WindPower 2013: Fair winds, prosperous show in Chicago
WindPower 2013, at Chicago’s McCormick Place, May 5-8, discussed policies, technologies, and benefits related to wind power. Speakers at WindPower’s opening general session included Gov. Terry Branstad of Iowa, who understandably conveyed enthusiasm for wind energy, given the state’s enviable position of having the third largest installed capacity of wind power in the U.S., after Texas and California. Iowa also claims the highest average electricity generation from wind power of any U.S. state, currently running at 24.5%.
Gov. Branstad, a long-standing advocate of wind energy, mentioned that Iowa accounts for an estimated 7,000 wind-energy related jobs, ranking the state No. 1 in that category. Branstad remains excited about wind energy’s future and the progress being made, but cautioned that policy stability and predictability are key requirements for the industry’s long-term success.
Welcoming remarks of Rahm Emanuel, Mayor of Chicago, to WindPower attendees extended into industry topics. “Thirteen wind power companies are based here; and 150 companies in Illinois are engaged in some form of wind energy,” Mayor Emanuel said. His statement that in 2012 Chicago closed two coal-fired power plants—the last located within a U.S. city—drew enthusiastic applause.
Tom Kiernan, incoming CEO of the American Wind Energy Association (AWEA), also spoke briefly to the overflow audience of the general session. He likewise stressed the need to create a fresh long-term plan for the wind power industry and AWEA. Kiernan begins his tenure with AWEA on May 28.
600 exhibitors; conference sessions
Approximately 600 companies exhibited products at WindPower 2013. Most prominent were the large wind turbine manufacturers—complemented by a gamut of ancillary system, equipment, and services suppliers. Among product areas of prime interest to the engineering community were gearboxes, generators, transformers, inverters, controls (electric and hydraulic pitch/yaw subsystems, SCADA, software), and technical services (such as operations, maintenance, consulting, safety, and testing/certification).
A major part of WindPower’s conference portion consisted of paper presentations running in several parallel sessions. Besides a scientific track (resource assessment; structures, dynamics, loads, and control; technical challenges), conference topics ranged widely from market update, supply chain, and the international scene to finance, offshore, state policy, and wind power integration.
One of the scientific sessions—Innovative Wind Turbine Components R&D, moderated by Dr. D. Todd Griffith, offshore wind technical lead at Sandia National Laboratories—focused on turbine blades, gearboxes, and sound mitigation as summarized in the following four papers:
“Advanced Technologies for the Design and Manufacturing of New Wind Turbine Blades,” presented by Carlos Amezqueta, mechanical engineer, Spanish National Renewable Energy Centre (CENER), addressed new techniques under development at CENER and being implemented in a 13.4-m (44-ft) length turbine blade, which will serve as a “technological demonstrator” to apply to much larger blades. Amezqueta cited these current CENER developments:
- Structural lightening—made possible by use of carbon nanofibers mixed in the epoxy resin to improve compression and fatigue performance of glass fiber-reinforced composite parts. The best percentage composition of carbon nanofiber in the resin was investigated.
- Manufacturing automation—helping to reduce process variability, which is vital to maintain turbine blade quality. The resin transfer molding process used eliminates the need for bonded joints and is appropriately monitored to obtain repeatability, high quality, and blade robustness. Among process challenges mentioned by Amezqueta is handling the heat generated in the exothermic reaction that occurs especially in thicker sections of the blade structure.
- Aerodynamic performance enhancement—included adding an aluminum winglet at the blade tip and use of a new blade coating. The winglet improves energy efficiency and simplifies lightning protection, while the coating reduces adhesion of water drops (icing) and other atmospheric particles on the blade surface that cause detrimental airfoil geometry changes, according to Amezqueta.
- Blade instrumentation—strain-gage sensors specially suited to stress measurement in composite materials, known as Fiber Bragg Grating (FBG) sensors, were embedded at the blade root and at six points along the span of the blade. FBG sensors allow implementation of wind turbine advanced control algorithms, such as individual blade pitch control and structural health monitoring for product life extension.
As an aside, Spain reportedly accounts for the fourth largest electricity production from wind in the world and essentially the largest production in Europe.
“Experimental and Computational Study of Dynamic Transient Loads in a Wind Turbine Gearbox” was the topic delivered by Zhiyu Jiang, PhD candidate, Norwegian University of Science and Technology (NTNU). The basis of this paper was research results from gearbox modeling and testing done by two agencies: the Gearbox Reliability Collaborative project of the National Renewable Energy Laboratory in the U.S. and the NTNU.
One project objective was to evaluate gearbox response under field conditions. Current work has expanded into field-test measurements and greater emphasis on gearbox transient events—after validation of dynamometer test measurements performed earlier, according to Zhiyu Jiang. Two cases of gearbox transient events examined were start-up and emergency-stop.
“Transient [field] events cause large loads in the wind turbine drive train and pose high damage potential,” Zhiyu Jiang said. For that reason, accurate simulation of transient events becomes important.
The gearbox studied was a three-stage unit, with one planetary gear stage and two parallel gear stages. The gearbox was “heavily” instrumented with sensors to measure strains and loads; however, only planetary bearing loads were measured, he noted.
Zhiyu Jiang expects further validation of gearbox multi-body modeling techniques to come from internal gearbox measurements of the field testing. This is expected to yield “deeper insight into modeling requirements to predict gearbox loads during field load conditions.”
Focus on wind turbine gearboxes continued into next paper, “A New International Wind Turbine Gearbox Standard,” by Brian McNiff, owner of McNiff Light Industry. Under development over the past 6 years, an international standard on wind turbine gearing has been published. McNiff explained that the need for such a standard came from the substantially different application environment for gears in wind turbines compared to industrial gearboxes. “There was also the need to facilitate communication between manufacturers and users of gearboxes,” he said.
The official name of the new International Electrotechnical Commission standard is IEC 61400-4 Ed. 1.0, Wind turbines – Part 4: Design requirements for wind turbine gearboxes. IEC 61400-4 applies to enclosed speed-increasing gearboxes for horizontal-axis wind turbine drive trains with power rating greater than 500 kW—including onshore or offshore installations.
Development of the standard involved substantial peer-level cooperation, according to McNiff. “More than 70 experts from 12 countries from the wind turbine, bearing, gear, and lubrication industries were involved and 17 meetings took place,” he said. This working group built on a prior U.S. standard—ANSI/AGMA/AWEA 6006-A03 published in 2003—which was jointly developed by the American Gear Manufacturers’ Association (AGMA) and the American Wind Energy Association.
“The Joint Working Group on wind turbine gearboxes was a cooperation between IEC Technical Committee 88 (wind energy) and ISO [International Standards Organization technical committee] TC60 (gears) [along with] significant participation from ISO TC4 (bearings) and ISO TC28 (lubricants),” McNiff added.
A number of changes are part of the new standard, including areas such as loads, testing, bearing selection, and lubrication—which can lead to improved gearbox reliability. Other expanded coverage in IEC 61400-4 includes:
- Expanded analysis of gearbox structures
- Dynamometer testing of any new or modified gearbox design
- Recommendations for lubricant performance, including filtering and cleanliness requirements
- Cooling requirements.
Overall, IEC 61400-4 provides guidance on gearbox design, performance, manufacture, and testing specifically for wind turbine application.
Less noisy turbines
A final paper, “Concepts for Wind Turbine Sound Mitigation,” presented by Dr. Kevin Kinzie, engineering manager at General Electric Co., covered the personally subjective topic of turbine noise. Several general noise reduction concepts were presented. Wind turbine operation itself affects sound levels. Noise is proportional to blade speed, but reducing speed may not be a practical solution.
Sound mitigation must start with an understanding of the dominant sound sources, Kinzie noted. These sources were reviewed relative to their importance to overall sound levels. “Blade trailing edge and blade tip noise are such dominant sources,” Kinzie said. Therefore, noise mitigation methods centered on these two areas of the turbine blade.
Part 1 of mitigation concepts involved the design and noise testing of several blade tip geometries on a 2.5 MW-class wind turbine. Tip shape had a significant impact on blade noise signature, particularly in the higher frequency range, according to Kinzie. Modified (low noise) tip shapes resulted in 5–6 dB(A) lower apparent sound power level compared to a baseline blade tip design.
In part 2 of the developments, various blade trailing edge noise-reduction concepts were screened using wind-tunnel testing. Trailing-edge serrations showed promise and were selected for full-scale field tests. Three wind platforms equipped with different blade trailing-edge designs showed 2–4 dB(A) less apparent sound power level versus original (unserrated) blades.
In summary, Kinzie presented a general methodology for optimal wind turbine operation to meet noise level regulations while maintaining maximum energy yield.
The American Wind Energy Association runs various programs and events nationally throughout the year. Next year’s main event—WindPower 2014—is scheduled for May 5-8, 2014, in Las Vegas, Nev.
– Frank J. Bartos, PE, is a Control Engineering contributing content specialist. Reach him at firstname.lastname@example.org.
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