Piezo sensor predicts wind farm failure

Engineers have developed a piezoelectric sensor that lets wind farm operators know when bearings are about to fail, a development that could prevent costly downtime.

The sensor, developed by Wenqu Chen, a mechanical engineering research student at Sheffield University, uses ultrasonic waves to measure the load transmitted through a bearing in a wind turbine. A paper describing the advance is published in Proceedings of the Royal Society A.

Prof Rob Dwyer-Joyce, co-author of the paper and director of the Leonardo Centre for Tribology at the University told The Engineer that a limiting factor with wind turbines is gearbox reliability, particularly in relation to bearings where manufacturers and operators have faced issues with reliability.

He said: “[Failures] come from the fact that these are big bearings subject to quite unusual loading.

“They’re subject to high dynamic loading and they’re failing in ways that aren’t usually seen on more conventional bearings seen in trucks and cars and process machinery.”

The 2mm2 sensor has been validated in the lab and is currently being tested at the Barnesmore wind farm in Donegal, Ireland by Ricardo.

Prof Dwyer-Joyce said the patented sensor has been installed in the raceway of a transmission bearing, adding that the raceway compresses slightly as the ball and roller pass over it.

“We pick up that compression and that compression depends on the load applied to the ball in the first place,” he said. “It’s that stress…which is going to control the life of the bearing.”

The time of flight of the ultrasonic pulse from the sensor is affected by the stress level in the material, making the new method the first to directly measure the transmitted load through the rolling bearing components.

Current sector-related condition monitoring methods come in the form of acoustic emission signal, vibration sensing, or oil debris analysis that alert operators to damage after it has occurred, which puts the new sensor – and its size – at an advantage.

“Imagine the rolling elements,” said Prof Dwyer-Joyce. “The balls and the rollers passing underneath the raceway – if you’ve got a very small sensor…the contact between the roller and the ball and the raceway is really very small so you get a very localised stress region…the smaller your sensor then the more its sensing path is within that stress region.”

Prof Dwyer-Joyce added that discussions have taken place with bearing manufacturers regarding the installation of the sensor at the point of manufacture.