Successful Development Work for Offshore Wind Turbine



The new 5-MW wind turbine incorporating MULTIBRID technology is unique. Worldwide, it is the first facility of this performance class designed to withstand the harsh operating conditions on the high seas. Its official inauguration will take place in Bremerhaven at the end of May. FAG developed the rotor bearing for this huge wind turbine within just eight months; bearing manufacture took another six months. It is the largest and heaviest single rotor bearing that has ever been built by FAG.

The entire wind turbine has been specially designed to cope with the arduous conditions in the North Sea. Some 45 kilometers north off the island of Borkum, these are above all characterized by strong winds and salty air. Long maintenance intervals are required since repair and maintenance work at sea is not only costly but also extremely difficult to carry out.

So the FAG main rotor bearing has an extremely robust design and offers high load carrying capacity to reach the demanded service life of 20 years and more. The bearing boasts several superlative characteristics. It has an outside diameter of 3,200 mm, a bore diameter of 2,620 mm and a width of 485 mm. Its weight exceeds 7,200 kilograms. All bearing rings and rolling elements are manufactured from high-grade rolling bearing steel. The bearing is equipped with a steel-pin cage which permits almost full complement fitting with rolling elements and has proved extremely reliable under the most adverse operating conditions, e.g. in tunneling machines.

Designed in accordance with the MULTIBRID concept, the turbine solution features a rotor hub that is directly supported by a large rolling bearing in the machine housing. The drive train is a compact integrated gearbox/generator unit. For reasons of reliability and long service life, the design engineers opted for very low generator speeds. To minimize detrimental effects of the rotor loads on the gearbox and generator, the customized double-row tapered roller bearing transfers these loads to the adjacent structure, bypassing the gearbox/generator units. The advantage of this concept is the significantly reduced weight. Thanks to the absence of the high-speed gear stage, the tower head has a comparably low weight of only 300 tons. This makes it possible to pre-assemble the facility on land so that the nacelle can be hoisted to the tower at sea with only one lift.

Designed by FAG in close partnership with MULTIBRID, the double-row tapered roller bearing features an O-arrangement and a large angle of contact. This ensures the wide distance of the pressure centers enabling the accommodation of all loads and moments from the nearly 60-meter rotor blades. The bearing is clearance-free and slightly preloaded for optimum load support. An oil circulation system is used for lubrication. When the oil has passed through the bearing, it is filtered before being returned to the bearing and gearbox. Any contamination must be avoided for the sake of durability. Better oil quality leads to longer oil life and at the same time extends the service life of the bearing.

To ensure the economic maintenance of the facility, a condition monitoring concept was drawn up in cooperation with the FAG subsidiary FAG Industrial Services (F’IS). This provides for continuous monitoring of vibration, temperatures and movements in the bearing locations via numerous sensors. Any readings deviating from the specified norm are evaluated by experienced specialists and remedial action is taken to avoid unplanned downtime. All these measures serve to enhance turbine safety and provide maximum economic efficiency for the customer.

Next year, more wind turbines are planned to be erected on land and will be brought the “Borkum-West” offshore wind farm after successful functional testing.


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