Single bearing designs improve the efficiency and reliability of multi-megawatt wind turbines

The Schaeffler Group has developed a single bearing design concept for multi-megawatt wind turbine rotor shafts, which not only improves the energy efficiency and reliability of the turbine, but also eliminates drive train components, helping to reduce the overall weight of the turbine.

By using its in-house advanced rolling bearing calculation software BEARINX^Ò, in combination with Finite Element Analysis tools and multi-body simulation (MBS) models, Schaeffler's engineers can assist customers during the initial stages of wind turbine design. This helps to improve the reliability and efficiency of the turbine under a wide variety of load conditions. Schaeffler is able to develop bearing designs that are tailored to specific wind turbine requirements, including turbines for both onshore and offshore wind farms.

This powerful combination of software enables Schaeffler to evaluate various load conditions and to accurately assess all relevant, critical load conditions for wind turbines. The use of 'moment' bearings in single bearing designs enables a high level of system integration, resulting in extremely compact, less complex wind turbine designs. The preloaded bearing also prevents the transfer of negative axial loads to the wind turbine drive train.

Trend towards single bearing designs
The trend towards large, multi-megawatt wind turbines, particularly in offshore wind farms, has led to a change in the design of bearings for wind turbines. Single bearing designs are becoming increasingly important.

With single bearings, the wind turbine rotor is supported only by a single, double row tapered roller bearing or 'moment' bearing, typically in a back-to-back arrangement that supports all forces and moments. This concept can take many different forms, for example, with a shaft and gearbox and a high-speed generator, as a hybrid solution with shortened gearbox and medium-speed generator, or as a direct drive without a gearbox.

Single bearings always result in more compact designs. For example, the wind turbine nacelle can be fully integrated with the bearing-gearbox-generator unit. This means that it is possible to eliminate drive train components and reduce weight. This in turn reduces the head weight of the wind turbine, allowing smaller foundations to be used and simplifying logistics.

Another advantage of the single bearing design is that preloaded tapered roller bearings can be utilised, which prevent axial clearance and small axial misalignments. This controlled guidance of the rotor shaft means that fewer movements act on the system, reducing the negative effects on the gearbox and generator.

Evaluation of all load conditions
Schaeffler has already implemented numerous single bearing solutions for customers, including 5MW offshore wind turbines. To engineer bearing variants for applications such as these is particularly challenging, as standard software tools cannot be used for the design and calculation of the bearing rating life. Schaeffler has therefore expanded BEARINX^Ò to include elasticity effects, which are calculated using Finite Element Methods (FEM). BEARINX^Ò can now analyse bearings including the influences of housings. Around 250 classified load cases are evaluated taking all elasticities into account, resulting in an optimal design that considers almost every conceivable critical load condition.

The results of the FEM calculations for the housing are transferred to a 'rigidity matrix' and entered into the BEARINX^Ò calculation. This matrix represents not only the elasticities at individual bearing positions, but also the influences of the elasticities from one bearing position to another. BEARINX^Ò is therefore able to perform complete rating life calculations based on the load distribution and elasticities. This means Schaeffler has a unique calculation tool for designing rotor bearings for multi-megawatt turbines.

Schaeffler supplies moment bearings that are individually designed to match the respective turbine. These bearings are supplied with classic steel pin cages or with plastic (PEEK) segmented cages. PEEK is a lightweight, high-strength plastic with low wear characteristics, which is also able to support high forces. The plastic segmented cage reduces friction and increases the efficiency of the turbine. This cage also improves the guidance of the rolling elements, whilst optimising lubricant supply. Moment bearings can also be supplied with integrated anti-corrosion protection, which is achieved by applying a zinc flame-sprayed surface coating and multi-layer painting. Special hardening processes enable custom material characteristics for integrated functions such as seals or connections to adjacent structures.

For further information, e-mail: info.uk@schaeffler .com or view website: www.schaeffler.co.uk   Refer to page 7

System know-how and solutions for all bearing positions on wind turbines

The Schaeffler Group's Wind Power Business Unit has more than 30 years' experience in the development and manufacture of rolling bearings for wind turbines and is an important development partner for all manufacturers of wind turbines and wind turbine gearboxes worldwide.

Schaeffler's bearing range comprises much more than innovative rolling bearing solutions. The range also covers the entire process chain, from bearing development and prototyping through to volume production. Customers are supported with Schaeffler's in-house bearing calculation and simulation software for wind turbine design and specialist engineers for rolling bearing mounting and tribology. Product and engineering know-how, technical consultation and a close working partnership with the customer help to reduce development times and to increase quality, reliability and cost-effectiveness of bearing solutions.

Local support, production and service on a global basis
As well as bearing development and application engineering, Schaeffler also provides highly qualified, specialist external sales engineers who can provide comprehensive advice to customers, on site if necessary. Schaeffler's manufacturing plants for wind energy bearings are close to customers too, with bearing plants located in Germany, Romania, China, India and North America.

Schaeffler is the only manufacturer worldwide with solutions for every bearing position on a wind turbine: rotor shaft, gearbox and generator, as well as for wind tracking and blade adjustment.

Today, at least one Schaeffler component is installed on around 50% of the total number of wind turbines installed globally. Manufacturers therefore rely on Schaeffler's technical know-how when it comes to the design, development and optimisation of wind turbines and their components. Detailed attention is paid to all customer requirements as early as the project planning phase, which means Schaeffler is able to contribute towards minimising wind turbine operating costs.

High performance bearing concepts for rotor shafts
Rolling bearings for wind turbine rotor shafts are subjected to high dynamic loads and operating conditions. Schaeffler develops rotor bearings for the latest wind turbine variants, from 220kW up to multi-Megawatt class turbines. These different turbine concepts range from the conventional, 3-point shaft bearing arrangement and hub bearing supports, through to 2-point shaft bearings or single bearing concepts.

Bearing housing designs are calculated using Schaeffler's bearing design and calculation software, BEARINX, and FEA analysis software, which together ensure optimal support of forces and moments.

Examples of recent innovations from Schaeffler include bearing solutions that combine tapered roller with cylindrical roller bearings, which provide angular adjustment, enabling very tight axial guidance of the rotor shaft. Another innovation is the X-life radial spherical roller bearing, which can now be supplied in standard bearing sizes with a sheet steel cage rather than the conventional solid brass cage.

The right bearing for every gearbox
Bearings for wind turbine gearboxes face the challenges of high dynamic forces with extreme peak and minimum loads, sudden alternating loads, as well as fluctuating operating temperatures.

Schaeffler therefore supplies bearings with high static safety ratings and reliable dynamic designs. Current examples include the Tube Roller Bearing with tube rollers that enable the bearing to rotate without slippage under all load conditions. A high capacity bearing is also available that enables high load ratings and lower friction due to newly developed cage geometry.

Wind tracking and blade adjustment
Wind turbines must be correctly aligned to wind conditions. The tower and the rotor blades need to be adjusted so that they make optimum use of present wind conditions and are not subjected to excessive loads that could cause damage.

Tower and blade adjustment are therefore critical for the cost effective operation of wind turbines. To solve these issues, Schaeffler has developed and manufactured slewing rings with outside diameters up to 4,000mm. These bearings are ideal for wind tracking of the nacelle and for adjustment of the rotor blades in wind turbines up to 5MW output.

Condition monitoring
Schaeffler Industrial Aftermarket Division offers a wide range of solutions for the condition monitoring of wind turbines. Installing a condition monitoring system improves the planning of maintenance intervals and prevents any unplanned downtime, which reduces costs significantly for wind turbine operators.

Schaeffler's FAG WiPro s is a new compact online condition monitoring system for carrying out reliable, continuous vibration monitoring of wind turbines. The system continually monitors vibration to avoid costly unplanned shutdowns. These include damage to bearings and gears, as well as shaft misalignments. If a specified threshold value or alarm limit is exceeded, the system triggers an alarm. The vibration monitoring data can be analysed directly on site at the central control station or can be retrieved via a TCP/IP link and analysed by either the end user or by Schaeffler Industrial Aftermarket. This means that operators can make changes to system parameters remotely from anywhere in the world.

In addition, Schaeffler's oil monitoring system, the FAG Wear Debris Monitor, is an additional sensor that enables the early detection of damage to heavy duty, oil-lubricated industrial gears. The system enables damage in gearboxes to be detected at an early stage and the cause determined precisely, providing plant operators with a reliable system that prevents unplanned downtime and minimises maintenance, repair and overhaul (MRO) costs.

The Schaeffler Group in profile
The Schaeffler Group with its product brands INA, LuK and FAG is a leading manufacturer of rolling bearings and linear products as well as a renowned supplier to the automotive industry of high-precision products and systems for engines, transmissions and chassis applications. The group of companies stands for exceptional customer focus, innovative ability and the highest possible level of quality. Sales of over 9.5 billion euros were generated at over 180 locations in more than 50 countries in 2010. With around 70,000 employees worldwide, the Schaeffler Group is one of the largest German and European industrial companies in family ownership.

For further information, e-mail: info.uk@schaeffler .com or view website: www.schaeffler.co.uk   Refer to page 7