Cost-effective wind turbines need reliable components. As one of the world’s leading rolling bearing manufacturers and development partners to the wind turbine industry, Schaeffler has been producing bearings for wind turbines for over 30 years. With its extensive expertise, the company offers the right bearing solution for every wind turbine and a comprehensive concept to further increase the reliability of wind turbines.

Rolling bearings play a key role in functioning wind turbines. With onshore and offshore wind power, demand for reliable components has increased greatly in recent years. The growth of the systems to multimegawatt power plants leads to higher forces and torques, which put more strain on components. At the same time, downtimes and maintenance work on offshore systems produce higher costs.

The global expansion of wind energy is not slowing down. Stronger systems, versatile system concepts and short innovation cycles require new solutions for rotor bearings. To develop those bearings with the necessary robustness and reliability in the shortest possible time, Schaeffler combines simulations and calculations with measurements from its large-bearing test rig Astraios, which began operating five years ago.

Important data

"Over the past few years, we have validated the results from the simulation and calculation of wind turbine bearings on the test rig," says Andreas Mangold, manager of strategic engineering at Schaeffler. "As a result, we have been able to significantly reduce the risk of possible failures first occurring in the field."

Schaeffler, which generated sales of approximately €13.2 billion in 2015 and has about 84,000 employees working in approximately 170 locations in over 50 countries, is one of the world’s largest family-run companies. It tests rotor bearings for wind turbines of the multimegawatt class on the Astraios large-bearing test rig. These bearings have an outside diameter of up to 3.5m.

As one of the largest state-of-the-art test rigs in the world, Astraios is able to apply changing load conditions created by wind, weight and dynamics from real operations to the test bearings at various speeds.

In comprehensive test runs with a variety of concepts for rotor bearings, engineers have obtained extensive data on the behavior of large bearings, which can differ significantly from small rolling bearings.

Optimise simulation models

Schaeffler uses the data in a variety of ways. "On the one hand, we are able to ensure that the newly developed bearing solutions leave the production hall robust and reliable," Mangold says. "On the other hand, we validate and optimise the simulation models with the data. We test in practice and use the results for the further development of our simulation tools."

Although the calculations for the operating life of smaller rolling bearings can be applied to large bearings, this does not apply to other parameters such as kinetics or friction torque.

Therefore, simulations in these areas must be validated based on test results. The measurements obtained with Astraios are used by the developers of the simulation models to adjust and refine their calculations for the respective bearing types. Based on previous knowledge gathered in this way, engineers at Schaeffler are able to develop new bearing concepts for wind turbines in a very short time and design them optimally to meet any requirements. Using the verified simulation models, the engineers are also able to validate results from the currently tested diameter of a large bearing to even larger bearings and whole platforms.

Simulation of complete wind turbines

Schaeffler is able to develop integrated solutions for new wind turbine requirements, such as different bearing types. For an application-oriented test, it is important to correctly define the parameters so that loads and deformations agree with the operating situation in the field. Using the SIMPLA software for multibody simulation, developed by Schaeffler, the engineers are able to map a complete wind turbine, and examine it from the wind field down to the rolling contacts.

As a result, they are able to discover the correct parameters for validation on the test rig. The measurements are incorporated in the simulation models in a multistep process, which then calculates the loads and kinematic behaviour of a large bearing.

If, for example, deformations are found, the effects on the function of the rolling bearing can be calculated and validated on the test rig.

A practical result from this could be the adjustment in the design or coating of a bearing, but also recommendations for the lubrication of various operating conditions. This can be a great advantage in offshore wind turbines, because maintenance work at sea is usually very expensive and complicated.