Fortum’s 10MW hydropower plant at Vassinkoski, Sweden, is now successfully operating with Thordon Bearings’ polymer SXL turbine guide bearing following the completion of the plant’s extensive renovation and recommissioning work.
Thordon’s involvement in the project followed the retrofit installation in 2013 of its water-lubricated bearings to the slightly larger Noppikoski plant, also in Sweden. Both refurbishment projects were overseen by ČKD Blansko Holding, the largest turbine manufacturer based in the Czech Republic. For both plants, ČKD Blansko specified Thordon’s SXL polymer bearings, each with a bronze tapered keyset, in addition to SXL axial sealing face rings.
Greg Auger, Thordon Bearings’ Hydro & Clean Power Business Unit Manager, said: “When we were first approached by ČKD Blansko to supply the new turbine guide bearing for the 1967-commissioned Noppikoski turbine, we were faced with a particular design challenge: the Francis turbine is connected to the generator by a 45m long shaft supported by seven individual bearing positions. The scope of the project was so extensive, it made sense for ČKD Blansko to replace all of these bearings to achieve the best control of shaft position and vibration.”
Water-lubricated guide bearings
While the six original oil lubricated bearings were replaced with new oil lubricated assemblies, only the one closest to the water was replaced with an SXL water lubricated guide bearing to support the 420mm (16.53”) diameter shaft. Thordon also supplied a longer wearing SXL seal face material for the axial seal assembly that was installed. This was Fortum’s first experience with Thordon’s water-lubricated guide bearings supplied as part of a major upgrade project. Based on the success of the retrofit and subsequent five-years of seamless operation, Fortum and ČKD Blansko specified a similar scope of supply for the Vässinkoski plant, which also operates a 1967-commisioned Francis turbine and generator.
“Aside from the obvious environmental advantages, the Thordon solution provides for a longer operating life and, due to the unique tapered keyset design, optimises in-service maintenance since the SXL polymer can be removed without having to split the bearing’s metal housing,” added Auger.
Working with ČKD Blansko to help design and build all the metal components, the companies were able to use parts of the original bearing casing but replaced the rubber element with the Thordon SXL polymer. During assembly, the bearing was submerged in liquid nitrogen at -196°C (-321°F) to ensure a perfect fit into the housing, but this meant engineers had only about ten minutes to install the bearing in its housing.
“Everything went very smoothly, indeed,” said Piroutek. "We anticipate the Noppikoski and Vässinkoski plants will now be operating for another 30-years before their bearings need to be replaced. During the commisioning ČKD Blansko technicians confirmed very negligible water leakage through the axial seal – even less than Thordon calculated during the design stage.
The Vässinkoski and Noppikoski hydropower plants, both located on Sweden’s Oreälven river, each operate one 10MW vertical Francis unit rated at 333rpm and connected to the turbine runner by a 45m long shaft. Following extensive tests, the Vässinkoski plant upgrade was commissioned in March 2018.