Departments - Design Diagram
Bearing the weight of the rotor shaft
2/15/2010
Bearings are highly engineered, precision components that enable movement at high speeds and are utilized in gearboxes, generators, cooling systems, blade pitch and yaw systems, rotor support systems, and more.
Bearings are highly engineered, precision components that enable movement at high speeds and are utilized in gearboxes, generators, cooling systems, blade pitch and yaw systems, rotor support systems, and more. In addition to being high quality, they must be corrosion resistant in order to prevent premature failure.
Strength and rotor shaft arrangement is of great importance due to the force of movement induced by the wind. Roller bearings are subjected to highly dynamic loads and operating conditions.
When looking at rotor shafts in wind turbines, a locating or floating bearing arrangement with spherical, cylindrical, or tapered roller bearings has been the typical shaft bearing arrangement. A hub bearing arrangement typically contains two tapered roller bearings, with an alternative design being that of a locating/floating arrangement that is comprised of a matched tapered roller bearing and a cylindrical roller bearing.
Increasing in design implementation is the moment bearing arrangement that uses a large double row taper roller bearing that effectively removes the need for a main shaft. These designs combine the force and moment support functions in a multi-row rolling bearing with the design as a double row tapered roller bearing matched to the operating conditions.
Other increasing shifts in design are toward tapered and cylindrical roller bearings in today’s large megawatt turbines, which provide the greatest performance potential in the most compact design possible – reducing system size, weight, and manufacturing costs.
New Look
Sweden-based SKF Group offers up a different look at their bearing design for the ever-increasing size of turbines. A 5MW, three-blade turbine, with a rotor diameter of 413ft has speed range varying between 6.9rpm to 12.1rpm. The windmill employs a combined planetary/spur wheel gearbox, with all bearings lubricated directly by oil systems that include effective filtration. The machine compartment, or nacelle, base frame is connected to the tower by a four-point contact slewing bearing, and held in position by brake calipers. Geared electric motors turn the nacelle into the wind. The machine’s huge rotor weighs more than 100 tons, which exerts tremendous loads on the rotor shaft.
The design of a bearing system for this giant wind turbine with an unusual rotor shaft has led to the development of the CARB toroidal roller bearing system, as well as to advances in bearing assembly techniques, and axial fixation methodology for large bearings. The CARB toroidal roller bearing has an inside diameter of 4.9ft, weighing 5,950 lb for the rotor assembly. Typically, one bearing supports a rotor shaft on most wind turbines – the other being in the gearbox – however the shaft in the 5MW unit has two. The CARB toroidal roller bearing is in the non-locating position and a spherical roller bearing is in the locating position. Thus, the gearbox bearings only have to carry torque loads, resulting in this rotor bearing design offering high load capacity, low weight, and the capability to accommodate misalignment.
A look at various bearing suppliers for the wind turbine industry:
American Roller Bearing Co., amroll.com
Avon Bearings/Kaydon, kaydon.com
Bartlett Bearing Co. Inc., bartlettbearing.com
Consolidated Bearings Co., consbrgs.com
Glebus Alloys LLC U.S.A., glebusalloys.com
IMO Energy GmbH & Co. KG, imo.de
Kaman Industrial Technologies, kamandirect.com
Midpoint Bearing, midpointbearing.com
Motion Industries, motionindustries.com
NKS Corp., us.nsk.com
Rotek Inc., rotek-inc.com
Schaeffler Group U.S.A., fag.com
SKF U.S.A. Inc., skfusa.com
Timken, timken.com