All About Wind Turbine Bearings

Bearings are an important component used in wind turbine operation, and they are often utilized in the main shaft. There are two integral bearing variations that you will come across within the main shaft of a wind turbine— spherical roller bearings and tapered roller bearings.

Spherical roller bearings (SRB) are usually used in single SRB designs, where a 3-point mount system is supported by one main bearing. Because the main bearing can take some of the load, two torque arms are designated to carry gearbox reaction stressors and loads. Failures of this mechanism occur because of two occurrences—application of too much thrust, or inadequate lubricant generation. Regular maintenance concerning the former issues is extremely important, as full replacement of a main shaft and its bearings can cost upwards of $450,000.

Tape bearings (TRBs) are designed to improve the powertrain performance of the turbine. They are engineered to provide increased stability to the main shaft through a load sharing construction of rows, and predicted roller-to-race interactions. There are three main types of TRBs, including: widespread single TRBs, large diameter TRBs, and single preloaded TRBs.
           
A widespread single TRB is considered economic in design because of its compact size and its ability to preload a whole turbine system using just two TRBs. The system can adjust bearing capacity through an upwind and downwind series. These components act like bookends to the widespread center between the two bearings. The series manages applied load by adjusting the contact angle when necessary.
 
A large diameter tapered roller bearings, sometimes referred to as a TNA bearing, is most often seen on direct-drive wind turbines. It is known for its easy set up and has excellent ratings for field performance. This component utilizes a spacer unit that is placed between two cone races at a steep angle. The angle of the cones creates what is called high tilting stiffness within a compact axial design, allowing the turbine manufacturers to reduce overall nacelle length if necessary.
 
A single preloaded TRB can manage higher radial loads and thrust loads than an SRB. It utilizes two bearing rows in order to evenly distribute load sharing. Because of its design, this mechanism is able to accommodate higher load capacities and has the capacity to tolerate greater system misalignment.