Wind turbines endure some of the most extreme environments—from hurricane-level winds to turbulent seas and broiling deserts. To maintain reliability, oil analysis and filter debris analysis (FDA) are vital to wind turbine reliability programs.
The average failure rate of a single offshore wind turbine is an astounding 8.3 failures per year. A common cause of failure is contaminants such as wear debris, rain, sand and moisture intrusion. By consistently monitoring lubricants and conducting periodic FDA, most of these issues can be identified and resolved before serious damage occurs.
The wind industry norm for oil condition monitoring includes a regular review of the main turbine gearbox oil and the hydraulic system fluid for basic property analysis, degradation contamination and wear. Much of this oil sampling and testing is performed not only to verify the condition of both the oil and equipment, but also to satisfy the requirements of the system warranty. About 75% of customers sample and test the oil every six months. The remaining 25% review the oil on a more frequent basis—at least once a quarter.
Lubricant Analysis
While occasional oil and grease testing can offer some advantages, it is the continuous, trend-focused approach that truly reduces equipment downtime, streamlines maintenance and safeguards warranty claims.
Components that should be tested include the following:
Turbine Gearbox
- High loads and stress: The gearbox transmits large amounts of torque, making it susceptible to wear and fatigue.
- Contaminant intrusion: Particles, water and other contaminants can quickly degrade the lubricant, leading to accelerated component damage.
- Early fault detection: Ongoing analysis helps identify gear or bearing wear before it escalates into costly failures.
Hydraulic Pitch System
- Precision requirements: The pitch system fine-tunes blade angles to optimize power output. Contaminated hydraulic fluid can reduce responsiveness and increase the risk of control failures.
- High pressure operation: Hydraulic components operate under significant pressure, making them vulnerable to small amounts of wear debris or water contamination.
- Reliability and safety: Loss of pitch control can lead to unsafe operating conditions or major mechanical stress on the turbine.
Drive Gears: Pitch and Yaw
- Frequent adjustments: Pitch and yaw drives constantly move the blades and nacelle to track wind direction, causing mechanical stress and continuous gear movement.
- Wear detection: Regular lubricant checks reveal wear particles, helping maintenance teams address issues in gears and pinions before they fail.
- Reduced vibration and noise: Proper lubrication and timely contaminant removal lower vibration levels and extend the life of critical components.
Bearings: Main Shaft, Generator, Pitch and Yaw
- Critical support: Bearings support rotational loads and keep shafts aligned. Inadequate lubrication accelerates wear, eventually causing turbine downtime.
- Heat management: Bearings run at high speeds and may experience friction-related heat buildup. Clean, functional lubricant is central to proper heat dissipation.
- Extended service life: Routine oil or grease analysis allows for proactive bearing maintenance and replacement, preventing unplanned outages and costly damage.
Ultimately, regular lubricant analysis is crucial for these wind turbine components due to their continuous high-load operation and exposure to harsh environmental conditions.
Tests should include the following:
- Water Content (Karl Fischer Water) D6304
- Acid Number (TAN) D974
- Viscosity D445
- FTIR Spectroscopy E2412
- Particle Count (ISO 4406:99)
- Ferrous Wear Concentration
- Analytical Ferrography (Analytical Ferrography should be automatically performed on all abnormal machine conditions.)
- Wear, Contamination and Additive Metals (Elemental Spectroscopy) D5185 (Ferrous Wear Concentration, Analytical Ferrography and ICP Spectroscopy are recommended for grease as well.)
Reliability teams should anticipate a comprehensive report detailing the in-service condition of the lubricant as well as the type, origin and severity of wear and contamination. Each finding should also include a technical interpretation for proper context.
Filter Debris Analysis
Up to 95% of the wear debris that could reveal critical information about the condition of the wind turbine is lodged in the filter and never makes it into an oil sample. This is due to the fact that wind turbines use increasingly finer filtration to ensure longer life cycles and compensate for greater performance demands on the machinery.
However, this means that the only particles that can be analyzed with conventional oil analysis are those that are already present in the oil and are smaller than the filter’s pore size (or those that are introduced into the oil before filtering). So once the filter is discarded, the potential insights are discarded along with it.
In addition to picking up wear debris caught in the filter that an oil sample would miss, here are some justifications for filter analysis:
- To gauge metallic wear generation rates of machinery components
- To determine the size and quantity of abnormal metallic wear debris particles
- To determine the exact elemental makeup of wear debris captured in filters
- To make operational decisions about critical assets
- To round out an existing oil analysis program
By analyzing filter debris, the lab can pinpoint contaminants and wear indicators that are either removed from the oil by the filter or are too large to be detected by traditional elemental analysis.
The Hidden Costs of Varnish
Varnish contamination in machinery can introduce a range of costs that may not be immediately obvious. Beyond the direct expense of cleaning or replacing contaminated components, here are some hidden ways varnish can increase the cost of operation:
• Decreased Efficiency: Varnish deposits can coat moving parts and reduce system efficiency, raising energy usage and operational costs over time.
• Unplanned Downtime: When critical components become coated with varnish, equipment may require emergency shutdowns for cleaning and repair, leading to costly production losses.
• Accelerated Wear and Tear: Varnish buildup can trap contaminants and restrict lubricant flow, accelerating wear on bearings, gears and other wind turbine parts, ultimately shortening the life of the turbine.
• Increased Maintenance Demands: Frequent filter changes, more frequent oil changes and additional cleaning procedures all add extra maintenance labor and supply costs.
• Warranty Complications: Excessive varnish contamination can void or complicate certain warranty claims if manufacturers determine that proper fluid care or preventive measures were not followed.
• Safety Risks: In severe cases, varnish buildup may cause parts to stick or lead to sluggish system response, increasing the likelihood of operational hazards.
All of this is especially troubling for wind turbines because of the high cost of unplanned downtime and accessibility issues that drive up the cost of repairs. Addressing varnish issues early, through proactive lubricant monitoring and contaminant control measures, reduces these hidden costs and protects machinery investments over the long term.
The Method
The lab will clean and examine the filter methodically using a self-contained FDA instrument. First, the filter will be placed in the system wash chamber, where fluid and compressed air are used to clean the filter of any debris. The filter debris-containing wash will then be collected and analyzed.
While there are unique logistical issues with FDA for wind turbines—the most glaring being the size of the filter and the difficulty handling it—experts recommend testing all used filters before they are discarded. Ultimately, the filter element holds a wealth of historical diagnostic information that has been accumulated over the entire service life interval. Having access to that data proactively could mean the difference between seamless operation and unplanned downtime.
Advanced Lab Services
When a sample pulled from a lubrication system has concerning anomalies, routine oil and filter analysis is not enough. Advanced tests for wind turbines may include the following:
- Material Identification Analysis: Material Identification analysis (MIA) is a forensic-level service that includes an in-depth investigation to identify the root cause of an issue and/or the origin of foreign material. The analysis incorporates various analytical and sample preparation techniques that lead to recommendations for resolution.
- Compatibility Analysis: Mixing incompatible lubricants is common. However, it creates issues such as excessive foaming, formation of precipitates or deposits, and loss of key performance characteristics such as water separability. ASTM D7155 Standard Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils should be used as the guideline for compatibility testing.
- Varnish Potential Analysis: Varnish is an insoluble film that coats internal components and can devastate wind turbine operations. The debilitating effects of varnish are well documented. The complexities associated with detecting varnish potential render routine oil analysis ineffective in reporting varnish. Varnish Potential Analysis testing monitors the contaminants responsible for varnish and alerts customers on when to implement appropriate, corrective actions before costly damage occurs.
Given the expense of replacing the following wind turbine components, regular lubricant analysis and periodic FDA just make sense. The following figures are conservative estimates for a five-megawatt wind turbine:
- Blade: $391,000-$547,000
- Blade bearing: $62,500-$78,200
- Gearbox: $628,000
- Generator: $314,000
- Electronic modules: $16,000
For all machinery—and especially expensive machinery such as wind turbines—the cost of condition monitoring pales in comparison to the cost of damaged and destroyed components that lead to downtime. Wind turbine operators should look for a lab that can efficiently process and analyze routine samples and produce a straightforward report that quantifies machine health, lubricant condition and contamination.
Al Yates is the vice president of Eurofins TestOil. He is responsible for leading the industrial and transportation sales team. With valuable experience in robotics and automation, he creates workflow automations that lead to company-wide efficiency.