A desiccant breather, such as this one from Des-Case, lets a gearbox breath without letting water in.

Oil filters are a relatively simple system and work just as you imagine they do. In simple terms, the oil is forced through a filter media. Particles larger than the openings between the filter fibers get caught and essentially removed from the oil stream.

Of course, there is a whole lot more behind the physics of filtration. “We know that component life is maximized when particles at or around the size of the components sensitive clearances are removed,” says Jay Denslow with Des-Case Corporation. “The challenge is that many of the systems we operate today operate in an environment or industry that demands specific oil filters.”

With an increased attention to gear oil cleanliness and decreasing oil change frequencies, it has become increasingly important to apply lubrication best practices to increase the gearbox life cycle. “Not much has really changed with filters themselves, but the way we filter oil has. Contamination control is the single greatest opportunity for lengthening the life cycle of a wind turbine gearbox. Significant gains can be made with minimal investments due to an inverse relationship between lubrication quality and maintenance costs,” says Denslow.

Wind turbines present a unique set of challenges. Given the importance of production and the penalty of replacement costs, it’s vital that wind turbine gearboxes remain reliable throughout their life. “Gearboxes in wind turbines differ from those in high-speed machinery. In wind turbines, the impact of contaminants on slower turning gear drives is gradual and insidious. Nevertheless, the mean time between failure for gears and shaft-support bearings can be increased by as much as two to three times by maintaining optimum levels of fluid cleanliness and dryness,” says Denslow.

Two major factors―environmental (outside) and operational (location)―contribute to the challenge of maintaining clean and dry oil in wind turbine gearboxes.

Outdoor conditions lead to a surrounding air with particularly high humidity and frequent temperature fluctuations, which contaminates the oil and compromises lubricant quality. “Water contamination can cause corrosion, oil oxidation, additive drop-out, microbial growth, and hydrolysis. A desiccant breather with check valves on the gearbox case almost eliminates the breather’s exposure to the air entering or exiting the equipment – keeping water out while allowing the system to breathe as designed,” adds Denslow.

Remote locations and heights make wind turbines difficult to access and expensive to maintain, making it vital to increase the scheduled time between maintenance, reduce the cost of lubricant replacement, and protect the system from failure. Filtering oil is important, but carrying a filter cart up and into a nacelle is not an ideal way to complete this task. “However, a permanently mounted, continuous-duty offline system for difficult-to-access equipment is recommended. Many inline filters installed in wind turbines only filter down to 10 microns, while an offline filter typically filters down to 3 microns,” he says.

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STAUFF provides a single source for OEM replacement elements.

In addition to its own comprehensive line of hydraulic filters, STAUFF also offers a complete range of replacement elements for most makes and models of filters worldwide. More than 10,000 different STAUFF elements are available online for the interchange market. Users can also get STAUFF quality and reliability even if they do not have STAUFF filters.

While designed for filter housings produced by other companies, STAUFF Filter Elements maintain or surpass the OEM original performance specifications. With STAUFF Filter Elements, users benefit from OEM or better performance. The STAUFF Online Filter Interchange STAUFF maintains an online database for the interchange of replacement filter elements for hydraulic and lubricant applications.

This easy to use interchange is driven by the original filter’s part number. A user simply types in the first four characters from the part number to get the valid STAUFF code for that part number. STAUFF warehouses are stocked with thousands upon thousands of filter elements to provide quick delivery.

STAUFF
www.filterinterchange.com

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RSC’s XEnviroLogic 132 is a biodegradable oil that offers safety and performance benefits when used in the hydraulic pitch control mechanisms of wind turbines.

By one estimate, 80% of all breakdowns in lubricated machines are related to pollutants in the oil. Even in small amounts, contaminants can increase operating costs associated with maintenance, downtime, or equipment replacements. Enough particles measuring only 1-μm in size (invisible to the human eye) can knock out a 20-ton gearbox.

The solution: rigorous particle contamination control. Ideally, this process should begin well before a gearbox is ever placed into service. The interior gear housings should be painted with an epoxy sealer to provide a smooth surface that’s easy to clean and that seals in debris, such as casting sand. Prior to assembly, all components should also be properly stored in a clean, dry area.

Common sense says that a better filter can lengthen equipment life and research bears this out. For instance, upgrading the filtration system of a gearbox can significantly increase gear and bearing life (some have reported by up to six times or more). What’s more, gearboxes are often equipped with inadequate filtration systems.

In a 2014 article, oil filtration experts C.C. Jensen pointed to a possible industry misunderstanding that inline filters are enough to keep gear oil clean. They site findings that show the addition of offline filters can extend component life by at least 50%, doubling gear oil life. An offline filter uses a low-flow pump to continually circulate and purify oil. Although like many things in life, it’s most effective when used with consistency.

Filters are an important line of defense against contamination, but the type of oil used is also significant. It has been referred to as the “lifeblood” of a turbine, affecting everything from the bearings to the generator. Most gearboxes failures are preventable and are a direct result of improper lubrication and lack of routine maintenance.

Lubricants vary per component and are usually designated by the manufacturer. An important choice for a turbine owner, however, may be whether the oil is synthetic or mineral-based. Though often more costly, years of research has continued to demonstrate that synthetic oils offer better viscosity-temperature characteristics and provide better wear protection.

This is important when considering the ambient weather conditions lubricants must perform in. For example, freezing temperatures can cause high-lubricant viscosity, leading to filter failures and, ultimately, turbine shutdowns. Conversely, a strong, continuous output can generate high gear-oil temperatures, which at extremes can also lead to equipment breakdowns.

Finding balance is imperative to successful turbine operation and, today more than ever before, lubricants are available that optimize a variety of traits in one product. One of the latest gearbox lubricants on the market is formulated to provide component protection over long oil-drain intervals, and offers an industry-first, seven-year warranty. Considering the fact gearboxes are lucky to make it to five years, a lubricant guaranteed to work past that time holds an enormous cost-saving potential. Another plus: extending oil-drain intervals means reducing oil maintenance and the associated maintenance costs in remote, often harsh conditions.

Recently, interest in non-toxic, biodegradable lubricants has been growing, which seems only fitting. It’s been estimated that most early turbines, including up to 90% of those in Europe, use mineral oil, which is non-renewable and non-biodegradable. This is changing with the latest synthetic lubricants hitting the wind market that provide bio-based solutions. Most still promise long-lasting anti-wear and corrosion-resistance, often with an additive package.

Along with environmental concerns and risk of leakage (a single turbine may contain some 200 gallons of oil), a benefit of synthetic lubricants not often discussed relates to safety. For instance, lightning strikes or electrical malfunctions have the potential to ignite oil in a turbine, a potential that elevates with standard, mineral-based products. Synthetic lubricants, however, often offer a higher flash point with lower volatility, providing a worthwhile safety margin.WPE

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