In a turbine, wind forces act directly on the rotor bearing support, meaning rolling bearings are subjected to highly dynamic loads and operating conditions. Several powertrain concepts have been established on the market, each requiring a different bearing support. Schaeffler has optimised proven bearings and developed new bearing designs for various bearing support concepts.
Schaeffler has developed a new compact bearing unit for moment bearing concepts in rotor bearing supports: the FAG flanged bearing unit. The flange-mounted tapered roller bearing unit allows all forces and moments in a bearing to be safely supported due to the large pressure angle and tight axial guidance of the rotor. The double-row tapered roller bearing unit in an 'O' arrangement, with grease lubrication and seals, is supplied preassembled. The bearing clearance is also preset, significantly reducing logistics and mounting costs.
The flange-mounted tapered roller bearing unit can be fitted with FAG GreaseCheck. The grease sensor is parameterised to the specific type of grease and measures changes in the lubricant directly in the bearing support.
If GreaseCheck detects that the water content in the grease has exceeded a defined threshold, for example, it can generate two responses: it can send information to the control room for plans to be put in place for an inspection and, if necessary, replacement of the seal; or it can communicate with the central lubricating system so that the bearings are relubricated at shorter intervals and in greater quantities. This improves the condition of the grease in spite of the damage to the seals and protects the bearing from damage due to grease failure.
In order to increase the reliability, availability and, therefore, economy of wind turbines, Schaeffler has optimised its FAG spherical roller bearings for main rotor bearing supports. This bearing design is used exclusively on the shaft bearing support - the most frequently occurring bearing support concept.
In order to optimise the bearing, its micro and macro geometry was addressed. The result was conclusive: it was possible to reduce friction and pressures in the bearing, improve the distribution of forces and increase the axial rigidity. These optimised spherical roller bearings therefore have greater resistance to the wear that occurs as a result of axial displacement. The bearings successfully completed a comprehensive range of tests as part of their validation for the Schaeffler 'X-life' quality seal. The validation steps required for this have been certified by Germanischer Lloyd (GL certificate GL-CER-002-2015).
The design of asymmetric FAG spherical roller bearings represents a significant step forward. It substantially increases the axial load carrying capacity and, therefore, the operating life of main bearings in wind turbines. It allows a larger contact angle to be used on the bearing row subject to axial loads, and a smaller contact angle on the bearing row subject mainly to radial loads. This has meant improved load distribution, lower contact pressures and a significant reduction in axial displacement.