Most wind turbines use gearboxes to transform the relatively low rotational speed of the main shaft into the higher speeds required for power generation. Single or two stage planetary gears are often used to keep the overall size small.
The bearings of the planetary gears tend to be highly loaded in this application. Austrian bearing specialist NKE Austria has developed a modular bearing system that will manage the loads better than other approaches. The system is already in use in the 1.5 MW, 2 MW and 2.5 MW wind turbine gearboxes of a well-known German gearbox manufacturer.
Schematic cutaway drawing shows the two stage planetarygearbox with one spur gear stage (source: Romax/NKE)
The modular concept is based on single-row cylindrical roller bearings of the RN range, which do not have an outer ring. These bearings are equipped with a one-piece solid brass cage, which is guided by the inner ring. The cage features inspection grooves for endoscopic inspection of the inner raceways as standard.
These single row bearings can be assembled to sets of two, three or four bearings to conform with the individual load and design parameters of a specific gearbox.
The tightly toleranced overall height of each individual bearing and their precise matching ensures even distribution of the radial loads. Each bearing set includes the components required to secure the bearings axially in the planetary gears – such as retaining rings and loose rib rings. If required, the overall width of each bearing set can be adapted to the operating conditions and the available space with spacer rings fitted between the individual bearings.
Fourfold planetary gear bearing set.
Used consistently throughout the gearbox assembly, the modular concept has several advantages: simpler design of planetary bearings; a standard bearing design for the first and second gear stage and across various gearbox sizes; reduction in the number of bearing variants; simpler adaptation of bearing set characteristics to the requirements of each gear stage; excellent rolling element guidance, due to the one-piece solid brass cage, even during rapid acceleration; and standard lubrication grooves to improve the lubrication of the planetary gear bearings.
NKE Austria GmbH