Going Green - Wind Turbines & Lubricant Testing
Wind energy
continues to grow in importance in the US and around the world. With
about 380 billion kilowatt-hours produced in the US in 2021, it accounted
for about 9.2% of electricity generated nationally, according to the US
Energy Information Administration (EIA). Wind generation made up
almost 7% of all electricity generated around the world in 2020 with US
wind generation accounting for about 19% of the total. The EIA
predicts continued growth in wind energy over the next 30 years, and this
ongoing growth is visible in Savant Labs' neighborhood. In
2020, Michigan power company Consumer’s Energy brought 150 megawatt of
wind generation online in Gratiot County, just a few miles south of
Savant’s location in Midland, Michigan, and another 200-megawatt project
is underway there this year.
Serving the
Lubricant Industry
To best serve the lubricants industry, Savant Labs are providing wind
turbine lubricant testing to support wind generation locally, nationally,
and internationally. With the high forces, high rotational speeds,
and variable conditions a wind turbine experiences in operation,
lubrication is critical. Figure 1 shows many of the moving parts
that require lubrication in a typical wind turbine.
Wear of
Key ComponentsThe gearbox is generally considered the most important and
vulnerable lubricated component. The US National Renewable Energy
Laboratory (NREL) completed a study in 2011 that showed that gearbox
damage was the leading cause of downtime and the most expensive repair
for the wind turbines in use (Sheng et. al., 2011). The gears are
susceptible to surface wear such as micro-pitting and
scuffing. Lubricants with antiwear and extreme pressure additives
can protect against scuffing and other surface wear. Furthermore,
the use of the fluid with the proper viscosity provides an adequate film
thickness to prevent contact between the gear teeth. Micropitting can
also be exacerbated as an oil oxidizes in service and contains higher
levels of acidic compounds.
Along with gearbox damage, damage to the main shaft and bearings or the
generator account for the majority of all downtime. Excellent antiwear
properties and proper viscosity across the operating temperature range
are typical requirements to maintain proper bearing function, for both
oils and greases used in wind turbine bearing applications. Furthermore,
there is some implication that certain additives may encourage hydrogen
absorption in the bearings, contributing to the much-researched but still
poorly understood phenomenon of white etching cracks (Aikin, 2020). These
cracks are a major concern because they can lead to very premature
bearing failures.
Materials
Compatibility
In addition to these specific wear problems, wind turbine fluids must
exhibit good materials compatibility. For instance, they must not
damage seals, which can cause fluid leakage. Compatibility with paints
and coatings used in the wind turbine is also important. As with all
lubricants, wind turbine fluids need to resist foaming, minimize
corrosion, and exhibit good oxidation stability, which extends the drain
interval. Finally, the lubricant needs to have good pumpability across
the operating temperature range, which can include cold ambient
temperatures in higher latitudes. Many of the same tests that are used to
validate automotive oils or industrial gear oils can be used to evaluate
whether a lubricant is well suited to a wind turbine application. Some
possible tests Savant Labs offer and what they tell about a fluid
are listed in Table 1.
In-Service Fluid
Monitoring
In addition to determining whether fluids are generally appropriate for
wind turbine applications, the wind generation industry makes extensive
use of in-service fluid monitoring. Many installations use in-line
sensors to monitor overall cleanliness or conductivity, which can
indicate some level of information about wear and oil degradation. Even
more important, the standard practice in the industry is to sample the
gearbox oil about every six months during scheduled maintenance and send
it to a testing lab, such as Savant Labs, for analysis. The tests
conducted can vary, but tend to include fluid cleanliness, viscosity,
acid number, water content, elemental analysis, analysis of oxidation,
and ferrography. Together, these tests can identify the beginning of a
wear problem and can even be used to identify root causes before the
gearbox sees catastrophic failure due to wear damage. Tests that indicate
the level of insoluble particles due to varnishing or foam can also
indicate problems from incompatible fluids being used to top off or fill
after a drain. Savant Labs offer many of these tests.
The effectiveness of fluid testing was demonstrated in a research project
conducted by NREL. The wind turbine gearbox under test installed for
operation at a wind farm saw some temperature excursions above 90 °C, as
well as two fluid loss events. Researchers were able to determine based
on the laboratory analysis of the fluid that the gear teeth were wearing
abnormally after just 300 hours in service. This was later verified by
visual inspection after the field-testing component of the project was
complete. The researchers were able to retain the gearbox for the
remaining stage of testing because they removed it prior to catastrophic
damage (Sheng et. al., 2011).
Another benefit of periodic fluid testing is the ability to assess
whether a fluid drain interval can be extended in a particular case. A
five-megawatt wind turbine can require 700 gallons of lubricant, and
costly synthetic fluids are preferred in the industry. Typically,
oil change intervals are scheduled for from 9 to 16 months. In a
project conducted by OELCHECK and Fraenhofer Institute for Wind Energy
Systems (IWES), a gearbox in a wind turbine installed in the field using
a polyalphaolefin (PAO) was monitored for almost four calendar
years. Only slight degradation was seen in the fluid as a small
reduction of additive content and increase in oxidation
products. The fluid could continue to be used without replacement,
despite the long interval (Coronado and Wenske, 2018).
Savant Provides
Fluid Testing Programs
The cost of implementing a fluid testing plan that coincides with regularly
scheduled maintenance on a wind turbine installation is minimal compared
with the costs of waiting until a failure becomes catastrophic to find it
or changing wind turbine fluids more often than necessary. With
Savant Labs as the laboratory partner in a fluid testing program, a wind
turbine operator would have years of testing expertise, rapid test
turnaround, continuous communication, and a quality guarantee
statement. Savant Labs are an enthusiastic and capable participants
in supporting the growth of wind energy generation.
Because Quality Matters
Savant is positioned to offer some of the most precise data found in the
industry to date. Regular instrument calibration and maintenance to
meticulous reference values and control chart monitoring is part of the
quality regimen. In addition, all test results undergo a stringent
quality review process, data is delivered on time and reported via
email in a logical format designed for easy interpretation.
Request a quote or contact us to discuss your next lubricant testing project.
References
- US Energy Information Administration (EIA), “International Energy Outlook 2021: Data tables (2020 – 2050).” Released October 6, 2021. Accessed: May 9, 2022.
- US Energy Information Administration (EIA), “Wind Explained: Electricity generation from wind.” Last updated: March 20, 2022. Accessed: May 9, 2022.
- Coronado, Diego and Wenske, Jan, “Monitoring the Oil of Wind-Turbine Gearboxes: Main Degradation Indicators and Detection Methods,” Machines, vol. 6, no. 25, 2018. Accessed: May 9, 2022.
- Sheng, S., Link, H., LaCava, W., van Dam, J., McNiff, B., Veers, P., Keller, J., Butterfield, S., and Oyague, F., “Wind Turbine Drivetrain Condition Monitoring During GRC Phase 1 and Phase 2 Testing,” October 2011, NREL. Accessed: May 9, 2022.
- Aikin, Andrea R., “Bearing and gearbox failures: Challenges to wind Turbines Tribology and Lubrication,” Tribology and Lubrication Technology, Aug 2020, pp. 38 - 39. Accessed: May 9, 2022.