The elephant in the wind turbine
The reliability of a wind turbine is highly dependent on tribological issues associated with blade pitch systems, main shaft bearings, yaw systems , gearboxes, and generators. Many of the failure modes that occur in these systems such as fatigue, adhesion, abrasion, corrosion, fretting corrosion, polishing, electric discharge, and scuffing are influenced by tribology. Lubricant base oil, additives, and cleanliness must be correctly specified for each of these systems to achieve their design life. Currently, bearings in blade pitch systems, main shafts, yaw systems, gearboxes, and generators suffer early failures despite well maintained systems, proper lubricant selection, and clean oil. Furthermore, micro-pitting continues to attack gear teeth and bearing components. False brinelling and fretting corrosion are the primary failure modes for blade pitch and yaw bearings, and electric discharge is often the root cause of failures of generator bearings. Lubricant contamination by solid particles is a principle mechanism that causes debris dents on bearing components. These eventually lead to micro-pitting and macro-pitting. A recent critical bearing problem manifesting as axial cracks is occurring primarily in the inner rings of bearings, though also sometimes in outer rings. Currently, there are several controversial hypotheses for the root cause of this failure mode, but none of the hypotheses have been widely accepted across the entire tribology community.