High head Francis turbines

The average age of Norwegian hydro power plants are 45 year, and many show sign of fatigue and needs to be constantly maintained or refurbished. Additionally, some power plants in Norway has experienced failures when installing new Francis turbines. The main problem is the formation of cracks in the turbine runner originating from high pressure amplitudes and/or resonance. The Norwegian hydropower industry have therefore addressed the risk of failure as a problem and want to see that the turbine manufacturers are capable of delivering turbines without formation of cracks before the end of the lifetime. Altogether, 9 utility companies, 4 turbine manufacturers, 3 consultants, Energi Norge, NVKS and NTNU are partners in this project. The main challenges for this project is to carry out model turbine measurements, which can be utilized to build a procedure for the numerical analysis of the Fluid-Structure Interaction (FSI) on high head Francis turbines. This procedure will reduce the risk for resonance and breakdown in future installation of high head turbines. The project will work with simplified models for the turbine runner and a complete Francis turbine model, and thorough measurements combined with FSI-analysis will be carried out. The flow conditions in a Francis turbine runner will be simplified and isolated in a blade cascade and the material properties such as the natural frequency of the runner will be tested with simplified geometry. The model of the Francis turbines at Tokke power plant will be utilized for the measurements. Here, steady state and transient operation of the turbine will be investigated. The main challenge is to carry out good measurements of the pressure and stress in the runner. Information and publications from the HiFrancis-project can be found here: www.ntnu.edu/web/norwegian-hydropower-center/hifrancis The measurements from the Tokke model turbine will be provided to other researchers through the Francis-99 workshops. The Francis-99 workshops aim to determine the state of the art of high head Francis turbine simulations (flow and structure) under steady and transient operating conditions as well as promote their development and knowledge dissemination openly. The final workshop took place at NTNU in May 2019. More information can be found here: www.ntnu.edu/web/norwegian-hydropower-center/francis-99

Statkraft har anslått verdien av denne forskningen til kr. 86 millioner. Dette er redusert risiko for havari i to kraftverk der de har bestilt nye turbiner. Det er utarbeidet en "Buyers guide - Guidelines for acquiring for high head Francis turbines." Denne skal benyttes av kraftselskap som skal kjøpe nye Francisturbiner, og den er vil redusere risiko for havari i disse innkjøp. NB. Minner om at det var perioder der man hadde 25% havari blant innkjøp av høytrykks Francis turbiner.

The Norwegian topography has enabled the development of high head power plants, many of which exceed 300-meter head. About 30% of all Francis turbines installed in such plants are located in Norway. Due to its national relevance and competence export potential, it is important for the Norwegian hydropower industry to maintain and develop its competence in this field. HiFrancis was born out of the need for further knowledge regarding a series of Francis turbine failures in the national grid. In the current market, turbines are operating at off-design operational conditions, and the industry is facing problems with both newly installed and old Francis units. The main problem is crack formation in the turbine runner, caused by pressure fluctuations. Computational Fluid-Structure Interaction (FSI) analysis are required to analyze the detrimental effect on the turbines. These are inherently complex and require huge amounts of CPU-time. As a conclusion from previous work, main challenges facing such analysis originates from the natural frequency of the runner and the fluid properties of existing pressure oscillations. Without tools for performing trustworthy FSI analysis, modifying high-pressure plants to for future use becomes risky and challenging. The following knowledge is required to develop tomorrow's high head Francis turbines: 1. Generic parameters needed for a FSI-analysis 2. Understanding fatigue loads during all states of operation. This will be achieved by 4 work packages where the main challenge in the research process will be to conduct the laboratory tests with sufficient quality for use as verification of numerical tools. These measurements include: 1. Pressure propagation speed and dampening 2. Natural frequencies of a turbine in operation 3. Velocities and pressure oscillations in a model turbine 4. Material stresses inside a runner Partners from turbine manufacturers, utility companies and consultants will assist the proposed tests and studies.