Abstract
Variable speed hydroelectric units equipped with full size frequency converter (FSFC) offer high operational flexibility enabling fast operating point transitions which increase grid regulation capacities. The XFLEX HYDRO H2020 European research project aims to demonstrate flexibility of such technology at prototype scale. The Z’Mutt pumping station, part of the Grande Dixence hydroelectric scheme located in Switzerland, is one of the demonstrators focused on the FSFC technology with a new 5 MW reversible Francis pump-turbine which will be commissioned in 2021. This paper, divided in two parts, aims to simulate the turbine mode fast start-up sequence made possible with the use of a FSFC and to assess the unit damage by means of 1D and 3D CFD simulations. The part I of this paper presents the 1D hydraulic transient simulation results of start-up sequences of unit U5 considering both conventional fixed speed technology and variable speed technology. The time evolution of the unit’s operating point is used as input data for 3D CFD simulations of part II, aiming to assess the impeller damage. Different control strategies to use the FSFC for turbine mode start-up sequence are analysed. Advantages and limits of each strategy are discussed, and recommendation is made for the Z’Mutt prototype demonstrator.
Highlights
The increasing contribution of intermittent new renewable energy sources in today’s electricity mix emphasizes the importance of balancing resources in modern power grids
A new 5 MW reversible pump-turbine, planned to be commissioned by 2021, is equipped with a full-size frequency converter, full size frequency converter (FSFC) and will be utilized in the XFLEX HYDRO project to assess flexibility offered by this technology
This optimization will be achieved by model tests (EPFL Technology Platform for Hydraulic Machines), 1D transient hydroelectric simulations (Power Vision Engineering), 3D CFD simulations and prototype field tests (HES-SO Valais-Wallis)
Summary
The increasing contribution of intermittent new renewable energy sources in today’s electricity mix emphasizes the importance of balancing resources in modern power grids. To avoid premature fatigue of mechanical components, these transition phases will be optimized in the framework of the XFLEX HYDRO project to maximize the unit life-time This optimization will be achieved by model tests (EPFL Technology Platform for Hydraulic Machines), 1D transient hydroelectric simulations (Power Vision Engineering), 3D CFD simulations and prototype field tests (HES-SO Valais-Wallis). The unit U5 of Z’Mutt power plant is taken as test case and comparison of impeller damage between conventional fixed speed technology and FSFC based variable speed technology will be performed. Between both technologies, different operating point evolutions with different durations are experienced. These trajectories are used as input data for 3D CFD simulations of part II
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