Major Transmission Project Planned for the Atlantic Coast

Trends in utility scale wind turbines

If money were less of an object, developers would always put the largest turbines on the tallest towers possible. That would ensure the highest possible capacity factors from about 5-MW units and give a significant boost to power production. It would also, however, be costly. To find the right mix of turbines for the wide range of U.S. climates, turbine OEMs have responded with many focused designs. For example:

Onshore work is likely to fall to 1.5 to 3-MW turbines. In fact, 1.5-MW units seem to be a sweet spot. GE Energy, for example, recently installed its 15,000th, 1.5-MW turbine at Crow Lake wind farm in South Dakota. The feat is testament to the manufacturing idea that if you make enough of something you can drive costs down and quality up. Community-owned wind farms located on islands seem to like the 1.5 to 2-MW units from several manufacturers.

Direct drives may be another trend if neodymium, a material ideal for high-flux-density magnets, says relatively inexpensive. The material recently hit about $140/lb, up from about $70/lb a year ago. Should Chinese sources decide to withhold the material from world markets for internal use, prices will climb further. Then it will be necessary to develop new sources. However, creative electrical engineers have already suggested there are ways to build efficient generators without the material, or less of it.

Low wind speed turbines: This may be the dominant trend. Marketing directors have recognized that there are a lot of moderate wind sites around the globe. Why not a turbine for them? Such units would allow placing turbines closer to loads–cities. Nordex Windpower is just one of several OEMs responding with its N117/2400, a turbine with a 2.4-MW capacity and a relatively large 117-m diameter rotor. The company also plans to mount this unit on a relatively tall 90-m tower.
Craig Christensen, Senior VP of Engineering for Clipper Windpower, says the 105-m rotor on the company’s previous C99 (99-m rotor turbine) will let the machine capture Class III winds with an improved capacity of about 35% (a 30% capacity factor is common) and in Class II winds capacity factors can improve to 40 to 45%. “The effort will require strengthening components all along the drivetrain,” says Christensen. “There’s more to it than a rotor swap.” Electric systems will change least.

The incremental refinements will also allow more reliable working periods after the warranty expires, often a 2 to 5-year period. All turbine manufacturers say they are working on reliability improvements. Christensen says about half his engineering team is working on them. For most turbines, the changes will lower operating costs. Upgrades will span all through the machine, from pitch to hydraulics to yaw and to the gearbox. Suzlon, GE, and Gamesa also have large-rotor units intended for lesser wind regions. Expect larger rotors and taller towers to go together. In the U.S., the 80-m tower is about standard but another 20m will make best use of the larger rotors. In Europe, the 100-m tower is standard.

Christensen identifies another emerging trend: Improved logistics that get components to sites more efficiently. Trucks are about at their load limits so modular designs will be appearing. “That may mean more trucks for a shipment but the components they carry will be more easily handled. Even now, he says, the Liberty 2.5 has been shipping the gearbox and generators separately and assembling them on site.

Upgrades and up-ratings are also the order of the day. It costs millions to develop a new turbine so it makes sense to push existing designs as far as reasonably possible, say from a 1.5 to 2.5, and then to 2.75-MW design.

GE recently commissioned its first 2.75-103 wind turbine at the Energy Research Center in the Netherlands. The new turbine features electrical system uprates and the company’s 50.2-m proprietary blade that it says boosts annual energy production by more than 9% at 7.5 m/s over its 2.5-100 machine.

Larger units: There was a time when 1.5 MW was a large turbine. Today it’s on the small end of the spectrum, as new turbines seem in the 2 to 3-MW range. For instance, Northern Windpower recently announced a manufacturing site for its 2.3-MW direct-drive turbine in Michigan.
Offshore work will fall to the larger units, most from 3.5 to 5 MW. Offshore will likely see large units because of the great effort of working at sea. One 5-MW unit uses a PM generator and a single stage gearbox. Also Vestas recent announced a 7-MW offshore turbine.

WPE

Trend in towers

Towers for wind turbines have done a good a job hiding their high-tech origins. For instance, their sections–humbly called cans–are rolled from flat-sheet steel into precise, yet slightly tapered cones and then welded by CNC machines. More CNC machine tools drill holes and attach flanges that allow connecting cans. But for all their sophistication the enclosed steel tower may have reached its limit. The trends are toward taller towers, hybrid designs, and modularity.

Towers are also getting attention because the tower-cost portion of the overall wind turbine is increasing from 10% toward 20% of system cost. More attention is on cutting transportation costs and reducing weight. Higher steel prices were an issue over the last several years, although it is lessening now.

Most new towers in the U.S. are 80m, and soon 100m will be the new norm, according to one manufacturer. While OEMs have focused on their blades and nacelle equipment, they have not given the same attention to towers. A height limit for transport, by rail or truck, is about 50m. A panelist at a supply-chain conference said their 12.5-ft width is about the limit for railroad tunnels and not much more for roadway bridges. So third parties have been offering alternate designs. Most are modular and with wider diameters at the foundation.

“Diameters will have to get larger to handle the heights over 100m,” says Jeff Willis, president of Northstar Wind Towers. Wider foundations will also allow less concrete-intensive designs, those shaped more like huge rings rather than thick discs. Willis’ company has designed a modular tower of curved and tapered panels that would more easily ship on flatbed trucks and bolt together into cans or sections at the turbine site. The company has built a 23-m tall proof of concept and plans a 95-m version in Q4.

Another tower idea begins with a wide-diameter concrete base. The large diameter improves stability by spreading tower weight over a larger area, thereby avoiding the large and deep (2 to 3m in some cases) concrete foundations.  An added benefit is more space available for ground-mounted electrical and other turbine-support equipment. “The Concrete Tower Base has features that will optimize existing steel-tower technology and place the focus on height,” says Tindall Corp.’s Chris Palumbo. “For instance, the large-diameter, shallow-ring foundation can reduce material by 60 to 70%.

For the tower base, precast concrete sections are positioned against each other to form a cone-shaped section that provides stability necessary to extend hub heights above 100m. The 50-ton, 26-m long sections transport by truck or rail.

After assembling the tapered base, a circular concrete section fits like a collar atop it. All concrete sections are held together with post-tensioning tendons that loop through the collar sections and around an arched shelf of each taper section. Once the tendons are properly tensioned, the entire structure performs as a unit. A conventional steel tower then bolts to the top of the 31-m tall concrete base. Palumbo says hub heights to 130m and higher are possible.

Wind Tower Systems proposes a lattice-like tower that will allow reaching at least 100m, while they say, lowering installation and transport costs. WTS engineers have been working on the development of this space-frame tower for wind farms that require hub heights of 100-m or more. A durable fabric will cover the space frame to enclose it. WTS also has given thought to ways of transporting and installing these taller towers. They will use standard flatbed trucks and a jacking system to eliminate need for heavy-lift cranes. These developments help cost effectively extend the tower height, which in turn lets the turbine produce more energy.

“Taller towers are an important complement to longer blades,” says Victor Abate, VP of renewable energy for GE Power & Wind. Plans are underway to install a prototype of the GE’s space frame tower to test later this year, with commercial availability targeted for 2012.

WPE

Trends in turbine brakes

Brakes in a wind turbine perform several jobs. They hold blade pitch steady and keep the nacelle pointing in the right direction. Also, that one big disc brake – up to now on the gearbox’s high-speed output shaft to control over over-speed –had better hold everything still when violent storms pass. As OEMs build larger units, over 1.5 MW, braking on the drivetrain is likely to remain a hydraulic function. A thumbnail sketch of trends includes reliable operation, easy service, more complete systems from single suppliers, and overall long-term effort to drive down costs.

Brake manufacturers say operators request smooth, quiet, and reliable braking systems, while O&M crews want easy access to solve maintenance issues. “Low noise from brakes is another trend,” says Colm Gallagher of Carlisle Brake & Friction. “In terms of service, caliper brakes with retractable thrust plates make linings easy to replace.”

To drive costs out of brakes, many companies are working more efficiently –more lean. “The trend in our company, for instance, is to focus on lean manufacturing and lean business processes through a company-wide program,” says Gallagher. “Performance measurements are taken on a daily basis, from the company CEO to machine operators. The system helps drive costs out of business and ensures that purchasing companies receive best possible motion control solutions.”

One research trend is to better understand the nature of friction. Gallagher says caliper brakes are working in the wind market–along with mining, construction, military, and agriculture–so it’s important to understand the “brains” behind effective braking systems–the friction. To that end, his company has purchased others with extensive R&D facilities that focus on brakes and friction.

For electric pitch drives, brakes have trended toward high-torque, electrically released, spring engaged, static holding brakes that can withstand the severe conditions in pitch drives on large turbines. “One pitch brake is rated for 15,000 to 30,000 dynamic stops, depending on coil and voltage required, far exceeding the typical design life criteria of 500 to 1,000 stops,” says Warner Electric’s Engineer Rich Silvestrini.

And where to put the rotor brake is one trend in flux. The rotor brake controls overspeed, and provide parking and emergency braking. These brakes can be mounted on the rotor (low-speed shaft) or on the generator (high-speed shaft), and in some cases on both shafts. Low-speed-shaft braking is relatively straightforward because it is easy to accommodate a large disc brake with a large friction lining area.

The energy to dissipate is the same whether the brake is on the main shaft or the gearbox output shaft–so the total lining area must be the same. But these requirements are more difficult to meet on the high-speed shaft because speed and space will be limiting factors with regard to the maximum disc diameter and brake selections.

The maximum permissible braking torque on the rotor shaft is usually imposed by the blades, or their anchorage to the gearbox input shaft. Also consider that braking on the high-speed shaft is usually related to the maximum permissible gear-tooth loading.

There is also a minimum level of braking torque. Below it, the variable nature of frictional forces from different operating conditions could place the turbine rotors at risk.  Nevertheless, braking on the high-speed shaft has been used on many turbines. Although as the industry develops higher capacity turbines, the trend is leaning towards rotor-shaft braking.

One final trend–as old as it sounds–is one-stop shopping. Gallagher, for example, says his company now supplies hydraulic power units along with the brakes it designs so companies need not patch together brake systems from parts purchased from several companies.

WPE

Michael Schratz
Dialight Corp.
www.dialight.com

AWEA recently reported that, despite significant challenges in 2010, the U.S. wind-power industry made significant progress on its promise to strengthen America’s position with an increased supply of renewable energy. The organization says all signs point to a strong return in 2011. With an aggressive target of supplying 20% of electricity nationwide by 2030, the industry must add many new turbines and wind farms to the grid.

Some estimates peg the number of new turbines required as high as 65,000 between now and 2030. These increasingly large wind turbines will require more sophisticated internal and external communications to maximize their performance and continued public support.

Similar to communication and broadcast towers, bridges, and other tall structures, wind turbines require obstruction-lighting systems to warn pilots of aviation hazards.  Light emitting diodes, or LEDs, have become the technology of choice behind modern aviation obstruction-lighting systems, with adoption and implementation starting nearly 10 years ago.

Historically, LEDs are known for their considerably long life and reliability under extreme conditions.  Of all the benefits LEDs provide, the most important for the wind industry is their resistance to shock and vibration. LEDs are solid-state semiconductor devices that require little power, generate little heat, and do not rely on a fragile filament for illumination.  They contain no mercury or harmful materials and allow for precise optical control, providing the required lighting for pilots while significantly reducing light-ground scatter and disturbance for nearby residents.

 

In addition, LEDs emit nearly undetectable levels of electromagnetic interference and radio-frequency interference (EMI/RFI), a disturbance often emitted by high-voltage electrical circuits that can interrupt, obstruct, or degrade sensitive radio communications. This interruption can be particularly troublesome for radio systems employed by air traffic control and aeronautical communications services. LEDs resolve this problem with extremely low-emission EMI/RFI to ensure reliable communications.

 

Compared to the wasteful conventional L-864 incandescent beacons, which consume 1,400 W and may last less than a year, the latest LED-beacon equivalent consumes only 20 W, or roughly 98% less energy – and delivers optimum performance for at least half a decade backed by an industry-standard 5-year warranty.  Recent improvements in red and white LEDs allow making products significantly smaller, more efficient, and more intelligent.

For their energy and maintenance savings, durability, and low EMI/RFI emission, LED-based obstruction lighting systems will continue to provide reliable, clean lighting technology for the global wind industry for many years to come.

WPE

Engineering a taller tower

Placing wind turbines at greater hub heights puts them in stronger, steadier wind which improves their performance. Wind speed at just one more meter per second can pay off big. Turbine performance becomes a critical consideration as units with larger rotors and greater power outputs enter the market. Taller conventional steel towers, however, are too heavy and too large to transport and erect easily. To make conventional towers more impractical are conventional foundations. They take a lot of prep work and concrete.

One way around the challenges of tall towers is to start with a wide-diameter concrete base. The large diameter provides improved stability by spreading tower weight over a larger area, thereby avoiding large and deep (2 to 3m in some cases) concrete foundations.   An added benefit is the ground-level space available for ground-mounted electrical and other turbine support equipment. Tindall Corp., a manufacturer of precast concrete, has given the concrete-tower base some thought. “The final design of the Atlas CTB (Concrete Tower Base) has features that will optimize existing steel-tower technology and place the focus on height,” says Tindall spokesman for Atlas, Chris Palumbo. “For instance, the Atlas CTB’s large-diameter base uses a shallow-ring foundation that can reduce material by 60 to 70%.  Initially, precast concrete sections are positioned against each other to form a cone shaped bottom section that provides the stability necessary to extend hub heights above 100 meters. The 50-ton, 26-m long sections transport by truck or rail.

After assembling the tapered base, a circular concrete section fits like a collar atop the base. All concrete sections are held together with post-tensioning tendons that loop through the circular sections and around an arched shelf of each taper section. Once the tendons are properly tensioned, the entire structure performs as a unit. A conventional steel tower then bolts to the top of the 31-m tall concrete base. Palumbo says hub heights to 130 m and higher are possible for utility scale turbines.

The final tower has a foundation of about 18-m diameter and one-meter thick. Germanischer Lloyd recently issued a certification report for the Atlas CTB. Palumbo says the company plans to have a prototype installed at Tindall’s Atlanta, Georgia manufacturing facility by summer. Watch an animated construction of an Atlas CTB at: tinyurl.com/atlasctb.

WPA

Vestas facility could produce 1,090 towers per year

Vestas Towers America announced the grand opening of the world’s largest wind tower manufacturing plant. The Pueblo, Colorado facility features nearly 13 million ft² of space and eight miles on-site railroad for the transport of materials and finished tower components.

Secretary of the Interior Ken Salazar joined Colorado dignitaries, as well as President of Vestas Towers A/S Knud Bjarne Hansen and President of Vestas Americas Martha Wyrsch, in making the announcement during a ribbon cutting ceremony. The factory employs more than 400 workers and is capable, at peak, of producing 1,090 towers per year. What’s more, locating the factory along major highway and railroad lines lets Vestas meet customers’ needs with locally managed logistical efficiencies, which translates directly to cost and environmental benefits.

“We have deliberately located factories in a central region in the U.S. – including towers, nacelles, and blades plants – because regional centralization lets us build and ship locally in any direction needed in North America, and that translated to a direct competitive advantage for all stakeholders,” says Hansen.

In the past few months, Vestas Towers America has been actively recruiting and hiring people skilled in a range of desirable jobs ranging from engineering to human resources and from welding to painting. The company has attended numerous local job fairs in over the summer seeking highly skilled employees who have been released from other industries.

Vesta Towers America Inc

www.vestas.com

Taller towers reach higher wind speeds

Four and five-in. diameter tilt-up towers are guyed pipe towers, and come with couplers, end fittings, cables, rigging hardware, turnbuckles, ground anchors, and optional pipe sections. All tower components (except pulleys and zinc-plated bolts, nuts, washers) are hot-dip galvanized. The towers come in heights of 64, 85, 106 and 127 ft. The 4-in. tower accomodates ARE110 and AWP-3.6 wind turbines. The 5-in. tower accomodates Proven’s WT2500, Southwest Windpower’s Whisper 500, and Skystream wind turbines. The appropriate tower makes a significant difference in energy production. In general, towers should be installed at such a height that the turbine’s blade tips (in their lowest position) are 30 ft. above all objects (buildings, trees, silos, and hills) within a 500 ft. radius.
Abundant Renewable Energy

rohnnet.com

Help for machining big wind towers

A portable mill can machine wind towers that now have diameters from 10 to 14 ft, and to a surface-flatness tolerance of 0.002 in. The Climax CM6000 mill can also create a 60 rms micro finish, exceeding the current requirements of the wind-power industry and in particular tower fabricator Hitachi Canadian Industries Ltd., Saskatoon, Saskatchewan, Canada.

Thanks to the modular design of the CM6000 from Climax Portable Machine Tools, Newberg, Oregon, when it is not machining out-of-spec flanges on the assembly line, it can stores in HIC’s fabrication shop until needed, reassembled within 60 min and moved into position by an overhead crane. Its in-situ machining eliminates the time and work required to build subassemblies at a machine shop for re-machining, and the cost of subcontracting with field service companies.

The hunt for the portable mill began when HCI found that work for a particular customer was a challenge because of its short delivery schedule and also, once its larger towers were assembled, the machine shop’s boring mills were not large enough to machine the whole tower to the tight specs required. It had two manufacturing shops including a large machine shop with stationary vertical-boring mills, where subassemblies could be built and towers turned to true-up out-of-spec flanges. But such machining requires hauling tubes from a fab shop to a machine shop, mounting tubes, do the work, and taking them back to the fab again.

As a result, the shop subcontracted the work to field-service companies that used portable machine tools to grind the towers outdoors at the plant. Although the subvendors could meet the precision specs, it was often costly and difficult to schedule them. As a cost-reduction measure, HCI decided to bring the machining in-house. When Chief Engineer Rob McEachern began to research his portable machine-tool options, he contacted Climax Portable Machine Tools.

McEachern and the Climax sales engineer discussed minimum and maximum capabilities of the machine he needed

including its precision, portability, and fast metal removal rate, as well as the range of tower sizes and demanding specifications HCI had to meet. The sales engineer recommended the CM6000 circular mill which had the power, precision, and portability the fab plant needed so it could be used outdoors at the plant as well as set up for use in a work cell. Climax engineers are also designing a fixture to improve the portable mill’s use.

Tower manufacturer breaks ground on new factory

Ventower’s plant construction will complete late 2010. The company plans on building up to 250 towers per year and will begin deliveries by mid 2011.

Ventower Industries has broken ground on its 115,000 ft2, state of the art, wind-tower manufacturing facility. Earlier this year, the company’s design, the Ventower, won an advanced-energy manufacturing tax credit under the American Recovery and Reinvestment Act of 2009. The company was one of 12 to received support from Michigan’s congressional delegation. The company says it is a full service fabricator and supplier of industrial scale, wind turbine towers. Focused on original equipment manufacturers, the company will provide wind towers to wind plants throughout the Great Lakes Region using readily accessible waterborne, rail, and truck transport options.