AFC4HYDRO main objective has been to design and validate an Active Flow Control (AFC) system in actual hydraulic turbines that permits to operate at extreme off-design conditions and sustain more transients. For that, a consortium of two universities, Universitat Politècnica de Catalunya (UPC) in Spain and Luleå University of Technology (LTU) in Sweden, two of the Europe’s largest renewable energy producers, Vattenfall in Sweden and Statkraft in Norway, a Small and medium-sized enterprise, Flow Design Bureau (FDB) in Norway, and the Porjus Hydropower Center in Sweden, was created.
This innovative and affordable AFC solution, allowing an improvement of existing hydraulic turbines, has been validated at small scale in a model turbine and at large scale in three prototypes: i) one 10 MW Kaplan turbine located in Porjus (Sweden), and its homologous reduced scale model installed at the Vattenfall Research and Development Center in Älvkarleby (Sweden), ii) one 200 MW Francis turbine located in Oksla (Norway) and, iii) one 25 MW Francis turbine located in Svorka (Norway).
Different technologies have been combined to reduce the unsteady pressure loads exerted on the runners of Francis and Kaplan hydraulic turbines induced by the draft tube flow using: (1) protrusion of rods in radial direction (IPM system); and (2) injection of variable speed water jets with different orientation angles (ICM system). A structural health monitoring system (SHM system) has been developed to evaluate the effects of the IPM and ICM on the dynamic response of the runner, the shaft line, the generator, the bearings, the waterways and the supporting structures using on-board and off-board sensors. These measurements have been used to assess the suitability of a Controller to find the best actuation strategies in real-time operation to reduce pressure fluctuations, structural loads and induced vibrations. An AFC system tailored for full-scale prototypes has been tested against demanding off-design conditions such as speed-no-load (SNL), part load (PL) and load ramping where special attention has been be given to mitigate the powerful and dangerous flow instability provoked by the vortex rope breakdown.
With AFC4Hydro, existing turbines will extend their operating range beyond the stablished safety limits at PL, will face more operation at SNL and will be submitted to more frequent load transients with less wear and tear than before. Consequently, the application of this technology will reduce the maintenance and operating costs, improve performance, facilitate the integration of hydropower in the European energy system, increase the renewable power system flexibility, favour the circular economy and reduce the negative effects of the climate change.
