Drive train concepts and main shaft bearing solutions; Current concepts and challenges of Multi-MW offshore turbines

Philipp Schmid 1, John Skiller3, Matthias Hofmann1, Andreas Urban2, Steffen Beck1
1SKF Gmbh, Schweinfurt, Germany, 2SKF, Steyr, Austria, 3SKF, Nieuwegein, The Netherlands



A new generation of offshore turbines up to 8 megawatt category has now been introduced. These turbines have a hub and blade weight exceeding 200 tonnes and are required to operate reliably under harsh conditions. The overhang from hub to tower center is relatively large to provide adequate space for the bending blade tips. A challenge for this large turbines is to develop drive trains which are able to carry the huge loads which are a result of the weight. On the other hand they should be as light and as compact as possible in order to reduce the total cost of the machinery and of installation. Needless to say that reliability is of outmost importance for an offshore turbine.



In an overview different drive train concepts and main shaft bearing arrangements will be discussed which are suitable for Multi-MW offshore turbines.  Those arrangements are Spherical roller bearings in geared turbines, rigid bearings used in geared turbines as well as SKF Nautilus bearings in either geared turbines or direct drives. Criteria are weight, compactness load capacity as well as possible deformation of housing and shaft.



There is no established consensus regarding an industry standard for Multi-MW offshore turbine design and hence bearing arrangements for these turbines differ. The solutions are driven by the particular nature of the turbine architecture and operational requirements.

The range of different drivetrains will evolve further in the future. Bearings for 8+ MW turbines will need not only bearings with even higher load ratings (which can be reached for instance by bigger rollers and ring cross section) but also other features combined together in the bearing system to ensure reliable rotating equipment performance.



Extensive testing will be essential for future development. Therefore SKF has invested in a first test rig which will be capable of testing not just a single main bearing but a complete rotor bearing arrangement. Using these exceptional capabilities, SKF wants to simulate extreme dynamic loads of the order of several MN or MNm in as realistic a manner as possible. The test rig can subject structures of that kind to dynamic forces in all directions that, when combined, are many times greater than on the strongest test installation currently available.



Bearings are a critical component for wind turbines and highly affect reliability of the system. Participants will get an overview on current technology and will be able to identify critical parameters for drive train concepts and bearing arrangements.

Further they will learn about system criteria for the best practice design of a main shaft bearing arrangement.