Olympic wind turbines rely on SKF bearings

When a leading Chinese wind turbine company, Goldwind, was awarded the contract to supply 33 turbines for the 2008 Beijing Olympic Games, the company selected SKF as the bearing supplier.

The 1.5MW turbines are Goldwind's largest turbines, with machinery at the top of the tower approximately 65m above the ground. This height, plus the fact that wind loadings are greater at increased heights, and larger turbines generate higher powers, meant that the reliability of the bearings was critical.

In choosing SKF, Goldwind based its decision on a good history of co-operation with SKF on smaller turbines, and SKF had already supplied to many larger turbines around the world, including the biggest in the world at that time, REpower's new 5MW turbine that was designed for the extremely tough environment of offshore wind energy generation.

Mrs Qiaozhen Ning, Director of Mechanical Design at Goldwind, comments: "we are very happy to select SKF for this project because we know from experience that they understand the application demands of wind turbines, and the technical support we get from the engineers in SKF China is excellent".

The 1.5MW design is a direct-drive turbine requiring no gearbox, but the turbine mainshaft to which the blades and rotor are connected must be supported by bearings.

Variable loads

One major concern for all turbine builders is the ever-changing wind conditions in terms of continuity, strength, direction and water content (rain). Such conditions mean that the forces transmitted from the wind through to the generator are continually changing. Critical components, like bearings, have to be able to withstand a broad range of forces that are continually changing in magnitude and direction, and also have to be resistant to, or protected from, rain in order to run reliably according to design and application expectations. Such conditions are the main reason why wind turbine applications are considered one of the most demanding for bearings.

Bearings are precision components that are designed for specific ranges of speed, forces, angular misalignment, etc, and their ability to run reliably in such conditions calls for excellent design and manufacturing quality.

While almost all machinery is expected to have some form of 'running attention' and maintenance, unexpected stoppages in wind turbines can be extremely expensive because cranes may have to be hired to dismantle and repair the turbine. And, of course, the turbine is not producing electricity while being repaired. Reliability of critical components is therefore a very high priority for turbine designers, builders and users.

The bearings selected for the 1.5MW turbines are single-row cylindrical roller bearings of almost 1m outside diameter, and a double-row tapered roller bearing of almost 600mm outside diameter. SKF calculations show that both bearings have sufficient capacity and design features to operate reliably in the expected range of weather conditions to be encountered during the Olympic Games, but also for many years after the Games are finished, when the electricity generated will supply 'green' power to the city of Beijing.

Since the contract was awarded to Goldwind, another 10 turbines have been ordered. The 43 turbines now constitute a wind farm on the banks of the Guanting reservoir in Beijing. These turbines show a determination by China to embrace environmental issues and will probably be seen by millions around the world when television reports of the Olympic rowing event, which takes place on the Guanting reservoir, are broadcast in August.