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| Wind Turbine Generators |
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Wind turbine generators always work in the wild with relatively mal-conditions and this requests a good performance of bearings. Therefore, the structure, material, manufacture, lubrication and seal of bearings must undergo specialized design. Bearings for wind turbine generators mainly include the yaw bearing unit, bearings for main shaft, bearings for gearbox, and bearings for generator, etc.
The yaw bearing unit is a guarantee to fans for timely tracking changes of the wind direction. When the wind turbine generators begin to deflection, yaw bearings will come under greatly impulse force, and if the fan deflects in the course of campaign, the yaw gear will carry a large gyro moment, which can easily cause the yaw bearing fatigue failure. According to stress features of the bearing for wind turbine generators, “zero-clearance” four-point contact ball bearings are widely used in yaw bearings. Designing and manufacturing of this bearing’s groove should be specialized. In addition, suitable material, modulus and profile of gear tooth and hardness of the tooth face should be designed for the yaw gear in order to ensure the match of lifetime with the drive gear wheel. Meanwhile, specialized heat treatment measures should be taken in order to improve hardness of the tooth face. Hence, wear-resisting property and resistance to impact of bearings can be improved greatly.
Main shaft of fan blades are supported by two spherical roller bearings and have a good self-aligning performance. Main shafts in large wind turbine generators, whose stress condition is complicated, play an important role in carrying the blade and transferring torque that the blade suffered into the overdrive system. The forces on bearings for main shaft will change as the wind power changes and this will produce vibration, so it’s difficult to precisely calculate the load they carried.
There are many types of bearings in the gearbox and most of these bearings are lubricated by gear oil in the gearbox. Too much prill in luboil greatly shorten the lifetime of bearings. Therefore, special heat treatment should be used in order to producing compression stress on the surface of raceway, reducing sensitization of the raceway to prill and prolonging the lifetime of bearings. According to the work condition, it’s important to take further optimization of design and improve processing methods so that the performance index of bearings can be advanced.
Cylindrical roller bearings and deep groove ball bearings are used in the bearings for electric generator. Research indicates that the noise and vibration produced in the process of bearings operation predominant issue from geometric defects of bearing parts, waveness of raceway, roundness of rolling element in raceway, surface roughness of raceway and rolling element, etc. With the purpose of controlling the N&V of bearings, some measures such as optimization technical parameter of inner bearings, improving accuracy of manufacture and design of every bearings, mastering cleanliness in the way of transportation must be taken. In addition, the shaving of rollers and the choice of cages are also of account.
The actual performance after bearings mounted on host machine has a reference to not only the self-performance of bearings, but also the working conditions of adjustment. In consequence, the fitting form of adjustment and the center align should be researched so that bearings have a good working performance in actual use. |
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