Low-friction bearings reduce energy losses in free-stream turbines

A hydro turbinecompany, based in Portland, Maine, in the US, has chosen Vesconite Bearings’lowest-friction material for the thrust bearings on its free-stream turbines.

The material, Vesconite Superlube, has one of the lowest coefficients of friction of any plain bearing material available, with a coefficient of friction lower than virgin polytetrafluoroethylene.

"Thrust bearings made from this material were first ordered in June 2022 and installed in November 2022," states renewable-energy application developer Petrus Fourie.

These initial bearing will be assessed in December 2023, but the client, which has been satisfied with how they were installed and how they have operated to date, does not anticipate any problems, he adds.

The company has also ordered additional sizes of Vesconite Superlube thrust bearings, so it is believed that the thrust bearings have now been installed in multiple devices.

The renewable-energy company wanted a water-lubricated bearing because of the environmental benefits of eliminating  grease from water systems.
It also required low friction, since this would reduce friction losses and therefore induce greater overall system efficiency, and low wear rates, ensuring that the bearings would last longer and require less maintenance.

Reduced maintenance is a desirable factor, owing to the difficulty and cost of doing maintenance on turbines that are deployed in the ocean or rivers, since they either float on the surface or sit at the bottom of a river or they are placed in the sea where there is high tidal flow.

"The thrust bearing rings rotate against a stainless steel counter-surface and absorb any axial loads on the main shaft of the hydro turbine,” describes Fourie.

"If any axial load is applied, the friction on the sliding surface results in a torque on the main shaft acting in the direction opposite to the rotation of the shaft, effectively braking the turbine and causing energy losses in the system. The energy losses [owing] to this effect are directly proportional to the friction coefficient, hence the importance of minimising friction to improve system efficiency."