Cristian Soto / Fluitec, Frank Magnotti / Fluitec, Greg Livingstone / Fluitec
Not long ago, wind turbine maintenance was not considered an up-tower activity. Nacelles and their
internal components were not designed for easy access or repair. They required excessive maintenance costs such as crane rentals. Fortunately, new nacelles are designed to be more up-tower friendly with lower operations and maintenance costs. These design refinements reflect the introduction of Breeze 320 from Fluitec, a lubricant condition monitoring company. This oil is designed to be maintained during regularly scheduled maintenance activities. It provides like-new performance for the life of a wind turbine.
Enemies of gear oil failure
Three factors contribute to wind turbine gear oil failure are:
- Oxidation due to thermal stress
- Sludge formation
- Additive depletion
By addressing each failure mode, it is possible to make wind turbine gear oil last three to four times longer than traditional formulations. Similar approaches have succeeded in high-reliability environments such as nuclear power plants. Here’s what each does.
Oxidation, not long ago, was a predominant mode of failure for wind turbine gear oils. Hydrocarbons are much more prone to thermal stress than synthetic oils. With the widespread adoption of synthetic gear oils, it is much less common to see oxidation as the dominant failure mode.
Sludge formation is common in wind turbine gear oils after the fluid is aged and the additives deplete. Sludge can impair flow to critical areas of the system, thereby increasing operating temperatures and wear rates. In the case of planetary gear systems, sludge can cause bearing failures.
Additive depletion. The extreme pressure and anti-wear additives used in gear oils are sacrificial in nature. They deplete over time and cause the fluid to fail. As the additive protection in the gear oil depletes, so does the fluid’s ability to resist against micro-pitting and to carry high loads. It is therefore no surprise that operating a gear oil too long with depleted additive systems will cause gearbox failures. Fluitec has confirmed the relationship between additive depletion and gearbox failure through a data analytics exercise. By analyzing approximately 35,000 turbine-years of in-service gear oil analysis with gearbox failures, a correlation is observed between the degree of extreme pressure, additive depletion, and gearbox failures.
An alternative to oil changes
To combat oxidation, sludge formation, and additive depletion, Breeze 320 uses a synthetic base oil with excellent oxidative resistance, ensuring that under normal operation conditions, thermal stress will not limit the life of the fluid.
The new oil also has high deposit control characteristics that prevent sludge formation. This is accomplished through an advanced additive system that can provide the necessary performance at a fraction of the treat rate compared to some competitive formulations. In addition, the base stock has greater solubility compared to a poly-alpha-olefin (PAO) formulation allowing the oil to “hold on” to depleted additives rather than causing sludge.
And to address the third challenge and ensure that additive depletion is not a failure point in the new oil, an additive concentrate has been developed that allows for up-tower fluid fortification. Each year, an average of 3% of the gear oil reservoir volume is topped off to restore fluid volume to its recommended capacity. Instead of topping off with normal gear oil, users of Breeze 320 top off with an additive concentrate called Boost WT that maintains optimum additive levels.
Operating with a fill-for-life gear oil clearly provides benefits for wind farm operators. The oil offers significant reduction in O&M costs and environmental risk while providing a next-generation formulation that delivers superior gear and bearing protection. The formulation is also compatible with PAO-based formulations on the market. Fluid compatibility is not an issue when upgrading to Breeze 320.
What’s more, the oil is approved for testing by three major gearbox OEMs and currently provides excellent field performance in up-tower maintenance operations. The three most common failure points of wind turbine gear oils are addressed with Breeze 320’s formulation. This synthetic oil provides superior oxidation protection, excellent deposit control, and the additive chemistry formulation can be refortified up-tower for maintenance of optimum additive levels.
Fill-for-life gear oil benefits
Gear oil changes may cost $6,000 or more for an average wind turbine. And it is no surprise that offshore wind turbine oil changes are considerably higher. Eliminating three or four oil changes throughout the life of the wind turbine creates significant savings. Other benefits come from operating with the same gear oil throughout a turbine’s life, such as:
- Continually operating with optimum additive levels. This provides enhanced component protection.
- Oil is like a computer hard-drive in that it stores detailed information on the health of the equipment, contaminant ingression, and condition of the oil. Oil analysis is the tool used to extract this information from the fluid to use in a predictive-maintenance program. Each time the oil is changed, the memory of the “hard-drive” is also wiped clean. There’s significant benefit in being able to contain this critical information to enable better trend analysis and adding to a stronger predictive maintenance program. Standard analysis can fail to reveal correlations to operational failures. Fluitec’s triboanalytics preserve desirable data. And lastly,
- Eliminating oil changes is a more environmentally sustainable practice because each wind farm reduces its waste streams and disposal costs.Transferring oil in and out of the nacelle also has environmental risk, especially if the transfer occurs over water.
Breeze 320 is an important step toward making wind turbine gearbox oil changes a thing of the past, great news for wind farms. WPE
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