Francis turbine in a hydropower plant, the economic aspect is a key factor. The expensive process of submerging the runner, which is needed to avoid cavitation during pump-mode, is essential when calculating whether a reversible pump-turbine is profitable. In this thesis, the possibility of sidestepping the submergence of the runner by installing a booster pump in the forefront of the reversible pump-turbine is investigated. Results in this thesis are from 1D simulations using the method of characteristics to describe the fluid flow, with the pump performance of an axial flow pump and a reversible pump-turbine modelled by both Suter characteristic curves and dynamic pump models. Additionally, an investigation of how the two pumps operate when implemented in an existing hydropower plant, as a replacement for the Francis turbine in Roskrepp hydropower plant was simulated. Results from the implementation of Suter characteristics curves showed a steady cooperation of the two pumps. Furthermore; positive conclusions can be taken from the simulations of dynamic pump models implemented in Roskrepp which resulted in a steady combined operation able to adapt to forced alterations to the boundary conditions. A start-up operation of the two pumps was similarly simulated in Roskrepp, reaching steady state conditions without significant complications after an initial period of start-up fluctuations. Positive simulation results for the cooperation between a booster pump and a reversible pump-turbine provides an optimistic outlook on the idea.