Repairing a Francis turbine wheel requires specialist skills that can be found at HYDRO Exploitation’s Central Workshops in Martigny.
In a hydroelectric power plant, water drives the turbine wheel to generate electricity. But this is not without consequential damages. The sediment in the water creates an abrasive effect where the surfaces meet. There is also the cavitation phenomena resulting from the transformation of water into gas through depression. The parts are gradually worn away and need to be repaired.
Evaluation, machining, welding, grinding and non-destructive testing
Servicing a Francis turbine wheel is a complex procedure involving numerous stages. After various measurements have been taken to assess the repairs, specially designed templates are used to evaluate the differences between the original profile and the current profile. This is then followed by various stages of machining, welding, grinding and non-destructive testing.
Large digitally controlled machines take care of the machining (lathes and CNC milling machines) with an accuracy of 0.02 mm. This work requires careful attention because the slightest mistake can have huge ramifications.
Work on hidden areas using mirrors
Even with all the new technologies available, some of the grinding and welding must still be done by hand. This kind of work requires a certain know-how, concentration and precision in order to recreate the original profile of the turbine wheel as accurately as possible within 0.1 mm. The operator cannot even see some of the areas that need to be worked on; in this case a mirror is used to perform the necessary operations.