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NREL - National Renewable Energy Laboratory
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Gearbox Reliability Collaborative Projects

Gearbox deficiencies are the result of many factors. Through gearbox modeling and testing, condition monitoring, and the failure database, the collaborative is expanding the industry's knowledge base, recommending efficient and cost-effective improvements, and facilitating immediate improvements in the gearbox life cycle.

Gearbox Modeling and Testing

Illustration of representative gearbox including the hub, main bearing, main shaft, gearbox, brake, high speed shaft, generator, and bed plate.

A complete gearbox redesign has been completed in a collaborative effort between NREL and industry partners. This process documented and analyzed the design process and produced a new gearbox design that integrates knowledge from previous Gearbox Reliability Collaborative (GRC) activities. The new design represents the next phase in the GRC project, and will be compared with the results of the GRC's baseline testing and modeling. The goal of gearbox testing is to build an understanding of how wind turbine loading conditions, including both steady state and transient events, translate into gear and bearing response. The tests examine gearbox reactions, load distribution, displacements, temperature, stresses, and slip.

The test data from the representative gearboxes are used to evaluate gearbox modeling tools and to assess a comprehensive matrix of design loads required for wind turbine gearbox design and testing standards. While wind turbine gearboxes commonly meet and exceed design criteria specified in current industry standards and third party certification criteria, a gap exists between estimated and actual gearbox reliability. The GRC addresses this gap, examining critical design process elements and exploring whether there are insufficiencies in modeling tools. Rectifying gaps in design and modeling processes will result in increased gearbox reliability and an overall reduction in the cost of wind energy. Collaborative members have initial access to non-proprietary models and test data.

Condition Monitoring

Gearbox condition monitoring techniques are examined during testing. Condition monitoring is a method to assess a system's health, enabling proactive maintenance planning, reducing downtime, reducing operations and maintenance costs and, to some extent, increasing safety. Techniques such as vibration, acoustic emission, electrical signature, oil cleanliness, oil debris, and oil sample analysis are evaluated through faults that naturally occur during the testing. Collaborative members have initial access to non-proprietary data from the condition monitoring tests.

Failure Database

A robust, well-populated failure database of gear and bearing condition information gathered during gearbox tests, inspections, rebuilds and overhauls provides a summary of gearbox component faults to document root cause analyses in a tool that identifies key failure trends. Once identified, the trends allow researchers to focus on the solution to gearbox challenges and the database provides a method to measure improvements. Collaborative members have initial access to non-proprietary, summary information and statistics from the failure database.