By Brian Burks, CLS, OMA 1
Senior Application Sales Engineer
The wind industry is changing and growing quickly. There are now more than 89,077 MW of wind energy installed across 41 states. To keep up with clean-energy demands, wind turbines have had to become more powerful and reliable. This means wind turbines are expected to run more efficiently and for longer periods with less maintenance — and that means every component must operate flawlessly.
Turbine lubricants play a critical role in reliable equipment operations and maintenance. It can help protect system components, minimize unscheduled downtime, extend maintenance intervals, reduce costs, and enhance safety (thanks to fewer trips up-tower). There are a number of lubrication points in a wind turbine, including generator bearings, pitch and yaw systems, and — perhaps most essential — the gearbox. A well-lubricated gearbox is critical to reliable turbine operation and production.
Just a few years ago, oil changes were done every three to five years in gearboxes because of lackluster performance that degraded quickly over time. Lubricant performance was typically fraught with contaminants such as water, foam, or the accumulation of excess sludge that required frequent maintenance checks. However, it is extremely costly and labor intensive to change the oil on every single turbine at a wind site every few years. In fact, it has proven unnecessary when using high-quality, balanced lubricant formulation. The key is choosing a properly formulated lubricant for each turbine.
With so many lubricants available today, how can you know if you’ve chosen a quality product? Here are the top five indicators of a quality gearbox lubricant.
1. Look for anti-foam properties
One of the best indicators of a high-quality lubricant is one with excellent anti-foam properties. When gear oil encounters challenges such as air entrainment, incompatible oil mixing, or water, excessive foaming can result. Too much foam may lead to premature wear and gearbox failure.
Wind operators can expect a small amount of air entrainment during gearbox operation. However, when a turbine is shutdown for maintenance, the accumulation of entrained air or foam should dissipate after about 15 minutes. This means that by the time a wind technician has safely climbed up-tower for an inspection, the gearbox should be foam-free.
If it fails to pass the foam-free test, consider switching lubricants during the next scheduled oil change.
2. Choose solids-free additives
Look for gear oil that is blended with a balanced formulation. This means that if additives are included in the formula to resist water, foaming, and wear, this formula must remain balanced. For example, many lubricants leverage a silicone-based additive to prevent foaming. However, because of its attraction to an oil water interface, silicone particles are more likely to be caught in the filter.
Certain additives may be filtered out, but this can also subject gearboxes to foaming, micropitting, sludge buildup, or scuffing wear. Micropitting is a common challenge for wind operators, which can form on surface-hardened gears within the first several hours of operation if the gearbox is not properly lubricated.
A better option is a solids-free lubricant, which has proven to stand up to years of use and ultrafine filtration without depleting important additives or requiring costly top-treating procedures. Additive top treating gearbox oil is one way wind maintenance teams have tried to mitigate lubricant degradation and extend oil life. The concern with top treating is it may introduce new contaminants or affect the formulation of a balanced oil, which could impact gearbox performance.
Choosing solids-free lubricant from the factory fill is the best way to extend the lifespan of gearboxes and maximize turbine production and profits.
3. Consider water resistance
Water is a critical contaminant in a wind-turbine gearbox. Even small amounts can shorten gear, bearing, and oil life. Excess water in a gearbox can result in water attaching to additives, and clogging up the filter. This may lead to insufficient additive levels in the oil and can aggravate or increase lubricant foaming, ultimately leading to poor performance or turbine downtime.
The wind industry typically use the Cantley formula, which posits that when oil contains 100 parts per million (ppm) water, users can expect to get 100% bearing fatigue life. If oil absorbs higher amounts of water, research shows that bearing life is shortened, which negatively impacts energy production and gearbox lifespan.
4. Remember the filter
Many turbines are equipped with very fine filterability capabilities, which are essential for overall gearbox health. Oil filters require changing about every six to 12 months when using a quality lubricant. Lower-quality lubricants may clog filters faster, requiring new filters every three months or so and may reduce the lifespan of a turbine. This is a costly task and an inefficient maintenance program.
Filter media size should play a role in lubricant choice. Most OEM industry standard filter media is 10 microns, but many oils fail to perform optimally with this filter size. For example, some additives, such as silicone anti-foam, may become stuck in the filter and be removed from the lubricant. Silicone’s attraction to oil water interface can lead to accelerated filtration removal of silicone additives.
For improved performance and equipment lifespan, choose a lubricant that recommends 5-to- 10-micron filters for full-flow inline applications, and 3-micron filters for fine offline filtration. An oil that can handle finer filtration without compromising its quality or lifespan is ideal and will provide lower contamination levels and increased performance.
5. Buy American
When a lubricant is certified, “Made in the United States,” it typically ensures the product offers quality ingredients without mysterious additives or fillers that can clog filters, slow turbine performance, or impact production. Buying local also supports the wind industry in America.
When you invest in quality lubricants, you’ll generally see superior performance for the entire lifespan of your infrastructure while cutting operational costs. That sounds like a win-win.