Hydropower turbines are subjected to enormous forces and damage mechanisms. Over time, erosion and cavitation lead to major efficiency losses and a marked reduction in useful lifetime. To hinder this, turbine manufacturers rely on hightech coatings from Oerlikon Balzers and Oerlikon Metco.
The demand for energy is constantly increasing, driven by population growth and increasing prosperity in emerging countries. One of the most environmentally-friendly types of energy generation is the use of hydropower – using run-of-river hydropower plants placed directly in the river course which constantly generate power, or pump-storage power plants (e.g. reservoirs), which are used to store energy for release upon demand – a function of ever increasing importance.
Power plant operators are focused on ever higher turbine economic efficiency, through extended useful lifetime, longer inspection cycles and higher efficiency. At the same time, a growing number of new waterways, previously deemed too inaccessible, are now being tapped – often highly sandy rivers or waters with high head. Wear protection for individual power plant components is thus a key factor for the success of these projects.
Oerlikon Metco provided the first coatings for Francis turbines in the 1930’s, and, since the 1980’s, has protected thousands of turbine runners in hydropower plants throughout the world with its thermal spray coatings, which can be up to 400 μm (0.4 mm) thick. The coatings are individually tailored – they are dependent on machine design, precise operating mode and specific operation conditions.
Oerlikon Balzers is, then again, a specialist for extremely thin PVD coatings. Not just cutting tools used to manufacture turbine parts are coated with BALINIT, but also bearings or valves in the overall system. The goal of both applications is to reduce wear caused by friction and thereby to increase efficiency.
The right coating not only enables extended service life, but also longer inspection cycles and higher efficiency. Both turbine design (Pelton, Francis, Kaplan) and operating conditions are crucial factors for the customization process. Pelton turbines are, for example, used in areas with high head (more than 100 metres) and small water quantities. In the opposite case – namely with lower head and large water quantities – a Kaplan turbine is generally used. The design of the latter makes it more susceptible to destructive cavitation, which affects both the choice of coating and the turbine parts to be coated. The choice of wear protection must also consider not just the amount of silt, sand and shingle that is carried along with the water, but also chemical contamination.