August 2010

Increasing global reliance on wind energy means that more wind turbines are being built each year, and these massive structures require regular maintenance and repair. International Climbing Machines (ICM) has developed a remote-controlled device that provides a safe alternative to traditional methods for the inspection, repair, and maintenance of wind turbine towers and blades. ICM climbers are small (approximately 24” length x 24” width), lightweight (40 lbs.), remote-controlled devices that can adhere to steel, composite, ferrous, or nonferrous surfaces. They can access both wind turbine towers and blades and they are extremely flexible, maneuvering over obstacles like bolts and weld seams with ease. Moreover, ICM climbers have high payload capacity to deploy cameras, ultrasonic testing sensors, cleaning heads, coating removal tools, epoxy injection equipment, paint spraying guns, and other devices the job requires.

Current Challenges
Blade maintenance and repairs are rapidly becoming a considerable portion of a wind turbine’s maintenance costs. To keep them turning and producing at their optimum output, wind turbine blades need to be inspected and maintained regularly. Damaged, dirty, or faulty blades can reduce the overall productivity of a turbine and should be repaired and cleaned as part of the operator/owners preventative maintenance program. By carrying out a thorough inspection of the wind turbine blades each year, the owner/operator is reducing the risk of a catastrophic failure by highlighting issues early and taking action immediately. The damage is often found long before it spreads, allowing for a much smaller repair and ultimately less downtime. Figure 1

Wind turbine blades can be damaged or degraded by several factors. Working at optimum wind conditions, a blade tip could be turning at speeds well over 100 miles an hour. Over time sand, ice, rain, UV rays, and insects—just to name a very few—can have serious adverse effects on the leading edge. Lightning and bird strikes can also lead to serious damage and reduction in productivity. Over time the blade is subjected to a serious amount of damage, often starting with a small problem that if caught early enough could save a huge amount of money, downtime, and lost revenue. Blade inspections and regular maintenance are not a luxury, they are a necessity.

Current Approaches
Wind turbine towers and blades present unique challenges to “access” the surfaces. They are very high off the ground, after all. Until now wind turbine towers and blades have been serviced either by removing the blades and transporting them to a facility for repair, in the field using cranes or, in some cases, rappelling to allow workers access. In-house blade repair is costly and requires downtime. Repairs and services using cranes to lift technicians and loads is a common requirement for turbine operations and maintenance work. This work is performed in windy conditions, and at extreme heights. Conventionally, accessing the surfaces of the towers and the blades has been achieved by rappelling workers from the nacelle, or using cranes or “cherry pickers” to lift the workers and their equipment to the surface. This is expensive, dangerous, and time consuming.

Design Advantages
Due to the inherent danger of current methods for wind turbine maintenance, ICM climbers present a clear advantage by keeping the people making repairs on the ground instead of climbing the heights themselves, using what is essentially a gaming controller to guide a machine to do the work. Using cameras as virtual eyes in the sky, the operator can see what the climber is doing and remotely use it to make repairs, inspect for faults or cracks, and perform any other tasks they would otherwise be doing themselves. Because the ICM climber is a free-climbing device, it does not require any scaffolding or cranes, both of which are costly and time consuming. Figure 2

The ICM climber is not the only robotic device used to climb surfaces, but it presents many advantages over other devices. The ICM climber is held to the surface with a patented technology. Essentially, the ICM technology is an onboard vacuum chamber surrounded by a rolling, flexible, and locomoting seal. This exceptional approach achieves what no other method can: It establishes adhesion to virtually any surface, ensures the climber can negotiate weld seams, surface irregularities, etc., and it locomotes the machine with the seal itself, whereby all the force provided by the vacuum is transferred to the locomoting assembly. In short, this provides surefooted traction unlike any wheeled or tracked crawler where the method of adhering the device to the surface and the method to drive it are separate or individualized. With the ICM technology the vacuum seal around the chamber and the locomoting element are one in the same, and its advantages are significant and very real.

This unique adhesion seal allows the climber to scale ferrous or nonferrous metals, concrete, brick, and composites, etc. Magnetic crawlers are obviously limited to ferrous metals, but the ICM climber is unaffected by the degree of rust that may be on the steel walls. Magnetic crawlers are highly affected by the rust layer, to the degree where they can fall off the vertical wall if the rust is too thick. Moreover, magnetic-type crawlers often have a buildup problem where metal and ferrous particle debris accumulates on the magnetic wheels or tracks, rendering the vehicle ineffectual at adhering to the vertical surface. ICM climbers cannot and will not be adversely affected by rust or debris.

ICM technology also has the ability to transition from floor to wall, and from wall back down to the floor if needed, and it is conducive to attaching an array of tools and/or capabilities to the same climber. For example, it is feasible for the same ICM climber to have onboard camera, cleaning tool, EMAT sensor, and other UT sensors. Also, it is possible for tools to be attached, detached, and reattached with minimal time and/or exposure to workers. Figure 3

In addition, the manner in which the ICM climbers traverse the surface—rolling along at a speed that can be accurately and evenly controlled from 0 to 3 inches per second—makes them conducive for regular and uniform surface cleaning, scanning, and measuring. The other approaches, using an inchworm or “fasten-move-refasten” approach for traversing along a surface, are not at all favorable for surface cleaning, scanning, or measuring.

Plus, the ICM climbers are very lightweight since they are primarily constructed of carbon fiber and epoxy. The rolling seal elements are made of highly durable yet lightweight composites of closed cell foam wrapped around open cell foam. The base ICM climber weighs approx 25 pounds. The tools and capabilities then mounted onboard the climber always employ the most strict weight-shaving regimen to keep the overall weight as low as possible. Figure 4

ICM climbers are ideal for any type of work being conducted on wind turbine towers and blades. With the imminent growth of the wind energy market, and the growing demand for more-efficient and safe approaches, ICM climbers are proving to be the future for the field of wind turbine inspection, repair, and maintenance.  

The Tehachapi area is considered the birthplace of wind in North America, and as we celebrate the 30-year anniversary since the first turbines were installed you can expect to see more milestones. Repowering and new development will flourish thanks to the first-of-its-kind transmission line and a 20-year contract with Southern California Edison. It represents the largest wind energy contract ever signed by a United States utility.

Decades of Delivery
A number of wind farms call Tehachapi home, including Terra-Gen Power, enXco, NextEra, Cal Wind Resources, Coram, Oak Creek Energy Systems, GE Energy, AES, Mogul Energy, and Windland. It’s been three decades since the first wind turbines were installed in the Tehachapi-Mojave Wind Resource Area. It is considered one of the premier places in the nation for wind power, and one of the windiest places in the world. The winds average 14 to 20 miles per hour through the pass from one year to the next, and they vary with the terrain, season, and time of day. Average wind speeds approach nearly 9 meters per second (about 20 miles per hour). This places much of the Tehachapi Pass in wind power class 6 (these classes range from class 1, the lowest, to class 7, the highest).

The first turbines erected in Tehachapi were about 45-60 feet in height, and they produced about 25-60 kilowatts. Today they stand about 400-500 feet, producing about 1-2.4 megawatts. The area is enjoying a new breath of life thanks to the new transmission line and a 20-year contract with Southern California Edison and Terra-Gen Power for the Alta Wind Energy Center, 1,550 megawatts (MW) of wind energy development. It represents the largest wind energy contract ever signed by a United States utility, and it also means that wind developers have better access to the California grid and the ability to sell to multiple utilities.

It also represents a major hurdle since a group of visionaries installed the first machines in the early 1980s. Multiple generations of wind turbine technology are still up and running in Tehachapi. There are the single- and double-blade turbines that generate between 25 and 60 kilowatts, to the more modern three-blade turbines that generate up to 4 megawatts. It’s four generations of turbines with an installed capacity of about 785 megawatts.

A lot has happened since the first machines were installed. After overcoming numerous regulatory hurdles, SCE officially began the construction of its Tehachapi Renewable Transmission Project (TRTP). The first phase of the TRTP cost $1.8 billion and will ultimately result in a high-voltage transmission system capable of delivering 4,500 MW of clean energy into the Los Angeles metropolitan area, which is located about 100 miles south of Tehachapi. Executed power purchase agreements to date will allow up to 1,500 megawatts or more of power generated from new projects to be built in the Tehachapi area. It represents the first construction of a “public” transmission line that carries electricity generated at the park straight to the grid. This state initiative to upgrade the transmission out of Tehachapi began in 2008 and is expected to be completed by 2012. It has proved to be a catalyst for multiple projects including: Coram Ridge, consisting of 34 Vestas V90s, developed by Coram Energy Group & Brookfield Renewable Power; Windstar, consisting of four Gamesa G52s, 37 G80s, and 16 G87s, developed by Western Wind Energy; and Alta I-V, consisting of  both GE 1.5s and Vestas V90 Turbines, developed by Terra-Gen Power. The Windstar project, whose general contractor is RMT, will bring the first Gamesa turbines to the region. These projects are all slated to see construction begin in 2010.

According to SCE, the TRTP will allow them to more than double its wind energy portfolio and envisions connection of more than 50 square miles of wind projects in the region, which is triple the size of any existing U.S. wind farm area. Officials estimate that it will eventually provide 4,500 megawatts of electricity, which could make it the largest wind project in the nation. The new wind farms are expected to eventually comprise 1,750-2,000 turbines. Not only does this triple the size of any existing U.S. wind project, but it is also expected to outperform the world’s current largest wind farm. Phase 1 of the TRTP, which includes segments 1 through 3 out of 11 planned segment improvements, is expected to be completed in 2010. Figure 1

Randy Hoyle, vice president and head of wind development for Terra-Gen Power, LLC, has this to say. “Terra-Gen Power is excited to be the first renewable energy company to utilize Southern California Edison’s (SCE) newly constructed Tehachapi Renewable Transmission Project. The 720 MW first phase of the project will increase California’s installed wind capacity by nearly 25 percent and contribute substantially to the state’s renewable energy needs.”

The transmission line has definitely strengthened the industry here. “According to the Kern County assessor’s office, by the year 2030 the wind industry will have assessments equal to that of the oil industry in Kern County,” says Linda Parker, executive director of the Kern Wind Energy Association. “This is a big deal. We never imagined when we started that we would rival the oil industry.”

The approval of the TRTP is a notable exception to difficulties with long-distance transmission in America. In fact, it’s the first major transmission project in California being built specifically to access renewable generators in a remote, wind-rich resource area. “Prior to that system coming we weren’t growing, and we weren’t going to. We couldn’t take one more watt,” says Parker. “The construction of the transmission line is a major accomplishment that many people have worked tirelessly on. It gives the wind industry options and the ability to contract with other electric utility companies.”

Collaborative Construction
Numerous entities, companies, and individuals played a major role in the conception, planning, development, and approval process for the transmission project, which has involved a number of precedent-setting decisions, both regulatory and in the courts. It is showing the way and sets an example for other badly needed transmission infrastructure projects in this country. Hal Romanowitz, president and COO of Oak Creek Energy Systems, was one of these key players. He says it is important that transmission expansion facilities be well planned and scaled to serve the large regional needs if they are to succeed. Figure 2

“TRTP progressed from our local development and planning efforts into the state-wide planning, and on top of that it took five studies to get the right focus onto a solution that was good for the entire state, not just a limited group, and the TRTP that is being constructed is very good for serving a substantial range of clean energy projects and to the overall grid reliability as well,” Romanowitz says. “TRTP planning in California was the start of a superior process for regional planning that continues and which will ultimately do well for the electric needs of the state on a proper scale.”

“Getting the transmission expansion scaled to the proper level and getting the costs rolled into rates paid by users of the system is extremely critical,” he continues. “This is one of the biggest problems blocking transmission expansion success across the country. To be proper, such user funded expansion needs to be part of a regional transmission planning process so that the expansion is properly scaled and will best serve broad needs. One issue is that in some states users are strongly objecting to pay for transmission used to transport new renewable energy across their state to others in remote locations. A strong national transmission grid is critical for our country, however, and we are not getting what we need with so much provincialism.”

Edison is not the only utility involved. As other utilities embrace wind power, the recently completed Pine Tree Wind Project is another example to note. The Los Angeles Department of Water and Power just brought the Pine Tree Wind Project online after overcoming significant obstacles during the project development and approval process. In a project implementation process that began in earnest in 2003, LADWP has added 120 megawatts of wind to its distribution grid. “It’s another precedent,” Parker notes, “Los Angeles coming to Kern County for wind.” Figure 3

The Pine Tree project is able to deliver energy directly into existing LADWP transmission system lines that already run through Kern County to bring in hydro-electric power from points north. In these times of droughts and reduced production from hydro projects, it’s a great match of complementary clean technologies.

A key player in this project is AECOM, a global leader in renewable energy. The international consulting firm assisted LADWP with implementation of the Pine Tree project by conducting the initial resource surveys and constraints analyses, preparing environmental documents meeting both federal and state laws, preparing applications, and providing assistance to LADWP to obtain regulatory and land use permits. The firm also provided resource monitoring support and compliance services during project construction. Prior to the beginning of construction, LADWP had to secure 12 regulatory permits containing nearly 400 separate mitigation measures and conditions of approval.

“The development process for Pine Tree had to face numerous regulatory challenges, including endangered species, federal, state, and local agency involvement, military flight corridors, and a lawsuit by an environmental group,” says Jane Chang, an environmental planner in the Irvine, California, office of AECOM.

Power Permitting
Though the process of permitting wind energy in Kern County has been generally good, like anyplace Tehachapi has its share of permitting issues like anyplace, and they’re getting even tougher according to Ed Duggan, executive vice president of Oak Creek Energy. “The biggest challenges facing wind energy development in Tehachapi and elsewhere in California are environmental concerns that seem to be running somewhat amuck and government agencies that are afraid of being sued as a result.”

For example, the recent success of the California condor breeding program has resulted in concerns about this endangered species expanding into the Tehachapi Wind Resource area, and this has resulted in recent calls to restrict development here.

“If it’s not the condors on the mountain ridges, it’s the desert tortoise and ground squirrel on the flats,” Duggan says. “The problem is that some environmental groups seem to be focused on single issues and not looking at the big picture. The reality is that there are risks and consequences from all types of energy generation—just look at the environmental disaster in the Gulf of Mexico being caused by oil right now.”

We need to push permitting agencies to look at the big picture and factor in the national security benefits of home-grown energy and the potential of mitigating global warming, and job creation. Luckily, the county and the community seem to get the big picture. “One of the great things about Tehachapi is that the wind industry has been here for so long now that we have a lot of people rooting for us,” Duggan observes. “The businesses, residents, and government leaders have long recognized the benefits of wind.” Figure 4

It’s this support from government officials, residents, and stakeholders that has allowed companies such as Oak Creek Energy Systems (OCES) to endure the real test—time. OCES is a wind energy pioneer that began in the early 1980s and developed one of the first projects in the Tehachapi area. The company has long played an active role in the wind energy industry and was instrumental in advancing wind progress and policies. Steve Cummings, who is my father-in-law, is the former president and founder of Oak Creek. He installed some of the first wind turbines in Tehachapi, and in North America for that matter. He was also the first president of the Kern Wind Energy Association.

He describes some of the hurdles his generation faced. “At that time there wasn’t a lot of product availability, so you had to take what you could get,” he says. “You may want a certain turbine, but it might not be available for more than a year. The American manufacturers had to play catch-up since the Danish had a head start. Plus we not only had to import turbines from other countries, but we had to bring the technicians over, too.”

Avoiding Conflict
Tehachapi leaders were also the first to realize that proper planning and engaging stakeholders would help preclude conflict, and today we all benefit from the ongoing public dialogue that started back in the 1980s. “The county was fairly easy to deal with back then,” says Jim Watkins, a wind energy consultant and one of the early pioneers in the Tehachapi wind industry. “Since this was unprecedented there weren’t any guidelines, so they established an ad-hoc committee that consisted of people from the wind industry and environmentalists, which proved to be very helpful,” he says. “Since this was all agricultural land we had to create new guidelines and zoning, and we didn’t have a model to follow—we had to create the model.”

Of course the federal and state tax credits played a major role in spurring the wind energy industry back then. Some of the first companies include Zond, Oak Creek Energy, WindLand, Windridge, SeaWest, Difko, FloWind, Cannon, CalWind Resources, Mogul Energy, and AB Energy, just to a name a few, although many of these original companies have sold or changed their name.

“For the first four years it was all about the tax credits, and when they expired this was a major setback,” Cummings recalls. “The machines could not stand on their own. Since no one had contracts with SCE, we had to hammer these out. In my mind this was the most challenging aspect. It wasn’t so much an infrastructure issue since they were able to carry the loads we were producing pretty easily. It was more of a negotiating issue. Initially there was a lot of discontent between the wind industry and Edison. I can remember our first dealings well. A question would come up and we didn’t have an answer. There were long moments of silence in those meetings when no one knew what to say. This was new to everyone.”

Pioneers like Cummings definitely paved the way. Thanks to the concentration of wind, its second largest industry, Tehachapi has been responsible for impacting the wind power industry on a national and global level. Founder of Zond—a Tehachapi-based turbine manufacturer that was acquired by Enron and ultimately GE—Jim Dehlsen and his son James went on to establish Clipper Windpower, which has become a major turbine manufacturer worldwide and is one of few American-based manufacturers. Figure 5

In addition to manufacturing, Tehachapi has spurred construction businesses including Wind Energy Constructors and World Wind Services, whose CEO is a second-generation wind power entrepreneur and is one of the few women owned business in the industry, as well as the highly acclaimed wind technician training facility, Airstreams Renewables. “More capacity and less impact are the key changes since wind was introduced here,” says Parker. “I should point out that yesterday’s technology is not today’s technology. We have fewer turbines that produce more energy, yet we have fewer access roads and intrusions to the land. Since the 1980s we’ve progressed to a technology that’s competitive with the rest of the world.”

What does the future hold for this wind-rich region? Repowering and new development are sure bets. Duggan breaks it down: “Oak Creek is an example of a wind project that is repowering and producing more energy as a result,” he says. “This repowering of smaller turbines with bigger, more efficient turbines has been going on for over 10 years now and it will continue at Oak Creek and on other older existing wind farms until most of the early eighties generation of turbines, which are now approaching 30 years in age, have been replaced.

“The potential upside of newer, bigger, better turbines is too great to ignore. As far as new development goes, we’ll see a lot more on the Mojave side of the Tehachapi Pass and a little more on the Tehachapi side, but much of the new capacity will also be in the nearby Antelope Valley area,” he says. “This region will grow to about 4,500-5,000 megawatts of total capacity in the next 5-10 years; it’s going to happen quickly. After that we’ll continue to expand at a slower rate, and by the year 2040 we should be somewhere around 10,000 megawatts of total capacity.” Figure 6

Future Developments
A look back reveals that some of the same challenges we faced then are the same challenges we’re facing today—regulatory hurdles, environmental concerns, costs, and negotiating with the utilities. Another thing that isn’t expected to change—expect Tehachapi to continue to lead the way when it comes to both wind power and solar. The rapidly expanding list of solar power project applications and plans includes as many as 63 developers because this also happens to be one of the four best regions for solar development in the world. The actual amount of proposed or planned wind projects is hard to ascertain, but some reports suggest this area could accommodate more than 40,000 megawatts of proposed renewable projects. That’s two thirds of California’s grid capacity and enough electricity to power more than 20 million homes.

Note: A Tehachapi native, Cummings is currently serving as president on the board of directors for The Wind Energy Center and a board member of the San Diego Chapter to Women of Wind Energy. She was also one of the nominees for the 2009 Rising Star Award for the Women of Wind Energy Association. 

A renewed focus on renewable energy has global competition heating up again for manufacturers seeking to do business with the wind power industry. There are approximately 8,000 parts in a typical wind turbine, ranging from large-scale gearboxes and blades to electronics, bolts, and fasteners. Nearly 50 percent of wind power components are made domestically, and while other parts are being produced in Europe, India and China are gearing up their capacity for manufacturing as well.

To repair a major wind power component in the field is an expensive line item. The price to repair or replace rotor blades, a gearbox, or a generator for a typical 2 MW wind turbine can be in the range of $350,000-$450,000. Given the staggering cost, wind turbine manufacturers are very reluctant to change their manufacturing process or embrace a new supplier or technology unless there is clear evidence of its impact on maintaining quality.

Hexagon Metrology—a prominent manufacturer of manual, stationary, and portable metrology solutions—has tracked measurement/inspection trends and strategies in the wind power business from the very beginning. The company leverages their broad internal expertise to help OEMs achieve critical quality control goals. As a result their acumen and knowledge base grows as metrology is applied successfully to solve problems unique to the alternative energy industry. Figure 1

Both stationary and portable coordinate measurement machines (CMMs) have a sound track record of ensuring dimensional control. For instance, wind turbine components such as blades, towers, flanges, nacelles, and cast and forged parts are inspected with portable arms and laser tracking systems. High-tech components like gears, gearboxes, and generators require higher accuracy that coordinate measuring machines provide.

And there are multiple layers of measurement and inspection processes being integrated into the design, production, alignment, and assembly of wind power systems. We will now take a look at three manufacturers who have solved formidable quality control challenges with metrology solutions and engineering know-how.

Verifying Transmission Housings for Wind Turbines
TVL (Toeleveringsbedrijf van Landuyt) in Wetteren, Belgium, finishes thousands of transmission housings for wind turbines each year. The housings are produced with high-precision machined bores with diameters of up to 64.5” (1640 mm). The tolerance for a 25.6” (650 mm) bore is ± 25 µm (±.001”), and this feature must be verified on every single unit. The bores are drilled at 0.08 percent of nominal diameter size.

“We could not measure big transmission housings in-house, so we worked with a service provider in Germany with the necessary equipment,” says Managing Director Geert Van Landuyt, adding that as production quantities grew, transportation to the service provider became a very costly proposition. “Ultimately, we needed our own coordinate measuring machine.”

Today, each four-ton transmission housing is verified on a Leitz PMM-F high precision CMM. The housings are measured in a room with the identical temperature conditions as the shop floor. This environmental control eliminates the usual waiting times required when parts must adjust to ambient temperatures in a thermally-controlled metrology lab.

The CMM’s monolithic gantry design has a length of 14.6 ft (4.5 meters), a width of 14.2 ft. (4.36 meters), and a height of 16.5 ft. (5.09 meters). The machine has a measuring volume of 118” x 78.7” x 63” (3000 x 2000 x 1600 mm). The U-formed CMM body is made of gray granite, which does not absorb as much humidity as black granite, contributing to better overall stability of the measurement results. Figure 2

TVL transmission housings are transported with a crane to the CMM. The measuring process begins once the automated alignment of the component concludes, and the part’s temperature is read by the CMM. The actual temperature of the housing is applied to the inspection program’s data points and evaluations, thus ensuring the same measured points are taken at arbitrary temperatures each time. The entire measurement process takes about 30 minutes and includes control points in nearly inaccessible areas of the housing.

Metrology-Assisted Steel Profile Cutting
Dutch company HGG specializes in steel profile cutting and manufactures bevel cutting machines that are particularly suitable for processing large components. EEW, a German manufacturer of wind turbine components, placed an order with HGG. They needed to manufacture foundation structures (also known as tripods) using high-quality steel for an offshore wind farm. The task was to produce cylindrical members cut precisely in 3D from 400 ton steel tubes that were 196.9 ft (60 m) long x 19.7 ft (6 m) high.

HGG recognized from the beginning that adopting the correct measuring technique would be the key to the success of the project. “We like challenges,” says Peter Tool, HGG R&D manager. “Our greatest strength is that we design our systems and software from the bottom up, so we retain flexibility. Short channels of communication allow us to come up with completely new processes in very little time.”

A tube weighing 400 tons deforms under its own weight when placed on the cutting machine. This deformation changes the diameter of a tube by up to 0.787 in. (20 mm) and leads to undesirable drifts. However, the changes in diameter are not constant. When the tube rotates on the cutting machine its ovality varies with the movement of the tube. In addition, a 196.9 ft. tube sags nearly three inches at the mid-span between supports. The structural frame of the cutting machine also deforms while supporting the extremely heavy load. In the face of deformations like these, even the most accurate machines are incapable of delivering a clean cut.

And mistakes can be very costly. Each tube comes with a price tag of roughly $57,000. “With expensive material like that, cutting errors cannot be allowed to happen,” Tool says. He and his team wanted to integrate a measuring system into the cutting machine. Their main premise was that the user should know the position of the tube relative to the cutting machine at all times. If the exact coordinates and deformation of the tube on the machine were always known, it would be possible to continuously compensate for the movement of the cutting head. Tool found a suitable method of control by coupling a Leica Absolute Tracker with the cutting machine. The high precision laser tracker could not only ensure the necessary accuracy, but had the required measuring range (up to 524.9ft) for the 196.9 ft. long tubes.

“From the start, we had one objective,” he says. “The machine had to be operated precisely by a single person.” HGG fully integrated the laser tracker into the cutting machine, so the operator did not have to operate the laser tracker. The instrument tracks several reflectors on the cutting head and on the tube. Every section of the tube is fitted with a reflector that tells the cutting machine operator how much the tube is bending. The laser tracker captures the 3D coordinates of one point every 100 milliseconds. Using the acquired data, the machine cuts the enormous tubes into individual sections, and to accuracies of a fraction of a millimeter. The cutting machine software also controls the tracker, which is a task made possible by the emScon programming interface developed by Leica Geosystems, a Hexagon company.

Dimensional Control of Rotor Blade Hubs
The main rotor hub is a very critical wind turbine component, as it transfers the rotors’ energy efficiently to the main bearing and constantly withstands enormous windload. The hub connects three blades to form the rotor and, depending on the model of wind power generator, is holding the motorized pitch mechanism for each blade. The rotor itself is joined to the slowly rotating shaft or main bearing with another flange, thus forming a rigid horizontal rotation-axis into the nacelles’ gearbox.

Diameter, flatness, and orientation of each hub flange are subject to very precise quality inspections. At Xinjiang Goldwind Science & Technology Company, one of the largest turbine manufacturers in China, a Leica T-Probe and a portable LTD840 laser tracker enables a single operator to quickly inspect and document the machined “as-built” part directly on the shop floor. Due to its wireless capability the probe can be utilized to measure hidden points without direct line of sight to the laser tracker. The system’s large 3D measurement volume (0 -131.234 ft.) enables the inspection of multiple interfaces and hubs with one set-up of the instrument. Figure 3

The probing device gives Goldwind all the advantages of a fixed CMM, but does not require a measurement lab and a time-consuming logistic process to move heavy parts to the CMM table. Previously, all those inspections were carried out using dial gauges, micrometers, and calipers. Mastered by experienced users, these instruments were very accurate but only provided two-dimensional information. Due to the increased size and numbers of parts to be inspected, the old manual process became a serious bottleneck for throughput and maintaining accuracy. Computer-aided design and modern quality management techniques in this competitive business set a new level of expectation, driving their need to implement a 3D metrology device for dimensional verification.

Metrology for Field Inspection and Beyond
Inspecting wind farm components at an insolated location has been difficult, or nearly impossible, with traditional measurement equipment. Introduced this year, a new line of laser tracker opens the door to remote field inspections for the wind power industry. The Leica Absolute Tracker AT401 was designed with serious portability features: small size, light weight, and long-life battery power combined with an IP54 rating and ultra-long measurement range of 525 feet (1050 feet radially). It is the first laser tracker that can be safely and easily used outdoors, even in the rain. The entire solution packs in case small enough to fit in an overhead luggage bin, giving quality control departments the mobility to follow wind power components from factory to field.

There are also new component developments underway that will significantly change the “manufacturing-to-metrology” landscape, from lightweight materials to longer life cycles for wind power parts. As the rotor size increases on larger turbines, the new designs will likely lean toward lighter, high strength, fatigue resistant materials. The step-up (geared) gearbox used on large turbines today is expected to be replaced in future turbines with direct-shaft-to-generator technology. The nacelle contains an array of complex machinery including yaw drives, blade pitch change mechanisms, drive brakes, shafts, bearings, oil pumps and coolers, controllers, and more. These are areas where simplification and innovation will become very important. Whatever the trend, quality control will play a critical role in the development and final production of wind turbine components.  

The outlook for M&A—mergers and acquisitions—activity in the wind energy sector is positive following a return to health in the second half of 2009 and 2010, according to a report by VB/Research. Wind is now established as the most mature renewable energy market, and it will be a major beneficiary of the continued drive by global governments to increase their domestic renewable energy capacity.

These conclusions are based on a worldwide survey of more than 250 senior executives active in the renewable energy industry conducted by KPMG and VB/Research, a specialist provider of renewable energy data, intelligence, and research. The survey was conducted between January and March 2010 and was completed by five different types of respondents: corporates, financial investors, debt providers, government bodies, and service providers. Among the respondents 75 percent were top-level executives such as chairpersons, senior executives, or divisional heads. Surveyed respondents were split among Western Europe (33 percent), North America (29 percent), and Asia-Pacific (18 percent), with Eastern Europe, Middle East and Africa, and South America accounting for the remaining. This research was supplemented by interviews with senior top-level executives from across the whole range of renewable energy sectors.

Signs of Recovery
In 2008 and early 2009 the effects of the financial crisis meant funding for new renewables projects slowed dramatically as lenders withdrew from the risky end of the market. The second half of 2009 and 2010 recorded a major increase in deal flow and volume. In the first quarter of 2010, global deal volume in the renewables sector increased by 245 percent. Wind was a major contributor to this recovery as the largest single renewable market, accounting for deals valued at $1.8 billion, just ahead of the $1.5 billion recorded for solar. This total was boosted by two big Iberian deals, with Enel and Iberdrola recently announcing investments of €860m and €320m, respectively, in wind assets in Spain. Deal flow has been steady since the report was completed in April. Since then the Brazilian investment fund Caixa Econômica Federal and the Argentine electricity provider IMPSA have invested $225 million to acquire a 45-percent stake in Brazilian wind generation power plant developer Energimp, while private equity firm Platina Partners have paid $95 million to buy 52 French wind farms from Infigen Energy. The wind technology sector has also been active in Asia, where the Chinese company Galaxy Semi-Conductor Holdings acquired the wind power equipment manufacturer Power Full Group Holdings through a deal worth $106 million.

Along with the two Spanish giants, other large project buyers in the wind sector over the last 18 months included the UK’s Renewable Energy Systems, Ireland’s Bord Gais Eireann, and North America’s NextEra Energy Resources. The U.S. also saw positive growth, as total wind energy capacity grew by 39 percent throughout 2009. The market in the States has been invigorated by an upsurge in wind investments from large utilities, such as Kansas-based Westar Energy’s acquisition of the development rights to a 500-MW wind project from Infinity Wind Power in January 2010.

The UK has been one of the greatest beneficiaries from the first wave of heavy government stimulus. The British government’s 2009 budget announced a series of support measures aimed at stimulating renewable energy projects including £525m for offshore wind farms through the Renewable Obligation scheme. Since this announcement a series of transactions have taken place as developers have sought to reduce their risk and attract third-party capital to their offshore wind commitments. Notable transactions included investment company TCW’s acquisition in October 2009 of a 50-percent stake in Centrica’s Boreas portfolio (total installed and projected capacity of 206-MW) along with a refinancing of the project. At the end of 2009, DONG Energy and Siemens Project Ventures acquired a 50-percent stake in Centrica’s 270-MW Lincs project. DONG Energy also announced the sale of a minority stake in its 367-MW Walney offshore wind farm project to Scottish & Southern Energy. The UK remains a highly attractive market boasting the largest wind resources in Europe and a well-defined subsidy regime.

Wind technology is lagging behind the sector at large. It has been impacted by weakening demand in the wind turbine market. The deep backlogs in turbine orders that were commonplace in early 2009 have been replaced by rapidly shrinking orders as the 2008 drop in project financing for developers filtered through to turbine manufacturers in the second half of 2009. Industry players have responded to this trend by reducing their exposure to the sector. For example, Iberdrola divested 10 percent of its holding in Gamesa for over €391.7m in a private placement in June 2009. Later in the year, AE Rotor received £224m for its 35 percent share in Hansen Transmissions, while United Technologies acquired a 49.5 percent stake in Clipper Windpower for £166m.

Government Incentives
The failure to achieve a global agreement on emissions targets at the UN Climate Change Conference in Copenhagen last November will not dent M&A activity in the renewables sector, according to 88 percent of the KPMG/VB Research survey respondents. In the absence of a standardized global structure, regional government incentives and initiatives will be employed to boost renewable investment. Significantly over half of the surveyed respondents predict that these regional regulations and tariffs will accelerate M&A activity during the next 18 months. The most prominent such incentive is the U.S. American Recovery and Reinvestment Act (ARRA), which came into effect in early 2009 and, combined with subsequent stimulus measures, has made North America the preferred geography for acquisitions of renewable energy projects or companies. Almost half of the European and a third of the Asia-Pacific respondents are considering acquisition targets in North America in the next 18 months.

However, the market is keenly aware that such government support is of limited size and duration, and that it must generate activity independent of these incentives. Cord Landsmann, CFO at E.ON Climate and Renewables GmbH, says, “We aim in the long run to achieve grid parity without subsidies… we would not choose locations with poor or uncertain access to the energy source, even though they could benefit from important incentive-based regimes.” Other drivers of cross-border M&A in the sector include energy security in the form of reliable energy supply and secure production facilities; volatile fossil fuel prices; market consolidation; and increasing demand within society for a renewable/alternative energy supply. M&A deals will also be boosted by financial backers looking to exit their current portfolio companies. Venture capital investors who reached their investment limit during the downturn by providing follow-on financing to their portfolio companies, and funds that were raised over five years ago are desperately looking to exit some of their investments. With the IPO market still fragile, M&A is the most attractive exit route.

Government incentives, coupled with more liquid capital markets, will ensure that both corporates and investors approach 2010 with a greater focus on M&A. According to VB/Research’s survey, more than 90 percent of respondents are considering M&A activity in the next 18 months, compared to an equivalent report from 2009 when 45 percent of the surveyed respondents were either not planning to make any acquisitions during the following 12 months or were undecided. Thirty-six percent of respondents said they are targeting acquisitions in the wind sector.

Bolstering Technology Capacity
Corporates will target acquisitions that increase generation capacity, leaving technology and equipment company acquisitions to investors. Landsmann says that “We follow our boutique to industrial approach and target projects based on scalable technologies that can provide synergies, and reduce costs. The wind sector is at an advanced stage of development and provides such characteristics, while the solar sector is the next to follow with a huge potential of scalability.”

As the most mature renewable energy sub-sector, synergistic technology acquisitions and downstream integration is less critical to corporates active in the wind sector. Financial investors are expected to be the major players in takeovers and investments in technology and equipment companies. Few of the surveyed corporates plan to acquire onshore wind technologies and equipment or onshore wind management and installation companies during the next 18 months, whereas investors are expected to be more active in these markets, driving efficiency savings through market consolidation.

“The onshore wind sector started its consolidation in 2002-2003, but there is still room for deals to be done. If further consolidation does not take place over the next 18 months some companies will disappear,” according to Anil Srivastava, CEO of Areva Renewables. Institutions such as pension funds and sovereign wealth funds will facilitate the access to finance for highly capital-intensive industries such as the offshore wind sector, where single projects can require in excess of €1 billion of capital expenditure.

Alongside these financial investors, the institutions that will be most active in the next 18 months are large corporates with strong balance sheets and an international presence, enabling them to pursue deals without needing to secure additional debt finance. An overwhelming majority of survey respondents (77 percent) expect specialist renewable energy companies and subsidiaries of integrated utilities to be the most active participants.

Access to Debt Markets
There is more good news for the wind sector thanks to an improvement in the disposition of debt providers. After a period during which the debt markets virtually ground to a halt, banks are now set to become slightly less risk-averse. A third of the surveyed debt providers indicated an intention to increase their exposure to the sector in the next 18 months. Onshore wind warms are viewed as the most risk-free proposition for these entities. Seventy-five percent of those surveyed stated that they were interested in financing onshore wind farm projects. However, debt financing will be harder to come by for wind technology companies: 25 percent of the surveyed debt providers said they would be interested in providing solutions to that sub-sector.

Debt financing should be easier to raise in 2010. However, the case for asset financing needs to be stronger than they may have been pre-2008. As Srivastava notes, “Prior to the crisis, renewable energy was an industry of announcements, announcements of projects that would not be feasible to build. Today contractors are required to have a real ability to execute and a large balance sheet.” Another symptom of the banks’ continued caution is that they are still not inclined to approve debt tenures beyond 15 years. Margins for debt financing have also risen considerably. An onshore wind project in Europe is now financed at an average rate of 300 basis points (bps) over the base rate, compared to 100 bps in 2007.

This means that equity financing remains critical to financing efforts in the renewable space. The survey indicates that North Americans are the most confident of tapping these markets, as 32 percent of respondents from the region indicated their confidence that they can access this form of financing. Although traditional financing sources are reopening, financing M&A transactions may not be straightforward. Acquirers in the sector may well need to continue to find creative financing arrangements to bring their renewable plans to life.  

With governments across the globe becoming ever more aware of the environmental benefits of wind-generated power, the number of wind farms and the financial investment in constructing, erecting, and maintaining wind turbines is increasing exponentially. Today the market is estimated to be worth $60 billion annually, with global wind capacity expected to double every three years. According to the World Wind Energy Association’s (WWEA) “World Wind Energy Report 2009” the United States is the world leader in terms of the installed capacity of wind power, followed by China, Germany, Spain, and India. WWEA figures show that last year these five countries together accounted for nearly 80 percent of worldwide wind capacity.

Such a high level of investment, coupled with the increased dependence on wind power, has led turbine manufacturers and operators to become acutely aware of the financial implications, safety issues, and environmental impact of fire-damaged or destroyed turbines. Indeed, fire safety has become such an issue that the United States’ National Fire Protection Association (NFPA), Germany’s Vertrauen durch Sicherheit (VdS), and Germanischer Lloyd have developed recommendations, standards, or codes of practice.

The NFPA has recently added wind turbine and outbuilding fire protection standards to NFPA 850, titled “Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations, 2010 Edition.” This document provides fire protection recommendations for the safety of construction and operating personnel, physical integrity of plant components, and the continuity of plant operations. The revised 2010 edition includes detailed recommendations relating to wind turbine generating facilities.

VdS 3523en (wind turbines, fire protection guideline) has also been used as the basis for the CFPA E, or Confederation of Fire Protection Associations in Europe, guideline no. 21.2010 F, which addresses the same topic. VdS is a highly-regarded, independent, international, third-party accreditation and certification body for fire prevention and safety technology. Germanischer Lloyd, which specializes in classifications for the maritime and energy industries, has developed Renewables Certification Guidelines: “GL Wind Technical Note Certification of Fire Protection Systems for Wind Turbines, Certification Procedures, Revision 2, Edition 2009.”

Scale of the Problem
A report by the AREPA Group—a technical service organization with operations throughout Europe that specializes in the assessment and restoration of damaged technical equipment—suggests that 184 wind turbine components were damaged by fire since 2002, while the Caithness Windfarm Information Forum believes that, as of September 2009, 122 wind farm fire incidents were reported globally. The cost of property damage on each of these reported incidents spans from $750,000 to $2 million. Figure 1

However, many in the industry believe that these figures grossly underestimate the scale of the problem. A significant number of turbine fires go unreported, possibly because of a combination of their remote location and the fact that the emergency services are not always called upon to attend, and these fires do not form part of any official fire incident statistic.

Turbine Fire Risk
The almost inevitable consequence of these industry initiatives has been that a number of detection and suppression systems have been put forward as suitable solutions. While many are effective for what might be regarded as “conventional” applications, they may not be suitable for the particular fire challenges found in wind turbines.

The majority of turbine fires are started by a lightning strike, brought about by their exposed and often high-altitude location and the height of the structure; turbines are now being built that are up to 320 feet high. Mechanical failure or electrical malfunction also account for a significant percentage of fires that can be fuelled by up to 200 gallons of hydraulic fluid and lubricants in the nacelle, which itself is constructed from highly-flammable resin and glass fiber. Internal insulation in the nacelle, which can become contaminated by oil deposits, add to the fuel load.

Electrical equipment is another high-risk area. Capacitors, transformers, generators, electrical controls, and transmission equipment all have the potential to catch fire, as do Supervisory Control and Data Acquisition (SCADA) systems. There is also the risk of fire due to loose or broken electrical connections or the overloading of electrical circuits. Figure 2

Braking systems pose a particularly high fire risk. Overheating can cause hot fragments of the disc brake material to break off, rupturing hydraulic hoses and resulting in highly combustible hydraulic fluid being expelled under pressure and coming into contact with the hot disk brake fragments. Hydraulic pumps and connections have also been known to fail, allowing the fluid to erupt into flames when it comes into contact with a hot surface.

Unique Fire Protection Challenge
What are the special challenges that an effective fire detection and suppression system for a wind turbine have to overcome? The core issue, of course, is remoteness. This is particularly the case with offshore wind farms, but even onshore farms are routinely in difficult to access or isolated locations. The essential characteristics of an effective wind turbine fire detection and suppression system are that it should:

• Deliver around the clock reliability and 24/7 unsupervised protection;
• Ensure an absence of false alarms;
• Contend with vibration, dust, debris, and airflow through the nacelle;
• Contend with extreme temperature variations;
• Stop a fire precisely where it breaks out, and before it takes hold;
• Require no external power.

The options that are often considered can be generally categorized as air sampling detection; water mist suppression; compressed-air foam suppression; fusible link detection and suppression; total flooding CO2 (carbon dioxide)suppression; total flooding clean agent suppression; and linear pneumatic detection and suppression.

Air sampling aims to offer early detection by collecting minute smoke particulates in the early stage of fire, but they do require a power source and control panel, which means that the system will fail if the external power or battery backup fails. These systems are also expensive, in part because they only detect a fire, and so need to be integrated with a suppression system.

The major drawback to air sampling in wind turbines, though, is the ever-present risk of false alarms. These can be caused by tiny particles of dust and debris and atmospheric pollution that are propelled around the nacelle due to the turbine housing having a number of openings to allow air to circulate to reduce the internal temperature. While false alarms are the bane of any system owner’s life, a false alarm in a wind turbine inevitably involves extensive travel and possibly the hiring of expensive specialist access equipment.

Suppression-Only Systems
Water mist suppression systems convert water into a fine atomized mist, but they too have limitations when used to protect wind turbines. Due to the turbine’s remote location and the distance from the ground to the nacelle, water mist systems are often impractical, plus they call for considerable space to be devoted to water storage, which increases the weight in the nacelle. These systems are also a costly part-solution to the problem, as they need to be linked to a detection system.

Water mist systems are total flooding solutions, which increase the potential for damage to electrical components and possible corrosion. Also, because in some locations the temperature can fall below freezing point, antifreeze has to be added to the water, and antifreeze is a combustible liquid that is itself a corrosive substance. Figure 3

Compressed air foam systems work on the principle that compressed air is injected into a foam solution to achieve a quicker fire knockdown when compared with conventional foam systems. While they need less water than conventional systems, the storage, weight, and freeze-protection problems are similar to those of water mist systems. In addition, these systems require considerable extra space for the operating components. After discharge cleanup can be extensive and, like water mist systems, the cost is increased by the need for a separate detection system.

Fusible link systems, however, do combine detection and suppression into one package and work on the basis that heat from a fire will rupture a fusible link—the detection element—that in turn will initiate the discharge of the suppressant. The challenge with these systems is that airflow in the nacelle can seriously impair performance and reliability because heat and flame that typically rise from the source of a fire may be propelled away from the location of the fusible link, critically delaying activation.

Total Flooding Gaseous Systems
Whether using CO2 or the latest clean gaseous agents, traditional total flooding suppression systems are designed to fill the entire space being protected with suppressant. While an established suppression agent, CO2 is not without its drawbacks. It is unsuitable for total flooding applications in potentially occupied enclosures, as its discharge in fire extinguishing concentrations would be lethal to occupants. Flooded areas must be adequately ventilated after discharge to prevent accidental exposure of personnel to dangerous levels of CO2 when investigating the cause of a discharge.

These challenges do not exist with clean agents, however, such as 3M™ Novec™ 1230 fire protection fluid. The suppressant is stored as a low vapor-pressure fluid that, when discharged, vaporizes into a colorless and odorless gas. Typical total flooding applications use a concentration of the fluid that is well below the agent’s saturation or condensation level, and its low design concentration means that less space has to be devoted to cylinder storage. Novec 1230 has a negligible impact on the environment, with insignificant global warming potential, zero ozone depletion, and an atmospheric lifetime of just five days. Once discharged it leaves nothing behind to damage sensitive electronic equipment.

Traditional total flooding systems are not without any downsides. Vibration can loosen connections while dirt, dust, and temperature extremes are known to cause unwarranted discharge. Additionally, openings in the turbine housing significantly inhibit achieving the designated agent concenwration. Devising a solution to overcome these challenges can add significantly to the weight in the turbine.

Integrated Detection and Suppression
The major drawbacks of traditional total flooding suppression systems, and the shortcomings of other technologies put forward for the protection of wind turbines, are overcome in the Firetrace® linear pneumatic system that provides both fire detection and suppression in a single package. It is a self-contained system that, significantly, requires neither electricity nor external power; a solution that is activated automatically around the clock without the need for manual activation or monitoring, and it requires virtually no maintenance. It is an intrinsically safe solution as it does not contain any components that produce sparks, or that can hold enough energy to produce a spark of sufficient energy to cause an ignition.

Firetrace is comprised of a cylinder that for wind turbine applications contains 3M Novec 1230 and is attached to a purpose-designed proprietary Firetrace detection tubing via a custom-engineered valve. This leak-resistant polymer tubing is a linear pneumatic heat and flame detector that is designed to deliver the desired temperature-sensitive detection and delivery characteristics. It is routed throughout the areas to be protected and, when the tubing is exposed to heat and radiant energy from a fire, it ruptures and instantly directs the suppression agent at the source of the fire.

With over 150,000 Firetrace systems installed around the world, a key factor in its success is the system’s reliability. The fact is that the only thing that will rupture the tube is heat or flame from a fire, so there is no prospect of false alarms. Yet if a fire breaks out, the response is unerringly immediate and accurately targeted. It is the only Underwriters Laboratories (UL) listed, Factory Mutual (FM) approved, and Conformité Européene or European Conformity (CE) marked tube-operated system in the world that is tested as an automatic fire detection and suppression system.  

Wind gearbox technology is developing at a fast pace, not least due to operators demanding ever more power and efficiency. Experience has shown that the lubricant used is a crucial factor in meeting the wish for ever-increasing performance. Besides strictly technical requirements, aspects of economy and ecology are receiving more and more attention in lubricant selection.

The technical requirements to be met by a lubricant are defined either by the gear manufacturer, by pertinent standards, or the operating conditions. Among the “classic” requirements are a specific nominal viscosity, viscosity index, service temperature range, and minimum scuffing load capacity, as well as compatibility with the elastomers that are used for radial seals. In heavily loaded spur gears, sufficient micropitting resistance and good antiwear characteristics of the gear oil used are today also considered important. What machine operators basically expect from a special lubricant is cost reduction. This is attained by long oil life, simple oil change, wear-free or near-wear-free operation, and high efficiency in all lube points. Consequently, these are the factors that are foremost taken into account for the development of new gear oils by Klüber Lubrication.

Base Oils Determine Technical Performance
The first important decision is the careful selection of suitable base oils. Synthetic base oils are often chosen since their characteristics can have a very positive effect on the gear oil to be created.

Table 1 compares a number of typical base oil characteristics. The more suitable the base oil is, the less will additivation or other adjustments become necessary at a later stage to attain the desired properties. An example of such adjustments is the addition of so-called viscosity-index-improvers, which can substantially enhance the viscosity-temperature behavior of mineral oils. On the other hand, the chemical makeup of such polymer additives may lead to the breaking of molecular chains under the shear rates commonly found in gear contacts (approx. 10-6 1/s), which counteracts the desired effect of a higher viscosity at elevated temperature. This problem is prevented if oils with a higher viscosity index are used in the first place.

Lower Friction Improves Efficiency
Figure 1 shows the friction coefficients of several base oils measured on a two-disk test rig. This test rig allows friction coefficients to be determined under conditions as prevail in gears. It can be seen that the polyglycol-based gear oil Klübersynth GH 6-150 in particular leads to significant friction reduction. Depending on the type of gears lubricated, this may bring about considerably better gear efficiency. The positive effects of a higher efficiency are manifold. One is lower energy consumption at constant output power. Lower oil temperature and hence longer oil life is another. Obviously, this leads to a reduced oil consumption, but also to savings in terms of time and money to be spent on oil change.

These benefits have been proven in tests conducted on Klüber’s worm gear test rig, as shown in Figure 2. Figure 3 shows some exemplary results for Klüber gear oils. When the polyglycol oils are used in heavily loaded worm gears, temperature reductions by more than 40 °C and energy savings of 30 percent are realistic. Whether the oils tested were gear oils for general applications (Klübersynth GH 6 series) or special oils for the food-processing and pharmaceutical industries (Klüberoil 4 UH 1 N series, Klübersynth UH1 6 series) had no effect on these results. The latter can generally be expected to offer the same if not better performance than conventional gear oils. Oils based on polyalfaolefins, e.g. Klüberoil 4 UH1-460 N, do not perform quite as good as polyglycol oils, however they still offer significant advantages over mineral oils. Such polyalfaolefin-based oils might be recommended for use in old gears where compatibility with paints and seals of unknown origin are a particular priority. Polyalfaolefins can also be mixed with mineral oils. What should be noted, though, is that conversion to a food-grade oil always requires thorough cleaning of the machinery since an undefined mixture of old and fresh oil will fail to satisfy food safety requirements.

Additives are particularly important under conditions where no separating lubricant film can form. Such conditions are found, for instance, during the running-in of gears, or in gears driving low-speed machines as well as in stop-and-go operation.

Wear Protection for Longer Service Life
Figure 4 shows the differences in wear behavior attained with different oils in worm gears. The results shown were again obtained in tests on the Klüber worm gear test rig. The left axis of the diagram represents the weight loss of the worm wheel after the test, while on the right the wear rate of the wheel is shown. Seen in combination, the results allow a differentiation between running-in wear and permanent wear. Under the selected operating conditions it can be assumed for the mineral oil that wear on the worm gear will decrease tooth thickness at a rate of approx. 1/1000mm per hour. With the Klübersynth GH 6-460 oil, on the other hand, there will be only minimal tooth wear. It is obvious that the particular characteristics of this oil cause pronounced running-wear on the gear; however, the permanent wear setting in after a certain time is very low. Naturally, the life of both the gears and the gear oil benefit from these characteristics. If wear on the worm gear is eliminated or kept to a minimum, the replacement of parts or even the whole gear system can be avoided. At the same time less wear particles contaminate the gear oil, which means the latter can be used longer, irrespective of the base oil characteristics.

An oil’s service life is primarily determined by certain factors and by the way they interact, which is shown in Figure 5. In this figure, oil sump temperature is indicated as a function of oil service life. The slope of the curves is due to the so-called 10 K rule, saying that a temperature increase of 10 Kelvin doubles the speed at which chemical reactions take place. Applied to the service life of gear oils, this means that their life is cut by half with every 10 K temperature increase. The curves for mineral oil and polyglycol have been taken from the literature, where they have been published on many occasions. Klüber Lubrication drew on their practical experience in the use of polyglycol oils by performing numerous used-oil analyses with this oil type and evaluating them. Some of them are shown as symbols in the diagram. All results stem from applications where there was clearly no gear damage due to the gear oil being past its service life. The results of this evaluation show that the selection of the right base oil can contribute decisively to attaining a longer service life. A polyglycol oil used in a gearbox application can last five times longer than a mineral oil. This is without taking into account that if, for example, a Klübersynth GH 6-460 oil is used, the operating temperature will go down considerably and the amount of wear particles be reduced, which will additionally extend the oil’s lifetime.

The fact that the oils discussed can be used both in spur gears and in worm gears greatly facilitates maintenance in that it allows a streamlined product range. Fewer oils are kept on stock, which helps to avoid confusion. Hence, the consistent use of synthetic gear oils leads to significant cost savings for the operator, which may justify the higher purchasing costs for synthetic oils compared with those of mineral oils. It makes therefore sense to choose a more global approach to cost considerations, and in particular to include maintenance and repair.