London, Aug 15 (IANS): The efficiency of wind turbines can be increased and repair costs reduced through a new technique developed by engineers from the University of Sheffield.

The novel technique can predict when bearings inside wind turbines fail which could make wind energy cheaper.

Unexpected bearing failures are a common problem in wind turbines.

"By removing the risk of a loss of production and the need for unplanned maintenance, it can help to reduce the cost of wind energy and make it much more economically competitive," said co-author of the paper professor Rob Dwyer-Joyce.

The method, developed by mechanical engineering research student Wenqu Chen, uses ultrasonic waves to measure the load transmitted through a ball bearing in a wind turbine.

The stress on wind turbine is recorded and then engineers can forecast its remaining service life.

When a bearing is subjected to a load, its thickness is reduced by a very small amount due to elastic deformation, and the speed of sound is affected by the stress level in the material. Both these effects change the time of flight of an ultrasound wave through a bearing.

The new method is the only way to directly measure the transmitted load through the rolling bearing components.

It uses a custom-built piezoelectric sensor mounted in the bearing to measure the time of flight and determine the load.

This sensor is less expensive and significantly smaller than currently available, making it suitable for smaller turbines.

It can also provide a better prediction of the maintenance needed, saving money in servicing, researchers said.

The study was published in the journal Proceedings of the Royal Society.