The leading rolling bearing manufacturer FAG Kugelfischer is once again presenting itself as a competent systems partner for all types of bearing arrangements in wind power plants.

Nearly all manufacturers of wind turbines or gearboxes rely on the experience of FAG in the development of new generations. The services rendered to this growth industry range from the development of new concepts via design and mounting support through to the maintenance and monitoring of bearings in wind turbines.

Rolling bearings in wind turbine drive trains support the rotor, the gearbox and the generator. The control unit incorporates slewing bearings as well as bearings in the blade adjustment of pitch-controlled wind turbines and in the gearbox motors that drive the turret and pitch control. All in all, the rolling bearings in a wind turbine account for approx. 3.5 percent of the total production costs. This proportion is likely to increase in the near future, for instance due to the integration of rotor and gearbox bearings in the multi-MW class.

The development of new wind turbines brings with it new challenges. Rolling bearings in such applications are subjected to unusual stresses and operating conditions that have not been fully explored to date. FAG engineering experts pursue basic research in this field and develop new solutions in cooperation with their clients.

Rotor bearings
Rotor bearing arrangements consist of two bearing locations - locating and floating bearing or adjusted bearings. In many cases the input shaft bearing of the gearbox is used as floating bearing of the rotor. The extensive FAG catalog range of products ensures that the majority of applications can be covered with standard bearings. Necessary customized designs, such as the complete connection of the rotor bearing to the gearbox, are developed in close cooperation with the user. Multi-MW offshore turbines incorporate rotor bearing units of two large bearing series at a relatively small distance. The outside diameter of such bearings can amount to more than two meters in a 3-MW turbine. An integrated rotor and gearbox bearing permits a short overall length.

FAG also develops and manufactures the bearing arrangement housings. FEM calculations ensure the optimum accommodation of loads and moments with as few material requirements as possible. In addition FAG offers lubricants, sealing and other accessories from one source. In this way all elements fit smoothly into the overall system rolling bearing arrangement.

Gearbox bearings
The rolling bearings in the gearbox represent the link between shafts, toothed gears and housing. Failures of these components directly lead to rolling bearing damage. Thanks to F'IS (FAG Industrial Services) monitoring technology, even slight changes can be recorded and diagnosed long before actual damage occurs so that maintenance activities can be planned early on.

This monitoring technology has been especially adapted to the specific requirements in wind turbine applications, as the prevailing operating conditions cannot be compared to those in stationary gears. They are characterized by strong dynamic influences with extreme peak loads, strong load alternations, light loads with high percentages of time and extreme temperature variations. Rolling bearings are exposed to dynamic wind loads via the rotor on the one hand and to the dynamics of the electrical grid via the generator on the other.

Deformation of the gearbox housing places additional stress on the bearings. Peak loads also result from fast braking processes triggered by the high-speed brakes. Developed only recently, the simulation calculations of the dynamic behavior of the drive train will lead to complete load formulations and supplement the former formulations of analogies and measurements.

Bearing monitoring
The monitoring of bearing vibration in wind turbines permits the avoidance of unplanned downtime, identification of damage at an early stage and observation of the damage progress. Emergency shutdowns are triggered in the event of previously defined conditions, thus preventing follow-up damage. Service and maintenance can be carried out as planned. Remote monitoring and online data transfer are state-of the art at FAG/F'IS and prove attractive particularly for offshore turbines that may not be accessible for months. The costs for hardware and monitoring through FIS specialists make up just a fraction of the costs of gearbox damage - not to speak of unscheduled machinery downtime.

Lubrication
The reliability of bearings largely depends on the lubricating system, the quality of which is characterized by the efficiency of the lubricating oil, effect of additives and lubricant cleanliness. Part of the problems observed are clearly attributable to lack of lubrication. This experience has led to demands for efficient filter systems and condition-monitoring of important lubricant parameters, such as operating temperature, contamination, water content and viscosity.

Service
When it comes to selecting the most economic bearing arrangement, FAG attaches great importance to comprehensive advisory service. This includes the calculation of the bearing with the help of the "Bearinx" calculation program and advice regarding the design, mounting and lubrication of the bearing. Program packages with calculation possibilities as well as attractive and graphically supported result printout are indispensable in dimensioning and documentation.

In addition, a detailed analysis of running and damage characteristics provides important information for future improvement potential. This is why FAG and F'IS offer their customers not only the visual examination through experts but also thorough investigations with the scanning electron microscope as well as x-ray fine structure analyses and examinations of the lubricant.

The dimensions of the rolling bearings will grow in relation to the output of the wind turbine. Mounting therefore requires even more care and experience. For this reason, FAG and F'IS offer a worldwide mounting service by experienced fitters or certified service partners for the inspection of surrounding parts as well as mounting and dismounting, inspection and maintenance. In brief - FAG and F'IS undertake everything to offer their clients extra operational reliability.




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