Wind turbines are now one of the main sources of green power. In 2025 alone, wind turbines in Germany generated around 132 terawatt hours of electricity, accounting for a substantial share of the country’s public power generation. This underlines the important role of wind energy in the power system and shows how critical the reliable, long-term operation of these turbines is.

What is often overlooked is that this stable operation depends not only on the rotor and generator, but also on “invisible” components inside the drivetrain. Cylindrical roller bearings are one of these key components, especially wherever high forces must be transmitted continuously within the gearbox, shafts must be guided precisely, and gear meshes must remain reliably engaged.

From Rotor to Generator

The rotor initially converts wind energy into slow rotational motion. For compact generators that require a higher input speed, this rotor speed is too low. A multi-stage main gearbox therefore increases the speed to a suitable level.

Many wind turbines use multi-stage gearboxes for this purpose, often incorporating one or more planetary stages. This design makes it possible to transmit high power within a compact installation space while distributing the forces acting on the system across several components.

During operation, however, the gearbox is continuously subjected to fluctuating loads. These result, among other things, from wind gusts, blade pitch adjustment, grid influences, and vibrations originating from the tower and rotor. Such conditions place demanding requirements on the components.

For the gearbox to operate reliably over many years, it must run smoothly, stably and with minimal vibration even under changing wind conditions. The bearing arrangement plays a decisive role here, as it makes a major contribution to the smooth running and service life of the entire drivetrain.

Why Cylindrical Roller Bearings Make Such a Difference in Wind Gearboxes

Cylindrical roller bearings are particularly well suited for use in wind turbine gearboxes because they can reliably transmit high loads under heavily fluctuating operating conditions.

Their cylindrical rollers are in line contact with the raceway. This distributes the load over a larger surface area, reduces contact pressure under normal operating conditions, and allows load peaks caused by gusts or load changes to be absorbed more effectively. At the same time, their high radial stiffness helps shafts and gears maintain their position. As a result, the gears mesh evenly, the gearbox runs more smoothly, noise is reduced, and wear is minimized.

Optimized raceway profiles and a suitable cage design also support even load distribution and help prevent pronounced stress peaks. This reduces friction and heat generation inside the bearing, places less stress on the lubricant, and enables the gearbox to operate more smoothly and with lower losses.

Lubrication is another decisive factor in ensuring long-term bearing reliability. A well-designed oil lubrication system ensures that a protective lubricant film forms between the moving components. This keeps friction and heat generation low and allows the gearbox to generate electricity efficiently over its intended service life.

Practical Example: Modular Planetary Bearing System from NKE FERSA

A practical example of an application-specific solution for wind gearboxes is the modular planetary bearing system developed by Austrian manufacturer NKE FERSA. This system is based on single-row cylindrical roller bearings without an outer ring, RN design, equipped with an inner-ring-guided, one-piece solid brass cage.

The bearings are fitted directly into the planetary gear, the bore of which serves as the mating raceway. This makes efficient use of the available installation space and enables a compact gearbox design. Depending on the load and installation conditions, the single-row bearings can be combined into matched sets of two, three or four bearings. NKE FERSA supplies these bearing sets as ready-to-install matched units. Closely controlled section heights and a coordinated overall design ensure that the radial load is distributed evenly across all individual bearings within the set.

Several elements are combined for use in the planetary gear: retaining rings and flange rings provide axial location, while spacer rings allow the overall width to be adapted to different gearbox sizes and installation conditions. The solid brass cage ensures reliable roller guidance even under high acceleration. Standardized lubrication grooves facilitate lubricant supply. In addition, inspection grooves allow endoscopic inspection of the raceways in the installed condition, supporting condition-based maintenance. The modular planetary bearing system is already used in gearboxes with power ratings of 1.5 MW, 2 MW and 2.5 MW and has proven itself over many years in practical operation.

Operational Reliability and Service Life

In the main gearboxes of wind turbines, the nominal service life of rolling bearings is often estimated at around 20 years. This shows how demanding this application is and how closely bearing design, lubrication strategy and manufacturing quality are linked.

Cylindrical roller bearings optimized for wind power applications, together with a well-designed lubrication supply, suitable surface and cage concepts, and appropriate inspection options, make a significant contribution to reducing failure risk and increasing long-term turbine availability. Ultimately, it is this combination of load-carrying capacity, stiffness, lubricant film reliability and maintenance-friendly design that helps wind turbines deliver their planned energy output over decades.