Guidelines for acquiring high head Francis runner

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Forside Guidelines for acquiring high head Francis runner

This publication is a detailed technical buyer’s guide for HHF runners.

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The design criteria’s of yesterday do not fit tomorrow’s need of flexibility. Therefore, the knowledge gained from the High Head Francis project is of high value for the development of tomorrow’s high head Francis turbines. This publication is a detailed technical buyer’s guide for HHF runners.

Hydro power plants in Europe will have to operate with increased flexibility due to the future introduction of large amounts intermittent energy sources such as wind and solar. Norwegian hydro power plants are already operating with high flexibility due to the deregulated electricity marked and to the introduction of wind energy. This results in fatigue damages and it is the cause of several incidences of damage and break down of Norwegian High Head Francis turbines.

Over the last 15 years, several research initiatives involving Statkraft, NTNU, turbine manufacturers and others, have focused on the dynamic loads and resonance oscillations present during operation, to avoid crack growths and break downs on High Head Francis turbines.

Experience with HHF during the last fifty years has revealed some particular characteristics of these machines

⚈ A non-negligible fraction of these turbines develops cracks in the runner blades after relatively few operating hours
⚈ Change in operating pattern may also cause runners that previously had no issue to develop cracks
⚈ Cracks in one or a few blades is commonly identified as manufacturing issue
⚈ Similar cracks on all or most blades is normally understood to be a design issue

The tools that were traditionally used to analyse High Head Francis turbine runners seemed to have a large uncertainty, and statistics showed that there were more than 25% risk of crack failure on High Head Turbines in the period from 1990 to 2000. This was an unacceptably high risk, which had to be addressed by researchers through thorough numerical and laboratory work.

The HiFrancis-project has been carried out by NTNU and EDR Medeso in collaboration with turbine manufacturers, hydropower plant owners and technical consultants, and it has given a very good understanding of resonance problems in high head Francis turbines. The result is very much in the frontier of research on hydro turbine technology and it clearly show that the knowledge gained from this project is critical to secure flexible operation of Francis turbines. The results from the project is reflected in this guide.

This buyers guide gives a brief introduction to the technical design challenges for High Head Francis runners based on the results from the HiFrancis research project, followed by a detailed technical buyer’s guide for HHF runners.

This buyers guide is by no means a complete stand-alone technical specification for purchasing a high head runner. The scope of the Buyers Guide is by intention limited to only include technical aspects, mainly related to the HiFrancis project. Contractual terms (commercial, legal, administrative etc) are not included.