Energy security and sustainability are headline topics – soaring gas and electricity prices and growing concerns about climate change have guaranteed that. Part of the answer is an increased focus on wind power; as a result, it is significantly growing in importance as part of the UK and the world’s overall energy mix.

The UK government has committed to a major expansion of offshore capacity by 2030, raising the target from 40 GW to 50 GW, with 5 GW from floating offshore wind sources. Good progress is already being made. In July this year, the government approved 8 GW of offshore wind capacity – a major milestone for renewable energy and a significant step toward the UK meeting its net zero and energy security commitments.

All this activity is having an impact: the offshore wind industry is on the cusp of a major transformation, fueled by increased demand for clean energy, technological advances and improved efficiencies.

Keeping pace with industry trends

Given the scale and importance of the task, it is essential for the wind industry to unite around an agreed set of standards and practices, which is where Denmark-based APQP4Wind comes in. The non-profit organization was founded by world-leading wind turbine manufacturers and suppliers to help ensure that performance improvements keep pace with the downward trend in the levelized cost of energy (LOCE).

Advanced product quality planning (APQP) is a well known concept within the automotive industry and has been the backbone for improving quality performance for manufacturers and suppliers for decades. In the context of APQP4Wind, the idea of APQP has been adapted to deliver a standardized framework of procedures and techniques that fit the specific conditions of the wind industry. As a result, APQP4Wind has become an important seal of quality in the wind energy sector.

Optimizing turbine performance

Unlike other industries, wind turbine operators are well aware of the critical role played by lubricants in machine performance. To sustain maximum power output, it is critical to reduce unscheduled and costly downtime for maintenance and repairs. And to do this with ever more extreme temperature, load and water contamination conditions that are common in offshore installations.

That’s why the Mobil brand joined APQP4Wind; we support its championing of common quality standards across the industry and embrace its framework in our ongoing product and service development. Our close collaboration with the world’s leading OEMs helps us understand equipment trends and lubricant requirements, consult on lubrication system designs, and troubleshoot field lubrication challenges, expertise that we are sharing with APQP4Wind.

Mitigating bearing failures

For example, white etching cracking (WEC) is a common cause of bearing failure in the gearboxes of wind turbines. The condition, which gets its name from the appearance of the white fissures in the microstructure of steel, can result in critical parts failure. Given that the cost of repairing a wind turbine gearbox is expensive, compounded with the associated loss of productivity, it is little wonder why multiple investigations have been conducted to determine the cause of WEC.

To date, no definitive trigger has been established, although WEC is most likely the result of a complex interaction between mechanical, electrical, operational and chemical factors. This tribochemical reaction – the chemical changes that occur to a lubricant and a lubricated surface – is not well understood, so the Mobil team and a major bearing manufacturer set out to compare a range of lubricant formulations to a reference oil that has been reported to generate WEC in bearings.

The findings were then used to help formulate Mobil SHC Gear 320 WT, a synthetic gearbox oil that has been awarded a Conformity Statement by DNV GL, verifying that it does not contribute to the formation of WEC. It is also supplied with a 10-year warranty.

A new spin on wind turbine performance

The wind industry also requires long-lasting greases that protect against wear, rust and corrosion, even in extreme conditions. Formulations using a metallocene polyalphaolefin (mPAO) base stock have demonstrated superior low-temperature performance compared with greases made with mineral and cPAO base stocks in lab tests.

Checking a lubricant’s formulation and ensuring it is the most effective could help enhance the overall reliability and protect individual components. Operators should also ask for gearbox flush and fill guidance, as well as start-up and cleanliness advice from their lubricant supplier. Used in combination with dedicated wind turbine oils and greases, these can help wind farm operators achieve superior equipment protection and long service intervals, generating safety, environmental and operating cost benefits.

The wind industry is set for growth. To maximize the opportunities this will bring, operators need to observe optimum maintenance standards to help safeguard uptime. Best practice standards, in combination with advanced lubricant solutions, can help turbine operators enhance operations and deliver the renewable energy we all need.

Conor Wilkinson is the EAME Commercial Brand Manager at ExxonMobil, responsible for a range of Mobil solutions for the commercial sector. Conor has extensive experience in Brand Marketing, Strategic Planning, Technical Solutions & Sales Management and was formerly the Europe Energy Sales Manager with a customer base across conventional, renewable, and decentralized power generation. Conor began his career in 2009 as a field engineer in the UK, providing technical services to customers in the energy and manufacturing sectors. He is a native of Ireland and graduated from Queen’s University Belfast with a Masters of Chemical Engineering.

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When it comes to the equipment inside wind turbines, performance and reliability can’t be compromised. Turbines are often in remote locations like mountaintops and offshore outposts. They must be built to withstand very harsh and dynamic operating conditions. They’re relentlessly pounded with weather extremes including oppressive heat, freezing cold, hail, rain, snow and the very wind they’re designed to harness. It’s up to operators to maintain turbine performance against all odds, and one way to do that is by ensuring proper lubrication.

Lubrication keeps turbines in motion

There’s a lot to be said for lubrication in the right amount, at the right time, applied consistently over the life of a machine. Bearings and other components simply last longer. Grease collars form to keep dirt and moisture out. Blown-out seals are less likely. Lubrication not only protects the system – it keeps it in motion and helps reduce waste caused by over-lubrication along the way.

According to the Global Wind Energy Council, global wind power capacity grew 275% from 2010 to 2020 and is projected to grow another 63% by 2025. One factor driving that growth is that the cost per kilowatt-hour of wind power has steadily dropped. To maintain this positive momentum and remain competitive, wind turbine operators today must rely on solutions to reduce friction, increase energy output and minimize maintenance costs.

Turbines of any size require significant maintenance to keep them performing to their fullest potential. That’s where automatic lubrication systems come in. For any turbine larger than 2 MW, a lubricating system is becoming standard, and it’s a must-have for anything offshore.

Four reasons to invest in automatic lubrication

Automatic lubrication options have changed the game for wind farm operators. Here are a few ways automatic lubrication systems prove they’re worth the upfront investment.

1. Improved safety. Manually lubricating turbines can be a hazardous task. A turbine’s most important internal components are situated where winds are strongest – as high as 400 ft. Offshore units present additional challenges if maintenance crews encounter rough seas. Today, automatic lubrication pumps and systems take human beings out of risky situations by automatically dispensing precise amounts of grease at regular intervals to reduce up-tower labor compared to periodic manual greasing.
2. Reduction in downtime. Manual lubrication can be dangerous and tedious. Using a grease gun to lubricate each moving part in the turbine is a time-consuming job. Turbines operate 24/7, and stopping them to allow service technicians to lubricate bearings and other components interrupts the power supply they produce. With an automatic system, lubricant is applied while the system remains in motion. It also removes human factors, such as under- and over-lubricating or, even worse, completely neglecting lubrication.
3. Maximized turbine life. Automatic systems can also improve the performance and extend the life of pitch, yaw, mainshaft and generator bearings. Further, moisture inside a turbine gearbox can be a significant issue, leading to corrosion. However, component failures due to mixing and contamination of grease with dirt and water are reduced with automatic lubrication systems in place. This leads to fewer maintenance issues, which is especially helpful for reducing the number of times offshore operators have to ship out a vessel to make repairs.
4. Material savings and efficiency. Investment in a system vs. manual lubrication not only reduces labor costs, cuts risk and extends equipment life, but it can also ease waste and environmental challenges due to greater precision. Less grease reduces the environmental impact from grease waste. Grease spreads better across the surface while the moving parts are in operation, a further advantage of the automatic system. The increased efficiency and quality of application allows the system to use a smaller and more precise volume of lubricant at each maintenance interval.

The future of wind turbine maintenance

Thanks to innovations like automatic lubrication systems, wind power has become more reliable and more affordable than ever. American Clean Power reports that wind power was the No. 1 choice of utility-scale power generation in 2020, and together with solar delivers nearly 11% of the nation’s electricity. Additionally, per American Clean Power, wind costs are 70% lower since 2009 – thanks to considerable investment in improvements by all members of the wind power industry. Still, it’s a young industry with tremendous upside. As demand continues to rise for renewable energy sources, automatic lubrication systems will become even more vital.

Hans Landin is group vice president and an officer of The Timken Company, a global industrial leader in engineered bearings and power transmission products. Hans leads the successful integration and growth of business units that engineer, manufacture and sell lubrication systems, linear motion products, industrial belts, chain, couplings, clutches and brakes. With its Groeneveld and BEKA brands, Timken is the world’s second-largest producer of automatic lubrication systems for industrial applications.

In the early 2000s, Timken made a strategic decision to focus on problems occurring in the field. As wind turbines grew larger, bearing failures increased, sending ownership costs sky high. Turbines built to last 20 years needed major component rebuilds in as few as seven years, which can be very costly over the life of the turbine. By engaging power producers, OEMs and industry collaborators worldwide, Timken acquired and developed a powerful portfolio of products that’s now helping to move wind power forward.  

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There is an abundance of literature dating back over the past 20+ years about the challenge of premature gearbox failures, and the cost impact they have on wind turbine operation. While the principals of prognostics and health management (PHM) are well established, and the objective of replacing unplanned failure events with scheduled maintenance based on early indication of degradation has not changed, the wind industry and sensor technology continue to evolve in ways that steadily increase the value proposition.

With global acceptance of the need to shift our energy dependence to renewables, the demand for wind energy is driving the development of much larger turbines and a significant increase in offshore wind farms. The primary cost avoidance targets associated with PHM, or condition based maintenance (CBM) are tied to business interruptions, inspection and repair costs, along with downtime penalties. The larger the turbine, the more difficult to reach, the higher the cost and complexity associated with inspection and maintenance. Secondary or catastrophic failure events that cannot be addressed in-situ are even more concerning with taller, harder to reach and heavier components. Further, with greater dependency on wind as a primary energy source, the cost of downtime penalties is also likely to continue increasing.

Evolution of wind turbine size and output. Source: Liebreich

Wind turbine heights and rotor diameters have easily doubled since the early 2000s as the industry pushes the boundaries of production per turbine. With the emergence of offshore wind as a major source of energy, size will continue to increase the maintenance challenge. In 2019, General Electric installed the Haliade-X turbine prototype in the Port of Rotterdam. The wind turbine stands 260 m (853 ft) tall and has a rotor diameter of 220 m (721 ft). Vestas plans to install the V236-15MW offshore prototype at Østerild National test centre for large wind turbines in Western Jutland, Denmark, in the second half of 2022. The wind turbine is 280 m (918 ft) tall with a predicted production output of 80 GWh a year, enough to power nearly 20,000 households. The criticality of keeping the massive wind turbines of the future running and being able to efficiently maintain them based on condition will only increase in importance.

While wind turbine, gearbox and bearing manufacturers strive to design more reliable assets, the common phenomenon limiting useful life continues to be surface fatigue resulting from repeated stresses under bearing rolling contact or gear meshing contact. Excessive loads, misalignment, material flaws, manufacturing defects, mishandling, contaminants in the oil, high oil temperatures and corrosion are some of the potential contributors to localized damage that begin to degrade the bearing or gear. In other words, the reality is that even with more reliable bearings and gearboxes, there will always be a probability of failure over time supporting the value proposition of moving from reactive to proactive, condition-based and ultimately to predictive maintenance.

An offshore wind installation near Scotland

That desired future state of truly predictive maintenance is well articulated in the principal of “Maintenance 4.0” that is the application of “Industry 4.0” technologies (industrial analytics, automation, robotics, etc.) to operations and maintenance (O&M) activities. The business objective is to radically improve equipment availability while lowering O&M costs through digitalization. While much attention is paid to the advances in artificial intelligence as means to turn data into valuable insights, the often unspoken challenge is that insights are only as good as the data.

In the case of wind turbines, that data comes from sensors used to monitor the health of the bearings and gearboxes. Progressing toward predictive maintenance requires the ability to not just identify damage, but to determine damage severity and calculate time to failure or remaining useful life (RUL). This is where oil debris monitoring differentiates itself from other types of sensors, as quantifying the wear debris from a damaged component is a direct representation of the damage of the monitored component.

For wind turbine gearboxes, oil debris monitoring (ODM) technology provides an early indication of bearing spall and gear pitting damage and quantifies the severity of damage progression towards failure. Online oil debris monitoring provides the most reliable and timely indication of bearing degradation because:

• Bearing failures on rotating machines tend to occur as events and could be missed by means of only periodic inspections or data sampling observations.
• As large wear particles are being detected by the oil debris monitoring sensor, there is a low probability of false indication from benign smaller wear debris particles.
• Residual or wear-in debris can be differentiated from the actual damage debris because the accumulated particle counts recorded due to the former tend to decrease while those due to the latter tend to increase.

While ODM technology itself is a proven technology used in asset management across multiple industries, truly understanding the physics of failure to be able to develop the algorithms necessary to accurately predict RUL requires years of study. Ottawa, Canada-based Gastops first started conducting surface fatigue tests on bearings to understand the progression of failure in 1992, bringing ODM to the wind market in the early 2000s.

The company is now a world leader in critical equipment condition monitoring, having installed over 20,000 oil debris monitoring sensors on active wind turbines with a proven history of detecting early signs of damage in advance of failures, maximizing availability while minimizing downtime and maintenance costs. Realizing the goals of PHM, the technology is used to monitor drivetrain health, by detecting the initiation of damage and monitoring its progression, which enables maintenance events to be scheduled proactively, preventing costly unplanned downtime during critical operating periods.

The ability to determine the remaining useful life of an asset is critically important as it provides the necessary information for operators to optimize the operational lives of their gearbox and main bearing. The company’s flagship product, MetalSCAN, is an online advanced oil debris sensing technology which is plumbed into the return oil line from the gearbox or main bearing. Any debris generated within the gearbox passes through its core and is quantified in terms of size, frequency and the type of metal, whether it is ferrous or non-ferrous material.

This information is collected and compared against predefined warning and alarm limits, developed using customized algorithms based on the geometry of the gearbox. When debris passes through the sensor, MetalSCAN translates the information it gathers into the RUL of the gearbox or main bearing. This allows the operator to understand the current health, adjust operational parameters and plan maintenance activities, preventing the requirement for shutdown during critical operation periods.

While ODM provides an ideal data source to provide the valuable insights required to support predictive analytics, realizing the vision, and leveraging the potential of Maintenance 4.0 will require a variety of data sources in multiple locations to improve the accuracy of modeling, allowing operators to pinpoint failures throughout the system. Many wind turbine manufacturers already combine vibration sensors and ODM into the overall condition monitoring systems they provide.

As technology advances to enable the transition from condition-based maintenance to truly predictive maintenance, real-time equipment intelligence will be required. Systems that combine the information from next generation real-time sensors that monitor data on multiple factors such as oil debris, oil condition, vibration, temperature and pressure will be used to develop advanced analytics and digital twins. Connectivity to enable large scale IIOT deployments with the assurance of data security and network reliability will be key factors in enabling wind farm operators of the future to realize the vision of Maintenance 4.0.

Paramount to success in this evolution remains the intersection of machine intelligence with human ingenuity. The expertise that comes with decades of research into the physics of failure by a company like Gastops combined with a commitment to innovation and drive to realize the vision of real-time prognostics will lead to a future of optimized O&M costs in the wind industry. Today’s ODM technology is already providing the benefits of PHM envisioned 20 years ago. The rapidly increasing demand for wind energy is driving the creation of massive wind turbines that are being located offshore. There is a clear requirement to evolve condition monitoring systems to provide operators with PHM capability enabling the future of predictive maintenance.

Jordan Freed is the Director of Corporate Marketing & Product Strategy for Gastops Ltd, where he is responsible for product management, strategic growth and marketing.  With a Bachelor’s Degree in Electrical Engineering and over 25-years of experience, Jordan is a customer focused leader, passionate about innovation and product realization to address the future needs of the market.   His career spanned multiple industries including steel, telecom and defense prior to joining Gastops in 2020 to support the organization’s long term growth objectives.

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