All the forces from the wind act directly on the rotor bearing support in a wind turbine and the rolling bearings are therefore subjected to highly dynamic loads and operating conditions. A range of powertrain designs have established themselves on the market, each of which requires a different bearing support. Schaeffler has therefore optimized proven bearings and, at the same time, developed new bearing designs for various bearing support concepts.
FAG flanged bearing unit: Compact and easy to mount
Schaeffler has developed a new, compact bearing unit for moment bearing concepts in rotor bearing supports: 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 O arrangement, with grease lubrication and seals, is supplied pre-assembled. The inner rings are flange-mounted to the rotor while the outer ring is flange-mounted to the nacelle. The bearing clearance is preset and this significantly reduces the logistics and mounting costs.
FAG GreaseCheck: Grease condition monitoring during operation
As an option, the flange-mounted tapered roller bearing unit can be fitted ex works with FAG GreaseCheck. The grease sensor is parameterized to the specific type of grease and provides optical measurement of the water content, turbidity and mechanical wear, as well as the grease temperature directly, in the bearing support. An analysis unit, which is connected by a cable, generates information on the condition from the measurements and transmits them as an analog signal. If GreaseCheck detects that the water content in the grease has exceeded a defined threshold, it can typically generate two responses: It can send information to the control room so that plans can be put in place for an inspection and, if necessary, a replacement of the seal. Alternatively, the signal from the grease sensor can communicate with the central lubricating system via the control room so that the bearings are relubricated at shorter intervals and in greater quantities in order to improve the condition of the grease in spite of the damage to the seals and to protect the bearing from damage due to grease failure.
ASTRAIOS: Simulation models and test runs provide mutual optimization
Schaeffler’s own large-size bearing test rig ASTRAIOS contributed to the development of the flange-mounted tapered roller bearing unit: While rating life calculations from smaller rolling bearings transfer well to large-size bearings, this is not so much the case for other parameters such as kinematics or frictional torque. Simulations in these areas must be therefore validated by test results. The measurements are fed back into the simulation models in a multi-stage process so that they can calculate the loading and the kinematic behavior of a large-size bearing. If, for example, only deformation is calculated, then its effect on the function of the rolling bearing can be simulated and validated on the test rig. Ever since ASTRAIOS was put into operation in 2011, it has been supplying important information on features which could previously not be tested, such as sealing and lubrication concepts, operating clearance (influence of the temperature and connecting screws) and roller speed.
FAG spherical roller bearings: More robust than ever
In order to increase the reliability, availability and therefore the economy of wind turbines, Schaeffler has optimized its spherical roller bearings for main rotor bearing supports. This bearing design is used exclusively on the so-called shaft bearing support – the most frequently occurring bearing support concept. In order to optimize the bearing, both its micro and macro geometry were addressed. The result is conclusive: It was possible to reduce friction and pressures in the bearing, to improve the distribution of forces, and to increase the axial rigidity. These optimized spherical roller bearings, therefore, have greater resistance to the wear which specifically occurs as a result of axial displacement. These 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).
Asymmetric FAG spherical roller bearings: New design for improved load distribution
This asymmetric design represents a significant step forward. It substantially increases the axial load carrying capacity and thus 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 produced improved load distribution, lower contact pressures and a significant reduction in the axial displacement.