Product category:
Bearings
News Release from: Schaeffler (UK) | Subject: SL18 18 and SL18 29
Edited by the Engineeringtalk Editorial
Team on 12 March 2002
Bearings fit for wind turbine duties
Thanks to the isolation of most wind turbines, their gearbox bearings must be highly reliable.
Wind power is being seen as an increasingly attractive source of energy and there is growing demand for individual wind turbines and for wind farms consisting of many turbines Most of these installations are in isolated locations - some even at sea - and this, coupled with tall support towers and a requirement for a long operating life, means that the gearbox bearings must be highly reliable
In addition to providing high reliability, such components must also take high loads (which are not constant), be highly efficient, make little noise and require minimal space.
To meet these needs, the three key factors behind a successful gearbox bearing are the calculations, design and selection.
A typical wind turbine gearbox will have a single-stage planetary gear and a secondary two-stage spur gear to raise the speed sufficiently to operate the generator.
Throughout the gearbox therefore, from the planet carrier/spider to the final output stage, the bearing performance criteria will be different.
At some points the requirement is to carry medium-sized loads at low speeds, while elsewhere the bearings need to carry much lower loads but at far higher speeds.
In addition, some of the bearings will be subjected only to radial loads, while others may need to resist axial thrusts.
Ina's SL18 18 and SL18 29 full complement cylindrical roller bearings are best suited to the requirements of the planet carrier, which must support medium-sized loads at low speeds.
The low speeds mean that precision versions with reduced radial clearance can be specified, thereby helping to improve the performance, accuracy and life of the entire planetary gear assembly.
Looking at the output shaft, where high speeds and low radial loads are found, the requirement is very different.
LSL 19 23 cage-guided cylindrical bearings would be one possible solution, or self-aligning bearings could be used.
Another alternative would be to employ four-point contact ball bearings that could act as double-direction thrust bearings.
This last option would require the bearing to be mounted with increased bearing clearance and loose radial location.
Elsewhere in the gearbox, Ina would recommend single and double-row full complement roller bearings, cage-guided roller bearings, cylindrical roller bearings without an outer ring, and matched pairs where two bearings need to be mounted close to each other for load-sharing.
Every application within the gearbox will have different requirements and, as such, must be considered individually.
However, the calculations need to take the overall system into account.
Ina's application engineers have extensive experience of bearing calculations, design and selection, as well as ample relevant experience with wind turbine gearbox applications.
Customers are encouraged to make full use of this so as to develop fully optimised gearbox designs as cost-effectively as possible.
Ina offers specifiers two alternatives for preliminary bearing selection: an online system and the medias professional CD-ROM.
Furthermore, the Ina Bearinx calculation program allows the user, with the assistance of the Ina engineering service, to model the entire power flow through the wind turbine.
Only by considering the overall system - and taking account of the influence that each component has on the others - can an optimised solution be found.
The sophisticated software also allows the user to investigate the impact of other unusual phenomena that can be encountered in wind turbines, such as the low-load and low-speed conditions that arise when winds are light, possibly leading to the breakdown of the hydrodynamic lubricating film that is normally required for a long bearing life.
An illustrated technical paper (WWG) is available from INA, entitled "Rolling bearings in wind turbine gearboxes".
This contains a substantial amount of information on the particular requirements of wind turbine gearboxes and the correct design of rolling bearings to meet those needs. Request a free brochure from Schaeffler (UK) ...
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