Page 39 - North American Clean Energy September/October 2019 Issue

Figure 3: Cutaway view of the FZG test rig showing the sample gearset arrangement.
sulfur compounds that adsorb onto tooth surfaces to form a protective layer over asperities. This boundary layer prevents the asperities from welding to one another, protecting the gear teeth from scuffing, as shown in Figure 2.
One standard method for evaluating the effectiveness of the extreme pressure additives in a gear oil is the FZG scuffing test. FZG stands for the "Forschungsstelle fur Zahnrader und Getriebebau", which is the German name for the Institute of Machine Elements at the Technical University of Munich, where the test method
was developed. In this test, a standard sample gearset is lubricated with the gear oil, as shown in Figure 3. The gearset is then subjected to increasingly severe operating conditions in a series of stages. After each stage, the gearset is inspected; if the damage and wear are within acceptable limits, the next stage of the test is initiated with more severe operating conditions. The FZG fail stage for a gear oil corresponds to the stage in which the wear exceeded the acceptable limits.
There are several variations on the FZG test, so care must be taken to ensure the same test conditions were used when comparing gear oil datasheets against one another. FZG test descriptions
and standards will be noted on the datasheets, along with a series of letters and numbers separated by “/” marks denoting the operating conditions. Most wind turbine gear oils will surpass the passing criteria of the final stage in the commonly used FZG A/16.6/90 scuffing test. Therefore, more severe tests, such as the FZG A10/16.6R/90 scuffing test, are required to differentiate wind turbine gear oil performance.
Side-by-side field test data can provide additional insight into wear
and scuffing protection. A typical field trial involves selecting several similar turbines at a single wind farm and filling them with different gear oils. Over the course of several years, the turbine gearboxes are monitored (using oil sampling, instrumentation, and maintenance records) to determine the best performing oil. This approach has been employed by O&M companies seeking to maximize turbine availability.
Other Considerations
While the primary purpose of a gear oil is to protect gear teeth, a good gear oil must also lubricate bearings, endure years of service, and protect against corrosion. Wind turbine operators seeking to maximize uptime should consider gear oils from several manufacturers
to determine which product best meets their needs. Any differences in the initial product cost may easily be outweighed by the extended service intervals and better gearbox reliability offered by higher quality gear oils.
Austin Guenther, P.E. is the Chief Marketing Officer of Hydrotex, a manufacturer and distributor of wind turbine gear oils, hydraulic fluids, and greases. He has a Bachelor of Science in Mechanical Engineering from Marquette University, and a Masters of Business Administration from Georgia Tech.
Eli Lester is the Wind Power Market Segment Leader for Hydrotex. He has over a decade of experience in the lubrication industry and has trained technicians from several O&M companies on wind turbine lubrication best practices.
Hydrotex /// www.hydrotexlube.com
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