Refurbishment of twin Francis turbines – maximizing the annual production

Abstract. Before the invention of the Kaplan turbine, Francis turbines were also built as twin Francis turbines. An example for such a single-regulated horizontal axis twin Francis turbine is the hydro power plant Meitingen – 3 units with an inlet chamber and a single-sided shaft led through. This plant, which is located on a diversion channel, went in operation in 1922 with a nominal power of 11.6 MW for the three machine sets providing an annual production of 72.6 GWh. Due to cracks and cavitation damages, one of the units should be replaced, yet, after a comprehensive study the decision for a major mechanical and electrical refurbishment was taken. The geometry was scanned on-site and a CAD model was generated. The RANS calculation for the whole power plant provided information on the overall performance, the losses referring to each component and the flow situation in each of the turbines. An optimization of the runner design was carried out and an increase of 14.8% of the annual production could be realized. All of the units were brought into operation after the refurbishment and the performance level was checked successfully by means of an on-site efficiency measurement campaign according to IEC 60041.