Several bearing configurations for wind turbines come from NTN Bearing Co. of America, Mt. Prospect, Ill.
For instance, for main shafts, designs include spherical roller bearings. The company says these increase efficiency and service life. Credit for that goes to new materials and improved heat treatments that significantly increase overall bearing service life. The company manufactures all sizes of mainshaft bearings, from designs for common 1.5-MW turbines to the more recent 3.5-MW designs.
For generators, insulated bearings include the Megaohm Series. These are well insulated against electrical currents. Generators often produce stray currents that cause electrolytic corrosion which can shorten bearing life. To combat the problem, NTN’s ceramic-coated Megaohm ball bearings insulate themselves from electric current. A ceramic coating applied to the outer surface and sides of the outer ring prevent current from passing though the bearing. The ceramic provides an insulation resistance of at least 2,000 M-ohm under normal operating temperatures, alleviating electrical arcing and early bearing failure. Ceramic-coated bearings come with or without seals or shields, and are interchangeable with standard, non-insulated units.
For yaw gearboxes, tapered roller and angular contact bearings are compact designs with high-load capacities. A yaw gearbox rotates a turbine face to keep it into the wind. The gearbox here is generally small yet capable of transmitting high torque so its bearings must be compact and capable of high loads.
Lastly, main gearboxes, or speed increasers, turn the low-speed rotor into higher speeds for generators. These generally use cylindrical roller, tapered roller, and occasionally spherical roller and ball bearings. Cylindrical roller bearings for gearboxes have higher rigidity and lower friction than conventional bearings through reduced rolling element slippage.