Austrian bearing manufacturer NKE introduces modular bearing systems for planetary gears in wind turbine gearboxes that offer the advantages of a standardization of the bearings used in this application, reduced diversity of parts and simpler logistics.

Since the bearings of the planetary gears are among the highest-loaded in the single- or two-stage planetary gearboxes many wind turbines are equipped with, integrated bearing assemblies have specific advantages. NKE's bearing systems consist of cylindrical roller bearings that are fitted directly into the planetary gear. The bore of the gear acts as the outer raceway, so the bearings themselves do not have an outer ring.

The bearing systems are developed to customer specifications. For gearboxes rated 1.5 MW, 2 MW and 2.5 MW, NKE has achieved projects with modular systems consisting of single-row cylindrical roller bearings without outer race. The bearings have bore diameters of 160, 190 and 200 mm, with versions up to 220 mm currently under development. Choice of bearings depends on the available space, as well as customer requirements. To further boost load capacity, the cylindrical roller bearings feature an improved internal design that is stronger than that of the standard types.

These bearings are fitted with an inner race-guided, one-piece brass cage, which contains inspection grooves for endoscopic condition assessment of the inner race surface as standard. For higher loads and wider gears, the bearings can be assembled to sets of two, three or four bearings.

The modular concept has several advantages: the designs of the planetary bearings can be standardized; the planetary gear design can be unified for the first and second gear stage and across various gearbox sizes, which reduces the required number of rolling bearing variants; the modular design simplifies the adaptation of bearing set characteristics to the requirements of each gear stage; the one-piece solid brass cage provides high rolling element guidance even during rapid acceleration; and the lubrication grooves provided as standard simplify lubrication of the planetary gear bearings.