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First Full-Scale Evaluation of Gearbox Failure Generates Industry Interest

November 21, 2017

Although the cost of wind energy has declined dramatically over the past two decades, operation and maintenance costs are often higher than anticipated at an average of half the power purchase agreement price. One of the primary drivers behind these costs are wind turbine gearboxes, which often require repair or replacement well before reaching their design life.

A new article in the journal Wind Energy by National Renewable Energy Laboratory (NREL) researchers Yi Guo and Jon Keller, "Investigation of high-speed shaft bearing loads in wind turbine gearboxes through dynamometer testing," summarizes the first full-scale assessment of operating conditions that may generate white etching cracks (WECs) in the bearings of wind turbine gearboxes—one of the most common causes of failure.

Guo and Keller assessed the behavior of the 750-kilowatt (kW) gearbox bearings through modeling and testing in the 2.5-megawatt (MW) dynamometer. By introducing transient braking and grid-loss conditions, the team found evidence of high stresses alternating with low loads, torque reversals, and roller sliding—all of which can promote axial cracks in the bearings.

"Focusing on these dynamic torque events during the design and operational phases can be crucial to alleviate WEC formation and the resulting damage," says Guo.

The publication of Guo and Keller's journal article has generated industry interest from SKF GmbH and the Winergy Drive Systems Corporation in participating in the next phase of the research. For this campaign, an instrumented Winergy gearbox with SKF bearings will be installed in the General Electric 1.5-MW SLE turbine at the National Wind Technology Center this month. A wide range of operating conditions will be evaluated during the 1-year validation campaign.

Results will be critical in further assessing the contribution of conditions such as roller sliding, which will be directly measured inside the wind turbine, in addition to loads in the development of WECs in wind turbine gearboxes.