What to do about rising rare-earth prices
October 18, 2011 by Paul Dvorak
Filed under Materials, Wind Power Generators, Wind Power News
Panu Kurronen, Product Manager, The Switch
By Panu Kurronen, Product Manager, The Switch
The growing global demand of rare earth metals combined with China’s ever-tightening grip on the material keep pushing up magnet prices. While we at The Switch don’t think the price trend can last too long, we understand that the matter is of great concern for the wind power industry. To tackle with this alarming situation and to meet future needs, the industry needs to change its perspective to open new opportunities.
The Switch has done intense research and development to reduce the amount of magnets needed for the production of p
ermanent magnet generators (PMG). Based on the successful testing 20 different generators, we are in a position to make a third generation, permanent-magnet generator. Combining field experience with state-of-the-art design methods has provided the skills to produce classical machines and innovation to the PMG field.
First, in most PMG designs, the risk of demagnetization of the rotor has been eliminated to the greatest possible degree by using high-dysprosium content rare earth magnets. Dysprosium is the most critical element in the magnet. However, many worst case scenarios related to a PMG design are exaggerated fears, and the demagnetization risk can be safely eliminated even when using lower grade magnets.
Another way to optimize costs is to design effective cooling for the generator. The lower the magnet temperature, the cheaper the selected magnet grade can be. Magnets with a higher temperature class, such as those with dysprosium, are more expensive. Still, more power can also be generated with lower temperature coolant. Even the machine size can be reduced to generate the same output power.We continue to believe that PMG technology in different configurations offers a viable alternative for future turbines. A direct-drive PMG concept with a simple mechanical construction and high efficiency levels well highly suited for offshore turbines. However, the machine’s large physical size often requires large amounts of magnets for the production.
The Switch high-speed PMGs feature a three-stage gearbox. Based on the machine concept and operating range, the magnets once used higher-grade material, and so required higher amounts of dysprosium. The magnets are embedded inside the rotor for increased mechanical strength.
A multi-megawatt medium-speed PMG, such as The FusionDrive requires a fraction of the amount of magnets needed for direct-drive generators with an equal power rating. The FusionDrive power train combines a gearbox, traditionally the largest component in a turbine, and a PMG in a way that produces a smaller and lighter drivetrain than possible by other methods.
The Switch
www.theswitch.com
Entrepreneur Proposes Wind-Turbine Gear Factory For Indiana
September 12, 2011 by Windpower Engineering
Filed under Turbine Design, Wind Turbine Gearboxes
You might think the U.S. has lots of gear-making capacity, so why would a start-up envision a factory capable of more of the same? The answer lies in the size of the gears planned by Vela Gear Systems CEO Noel Davis. Gears required in the wind industry can be in excess of 6 ft in diameter, while gearboxes weigh up to 20 tons. In addition, the nation has more than 30,000 utility grade wind turbines, where every year more approach the end of their warrantees and some near retirement. This means many may need gearbox repairs or replacements.
Davis and his colleagues are well acquainted with wind turbine gearboxes. He ticks off the types that will need repair and possibly replacement: “A planetary gearbox for a typical 200-ft high 1.5-MW wind turbine weighs more than 15 tons. Its sun gear has about a 24-in. diameter and 5-ft length, three planet gears each with about a 30-in. diameter. The ring gear has about a 70-in. diameter while spur or helical gear easily have 40-in. diameters. The output pinion driving the generator can weigh a hundred pounds. There are also smaller gear drives that pitch the three blades to catch the wind, and azimuth drives to rotate the entire 100-ton nacelle to face the wind.” None of these large slewing rings and gearboxes are small enough to be handled at the more frequently encountered automotive gear facilities.”
What’s more, says Davis, main-drive gearboxes have individual components that may weigh up to 10,000 lb, and when assembled, 20 tons. These components cannot be lifted by hand and require lifting equipment and an overhead clearance beyond what is available in most automotive-component facilities. Lifting large components, such as 6-ft diameter gears in and out of machine tools, then assembling them into a 20-ton gearbox, and then onto a flatbed truck for transport, requires a taller gantry cranes than those at most facilities. And the next generation wind turbines are just getting bigger. In the end, Davis sees a purpose-built facility just for wind-turbine gears.
Noel Davis
But where to build? Davis starts sketching a Venn diagram with three circles in North America: the location of wind farms, the location of raw material, and the location of the skilled labor. “Wind farms are mostly in the middle of the Midwest. Steel comes mostly from the areas spanning Milwaukee to Pittsburgh, and skilled machinists needed for this business are found in automotive manufacturing states. These three circles intersectd in Indiana, an ideal location for this business,” he says. Marion, Indiana to be specific.
Davis also has ideas for financing this ambitious venture. “I have some money from the sale of a previous company that I have put up. The Chamber of Commerce for Marion has also secured a hundred million dollars in bonds. But those convert only if we can drum up enough business to fund the debt of the bonds.”
He figures that his skilled workers will earn $23 per hour with a fully burdened rate of $40 per hour, while Europeans are importing this product at $60 per hour plus ad extra 15% of the total cost for ocean freight and logistics to North American wind farms from European manufacturing sites. Bottom line is that a promise from OEMs to build about 20 gearboxes each year will be the minimum needed to secure the bonds. Soon after that, Davis sees groundbreaking on the new factory, laying the foundation, ordering the machine tools, and hiring the staff.
Washington is fond of patting itself on the back for its gutsy calls, that in hindsight, are not terribly difficult. Building a new factory in American is the real gutsy call.
WPE
How are gears & gearboxes used in wind turbines?
May 18, 2011 by Windpower Engineering
Filed under Mechanical Components, Wind Basics
Gears and gear manufacturing: Uncontrollable and highly variable wind forces adversely affect the performance and reliability of planetary gears inside wind-turbine power transmissions. A couple developments can lower maintenance on rolling elements and carry greater load in a planetary gearset. The first idea is to equalize gear loads, reducing internal stresses and significantly extending wind turbine reliability. The load sharing idea can be used in open planetary gear sets and consists of a double-cantilevered pin supporting the bearing and gear. The cantilevered pin attaches to a single carrier wall, and a cantilevered sleeve mounts to the free end of the pin. Gears and bearings mount on the sleeve.
Two opposing arrays of these bearings mounted on a double-wall planetary carrier let the drive carry up to 50% more torque. Furthermore, the integrated bearing and gear construction is simplified to provide more space for rolling elements to maximize the power rating of the bearing system. For max durability, coatings may be applied to the rolling and sliding surfaces. The result: More evenly distributed torque among multiple planet gears and longer gear and bearing life. In addition, combining shafts, bearings, and gears in one unit also cuts weight and lowers cost.
Conventional turbine design uses a gearbox to speed the slow, but high-torque power in a main shaft to a higher rotational speed useful to the generator. Conventional utility-scale wind turbines often use three- stage gearboxes. The first stage is often a planetary drive because that design handles high torque best. The later two stages use helical gears.
To give an idea of the torque coming from a rotor, consider a 1.5-MW turbine working at its rated output. 1.5 MW = 2,011 hp.
Using the torque and speed relationship, assume about 15 rpm on the rotor. Using,
Php = ωT / 5,252 Where Php = power, (horsepower); ω = rotational speed, (rpm); T = torque, (lb-ft); and 5,252 is a conversion factor.
Solving for torque gives:
T = 5,252 Php/ ω
= 5,252 (2,011 hp) / 15 rpm
= 7.04 x 105 or about 700,000 ft-lb
That is, 700,000 ft-lb on the gearbox input shaft. Of course, a 1.5-MW turbine works at this full load only a small part of the time.
The calculation may prompt the question: What are the loads on a gearbox? Instead of a few figures, gearbox designers work with load cases, loads measured by sensors on working gearboxes over a period of time. That means loads are constantly changing. Also consider that equipment encounters the changing loads on a tall tower swaying in the wind and exposed to temperature extremes. Eventually, a rotor shaft and gearbox lose their alignment. That creates additional loads on the gearbox and bearings. The same happens between gearbox and generator. These conditions result in frequent gearbox failures and a reputation for unreliability. When a gearbox fails, the turbine must be taken off line (out of power production) while the gearbox is replaced, an expensive task that can take several weeks.
Shaft couplings: Flexible shaft couplings accommodate that slight misalignment between gearbox output shaft and generator shaft. Several designs have found favor. One steel-shaft coupling rated for up to 9,200 ft-lb is said to be free from wear and maintenance, work quietly, provide electrical insulation, and is torsionally soft and flexible in all directions.
Another design uses two sets of links, one on each end of a tube to form a double cardanic system. The links connect through rubber bushings. The manufacturer says it can be sized for any torque, needs no maintenance, its electrically insulated, damps noise and vibration, and is flexible in axial, angular, and radial directions.
More recent designs use a fiberglass composite membrane and fiberglass tube. Membranes at each end of the tube provide sufficient axial and angular flexibility. It’s rated for torques up to 14,750 ft-lb., has a low weight, and is maintenance free, electrically insulated, and torsionally stiff.
Trends in gearboxes
May 14, 2011 by Windpower Engineering
Filed under Editorial, Mechanical Components, Turbine Design, Wind Turbine Gearboxes
Despite the recent surge in wind-turbine announcements regarding direct drives, gearboxes are not going anywhere. They will remain a necessary component in many turbines, and so are pushing trends in several directions—toward lighter overall turbine weight, improved durability, and design for maintenance.
“After ten years of research and study, we know why early gearboxes did not stand up well to the duty hazards in wind turbines,” says Timken’s Hans Landis, Director, Process Industries OE & Wind Energy. “And those lessons have been disseminated throughout the gear industry.” The lessons start with a better understanding of the loads on a wind turbine gearbox. For instance, the constant pounding of the wind on a rotor and main shaft of older designs could slowly hammer away at the gearbox. Higher loads would slowly damage bearings, then gears, and eventually require a gearbox swap. More recent designs let better bearings handle loads so gearboxes need not.
Early main-shaft gearboxes on kilowatt-sized machines were off-the-shelf industrial units with minor modifications. The obvious gearbox trend is that they have gotten bigger with megawatt outputs, and each is designed for its turbine model. “There are no off-the-shelf designs today,” says Mike Carlson with Hanson Transmissions. “Each is designed for the turbine platform and in collaboration with the OEM. Inside, the slow, high-torque rotor speed is initially stepped up with a planetary stage followed by two more stages. Generally below 3 MW, the second or intermediate stage uses helical gears. But 3-MW and larger turbines need a planetary design in the second stage and a helical stage for the high-speed output.” And if OEMs continue designing larger turbines, that last stage will also use a planetary design.
Somewhat easier maintenance has also gotten attention, says Carlson. “Although not all maintenance will be possible in a crampt nacelle, more than what was previously possible will be.”
Romax, a developer of software for gearbox simulations, sees a trend of integrating the bearings that support the main shaft and rotor into the gearbox itself. This can have significant advantages and reduce overall drivetrain size. It also allows reducing gearbox stresses due to high rotor loads.
The market is seeing more integration between gearboxes and generators. This has advantages in terms of overall size, weight, and cost. In some cases, the number of bearings can be reduced in the drivetrain, and the gearbox consists of just one or two planetary gear stages with no high-speed shaft.
Several years ago, a study released by NREL showed that a combination medium-speed gearbox and PM generator would provide the lightest weight drivetrain. That may have encouraged turbine manufacturers to consider medium-speed drivetrains for large wind turbines–typically for machines of 3 MW and above. Medium-speed drivetrains use larger, more costly generators that run at lower speed but with the advantage of reducing the cost and complexity of the gearbox. Fewer gears and bearings are involved in the design – medium speed gearboxes typically consist of one or two planetary gear stages and have ratios between 1:7 and 1:35.
Moventas, a manufacturer of gears and gearboxes for wind turbines, and The Switch, a supplier of megawatt-sized permanent magnet generators and converters, now offer one to the industry. “The lower the nacelle weight, the more cost competitive the turbine,” says Moventas CEO & President Jukka Jäämaa. “Nacelle weight relates directly to foundation and construction costs of the turbine, as well as manufacturing, transport, and assembly costs in the whole supply chain.”
WPE
Portland wind gear assembly kicks off
March 21, 2011 by Kathleen Zipp
Filed under Mechanical Components, Wind Turbine Gearboxes
- Moventas will assemble gears for the U.S. wind industry at its new plant in Portland, Oregon.
Wind gear manufacturer Moventas kicked off its USA assembly operations by expanding its existing facilities in Portland, Oregon. As of February, domestically assembled wind gearboxes are available from Moventas in North America. Initial capacity will be 200 MW, while the company continues to build even larger capacity in the Midwest area.
General Manager Steve Casey is currently training Portland staff. The first wind gears made in the USA will be 1.5 MW, and later assembly will also cover the 2-MW class. Initially, units will contain imported parts, but the company will gradually incorporate the local supplier network, according to Moventas Senior Vice President of Group operations, Ahti Ahonen, who is overseeing and supporting the project.
Moventas www.moventas.com
Re-building a better gearbox
February 28, 2011 by Paul Dvorak
Filed under Maintenance, Wind Power News, Wind Turbine Gearboxes
Broadwind's modular test rig is capable of full-load testing up to 3 MW.
As OEMs build larger wind turbines, they push the bounds of what’s possible for a 20-year service life. Occasionally, the boundaries push back with failures, often of gearboxes. Technicians at Broadwind Services, a division of Broadwind Energy in Abilene, Texas, say they can fix those broken gearboxes and make them better than new in a recently opened a 60,000 ft2 facility.
The facility will disassemble, remanufacture, and do full-load testing on large wind turbine gearboxes. “We made upgrades to the overhead cranes, tooling, and equipment for the work cells that will do disassembly and reassembly,” says President of Broadwind Services Paul Seppanen. “An impressive test bench allows full-load testing up to 3 MW. It’s modular so it can handle the full range of gearboxes that are installed in turbines,” he says. Gears that need regrinding and replacement will be shipped to Broadwind’s gearing facility in Chicago.
Broadwind's Seppanan says worn gearboxes can be remanufactured to better than new conditions.
The company says its plan is to put back a better gearbox than it took out. “We can figure out why it failed, and look for the next revision of bearings, for instance, because those manufacturers are constantly innovating as well. Also, wind-gearbox OEMs are making multiple versions of their boxes, sometimes they have a model number that ends in -3 or -4. We can remanufacture an early gearbox version, upgrading it to a later specification, or even beyond the specification of the most recent version of the box. “Proprietary techniques such as superfinishing the gears so they mesh better, improved lubrication equipment, and a range of other enhancements will extend the life of the gearbox,” he says.
Seppanen says root-cause analysis is a core competency at the facility. The company has been inspecting and remanufacturing gearboxes for eight years in the U.S., mostly on the kW scale. “That experience will be put into MW gearboxes,” he adds
Some failures are caused by manufacturing defects, some come from loads and fatigue over the design life, and a small number just fail early. “Many wind turbines have stretched the limits of their gearboxes and in some cases loads they see are beyond what they were designed for. Originally, gearboxes in smaller turbines would run smoothly without substantial failure frequency over their working life.”
Analysis starts in the field often before a gearbox completely fails. Teams will be up-tower with borescopes looking inside the gearbox and using condition or vibration monitoring equipment to diagnose what might be going wrong. That data goes back to the shop for the team that will tear it down. Then working back through a chain of events lets the repair team understand the root cause. We might find damages to a gear or shaft but we know that what really led to that was the bearing that failed early. Experienced engineers will make the analysis. Remanufacturing the gearbox will solve the root-cause problem so when the gearbox goes back to the field it will run longer on its second life.”
Some owners carry a pool of swap boxes. “Part of the company strategy is to also build a pool of spare boxes. When an owner with a turbine down contacts us for one, we’ll sell the spare box to the owner and buy back the damaged “core” in exchange. In the ideal mode, the truck that takes out the remanufactured box hauls back the damaged unit,” he says.
Gearbox lube for wind turbines
August 10, 2010 by KRemington
Filed under Lubricants, Wind Power News, Wind Turbine Gearboxes
One way to improve wind-turbine efficiency is with proper gearbox lubricant. Dow recently introduced the UCON GL-320 lubricant for wind turbine gearboxes and those in other applications. The high viscosity index of the lube, addresses the issue of cold weather causing high lubricant viscosity without the need for additional VI improvers. It has higher heat capacity than hydrocarbon oils, which allows it to move more heat, forestalling a shutdown when turbine output is at the maximum. The lubricant has better lubricity at ambient conditions, so it has potential to shift the power-versus-wind-speed curve to the left, leading to greater power output when the production is less than the maximum design output.
This lubricant also addresses the issue of micropitting, which can lead to wearing and changes in gear teeth shape, reducing gear accuracy, and increasing vibrations and noise. It can also lead to other problems such as misalignment and fatigue failure. High viscosity lubricants like UCON GL-320 are a thicker lubricant film that can help to reduce the debris and worn particles that often accompany less well-lubricated gears.
DOW
Large part machine shop ready for turbines
August 3, 2010 by KRemington
Filed under Mechanical Components, Wind Power News, Wind Turbine Gearboxes
After years of supplying the plastics machinery business and other companies in the industry, Milacron Machining, Mt. Orab, Ohio, is now applying its precision machining expertise to produce large, complex parts for the wind power market. “We have machined components for 2.5 MW and 1.5-MW gearboxes including housings, and planetary carriers,” says plant manager Jim Kinzie. “The process requires component machining, assembly, and line boring to complete an assembly. The physical sizes of the gearbox and carrier components have ranged from 4-ft cubes to one 12 ft on a side. Other components such as retainers, bushings, and pins have been manufactured or procured.”
Jim Kinzie and crew pose in front of a gearbox housing that will hold several generators for a 2.5 MW turbine. Huge horizontal milling machines and his skilled team produced the part.
The company facility features a ISO 9001:2000 and 14001:2004 certified manufacturing environment, complete with specialized equipment to machine tight-tolerance and large parts up to 150,000 lb. The plant includes climate-conditioned as well as secondary metalworking areas, all staffed by skilled employees who average 23 years of experience in the industry.
“We’re seeing a shortage of specialty machining providers in the wind energy market,” says Dave Lawrence, President of Milacron Worldwide Plastics. “To support these needs, we’re investing in our machining business.”
The company says it can handle large parts as well as small to medium lots of custom, design-driven components. In addition, a variety of job and industry-specific certifications let the company meet most manufacturing requirements. WPE
Gearbox manufacturer opens wind-turbine service center at Vernon Hills, Ill.
June 8, 2010 by Paul Dvorak
Filed under Maintenance, Wind Power News, Wind Turbine Gearboxes
ZF Services, the aftermarket business unit of ZF Friedrichshafen AG, now offers wind turbine gearbox services out of its Vernon Hills, Ill. remanufacturing and parts distribution center. With the addition of the Vernon Hills, Ill. facility, the company now operates six wind turbine gearbox service centers around the world, with the Dortmund, Germany service center being in operation for over three years.
For owners of wind farms in international markets, ZF Services can provide one point of contact, eliminating the need to source qualified gearbox service partners in each region. The company’s international presence offers further benefits to all wind farm owners through:
- A global inventory of swing units, bearings and other spare parts
- Reduced pricing of commodity parts as a result of the company’s purchasing power
- Increased knowledge of wind turbine gearbox-specific problems due to international experience with more gearbox types and sizes
Equipped with a 30-ton capacity crane and veteran gear specialists, the company is centrally located within the region and can perform complete repair of the gearbox and main shaft, update units to the latest engineering specifications, upgrade lubrication systems and perform engineering upgrades that eliminate repetitive failures.
In addition to gearbox repair, ZF offers a full range of up-tower services. These include end-of-warranty validation of gearboxes with endoscopic gearbox inspections and minor repairs to the gearbox while in the nacelle.
Dow lubricant brochure for wind turbine gearboxes
June 2, 2010 by Kathleen Zipp
Filed under Lubricants, Uncategorized
The Dow UCON™ GL-320 lubricant was developed for wind turbines, though it can also be used for other types of gearboxes.
Turbines can shut down in cold weather because of filter failures resulting from high lubricant viscosity. UCON™ GL-320 has a higher viscosity index to address this issue without needing additional VI improvers. The lubricant also has a higher heat capacity than hydrocarbon oils, which allows it to move more heat, reducing shutdowns. It’s polyalkylene glycol based and has the potential to shift the power vs. wind speed curve to the left, resulting in greater power output.
The brochure is available for download at www.ucon.com.
The Dow Chemical Company
dow.com
