Wind turbines appear so simple — tall white sentinels cranking gracefully on the horizon. But up close, a wind turbine is an industrial workhorse. Inside the nacelle hundreds of feet off the ground, hot metal gears grind and strain as shifting winds pull and twist the long flexible blades.
At NREL, senior engineers are expanding a research partnership with operators, utilities and turbine manufacturers to determine why some key wind turbine components tend to wear too soon — sometimes within a few years of installation.
That's a problem because wind turbines are expected to operate for 20 years. Early equipment fatigue, especially in turbine gearboxes, threatens to reduce performance and drive up wind power costs just as the industry is poised to capture a greater share of U.S. generating capacity.......Nitty-Gritty of Gearboxes
The tests at the National Wind Technology Center focus on several aspects of gearbox performance.
- Automated spray lubrication. Wind turbines crank at low RPMs under high torque, especially in the first stage of gearing where heat and pressure are high. New designs have lubrication channeled directly to the bearing races.
- Oil cleanliness. New turbines have more aggressive filtration systems.
- Automated gearbox monitoring instruments. These systems are supposed to detect damaging operating conditions before a failure occurs.
- Micro-pitting. This phenomenon occurs as metal fatigue creates microscopic weak spots in gears that degrade the equipment over time.
- Load distributions on the gear tooth contacts and the bearing roller elements.
Initially, the gearboxes under review are being tested on the NWTC dynamometer, where Butterfield and others will simulate a variety of loads and measure the results.
(The image left shows the gearbox of a large commercial wind turbine instrumented for testing at the National Wind Technology Center. Photo credit: Joseph B. Verrengia)
Later, they will put one gearbox into test turbines at the Xcel Energy Ponnequin wind farm and monitor them under real load conditions.
A second testing phase is likely to follow.
Butterfield also intends to build a significant failure database to baseline current failure rates and verify reliability improvements in the future.
"I know we'll discover a tremendous amount in the first year," he said. "We hope we can quickly transfer this experience to the industry."
Learn more about NREL's wind energy research.