Windpower Engineering & Development - AUGUST 2016

GOOD THINGS UNFOLDING IN THE WIND INDUSTRY /

WindWatch page 10 August 2016

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A BETTER WAY TO INSPECT

turbines & transmission Analyzing the lifeblood of wind turbines PAGE 36

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HERE’S WHAT I THINK

Editorial Director | Windpower Engineering & Development | pdvorak@wtwhmedia.com

The next 10 darn-near impossible grand challenges for the wind industry

T

he idea of grand challenges came from DARPA, the Defense Advanced Research Projects Agency in the 1980s. The challenges are stretch goals or difficult tasks that if accomplished would propel an entire industry forward. DARPA funds what appear as wacky ideas that could be useful to U.S. military forces. One recent Agency idea is a device to make things invisible, such as tank or soldier. Cool if possible. President Kennedy’s proposal to put a man on the moon was certainly a grand challenge that energized the space race. You get the idea.

This column has explored the idea of grand challenges for the wind industry once before in 2012. Three years later, the industry had hit three challenges. Four challenges were near hits, and three are still unmet. One challenge, active

surfaces for more precise control, has been meet by Frontier Wind’s Gustbuster blade tabs. Sadly, Boulder Wind, the company that met another challenge by devising a lightweight, direct-drive generator has since closed its doors.

The time has come to revisit the grand-challenge idea and replenish the list. But this time, rather than rely on my own idle mind, I have enlisted the imagination of two talented people: Senior Editor Michelle Froese and CMS expert and contributor David Clark. He suggested defining challenges for OEMs and the O&M community. Good idea. So we pose this set of grand challenges for the OEM community. We’ll get to the maintenance industry later.

So without further fanfare, here in ascending order are the 2016 Windpower Engineering & Development Wind Industry OEM Grand Challenges:

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10. Make condition monitoring standard for every 4. Gearboxes capable of working 20 years without major turbine. The only way to knock down maintenance repair. By one estimate, a gearbox costs up to $500,000 costs is with predictive maintenance and CMS is key. to replace. Trimming two replacements could make each turbine $1 million more profitable. Aerotorque’s torque 9. Self-erecting towers or turbines. We’ll take either. limiter is a step in the right direction.

8. The 10-MW land-based turbine. This development may depend on at least a 90m blade. The longest in the world, 88.4m, will go on an 8-MW turbine, but might work on a 10MW design.

7. Lightning hit identifier. Which turbine blades have holes in them thanks to the last thunderstorm? Who knows?

6. A light weight, direct-drive generator that could eliminate the need for gearboxes.

5. Blades that will survive 20 years of operations.

3. Smarter turbine controls, those that “know” what ails the turbine and tells an O&M crew so it need not waste time troubleshooting. Even better, controls that fix or detune the turbine to keep working till help arrives.

2. Less costly, high-capacity energy storage, capable of many megawatt-hours.

1. Less expensive and mass producible superconducting cable conductors. (Same as last time) Such cables would allow the transmission of power with little loss to load centers many miles from the wind farm. Wind assets would not sit idle as they sometimes do in the northwest because of a lack of local demand. ABB’s high-voltage dc is a step in the right direction.

If you know of a company that has genuinely met one of these challenges, they have been keeping secrets. Tell us about them. OK? W windpowerengineering.com

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DORWROTH CHANDRABALAN

CO NT R I BUTORS

HALEY

SANTHOSH CHANDRABALAN leads the 3M Wind business in his capacity as the Global Business Manager.

Chandrabalan’s experience includes research in composites, process engineering, engineering management, global key account management, and more. He is an active member and held leadership positions in many global wind and composites’ communities and consortiums. He holds a BS in Composites Material Engineering from Winona State University and MS in Engineering Management from Southern Methodist University.

KARPENSKE

HESLEHURST

LOUIS C (LOU) DORWORTH has been involved with the advanced composites industry since 1978 and has worked at Abaris Training since 1989, where he currently manages the Direct Services Division. By trade Dorworth is a composite materials and process specialist with experience in research and development (R&D), material and process (M&P) engineering, manufacturing engineering, tool engineering and design, and tool fabrication. He has considerable background in repair of advanced composite structures. Dorworth is a primary coauthor of the textbook titled Essentials of Advanced Composite Fabrication & Damage Repair, ASA 2009.

MEADOWS

LEAVERTON

JAY HALEY, PE, has been involved in wind energy since 1983 and is the Principal in Charge of the Wind Energy team at EAPC in Grand Forks. He has made hundreds of public presentations on wind energy and has been the wind industry’s primary spokesperson in North Dakota. Haley provides consulting services to wind developers, financial institutions, electric utilities, communities, economic development groups, universities, and Native American tribes.

PROVOST

MURYWED

MOSESON

RIK HESLEHURST is a former aeronautical engineering officer in the Royal Australian Air Force. During his 16 years military service, Heslehurst was in charge of the RAAF Material and Process Engineering Section and an airworthiness engineer on the F/A-18 Hornet aircraft. He recently retired as an academic from the University of New South Wales at the Australian Defence Force Academy (UNSW@ADFA) after 20 year of academic service. There he lectured in aircraft design, airframe design and analysis, structural joining methods, damage analysis and repair design, and composite structural design.

Heslehurst is currently the Senior Engineer for Abaris Training, and also consults for the Australian Defence Force, Civil Aviation Safety Authority, NASA, USAF, Boeing Airplane Company, Bombardier Aerospace, and many others.

WATERS

SCHENK

DAVE KARPENSKE, appointed CEO in December 2013, leads the growth and development of PCN strategies and products.

Prior to PCN, Karpenske was Vice President of Strategic and Corporate Marketing at JDS Uniphase, a global leader in communications test and measurement, commercial optical products, and optical security and performance technologies.

He was also at Schlumberger, working as President of North and Central America and responsible for Schlumberger’s telecommunications, semiconductor equipment, smart cards and IT managed services.

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GRANT LEAVERTON is the General Manager at AAIR Team.

AAIR was one of the first firms in the U.S. to be approved by the FAA for commercial unmanned aerial system (UAS) operations. The company provides leading-edge aerial inspection and data analytics for the utility, renewable, and energy and infrastructure markets. Leaverton has a Bachelor’s in Industrial Engineering from Texas A&M University and a Business MBA from Southern Methodist University.

BECKI MEADOWS, a consulting engineer with Romax Technology, graduated from the University of Michigan with a degree in mechanical engineering and went directly to work as a field engineer for GE’s Power Generation division. There she inspected and repaired steam turbines and generators at small to medium power plants across the country. In her five years with GE, she was trained in statistics and process management, which lead to a career as an independent consultant, trainer, and co-author of a book on how to use statistics to effectively manage business. Prior to joining Romax, she worked as a senior engineer at the National Renewable Energy Laboratory (NREL) completing wind resource assessments for the federal wind program and cost of energy modeling for distributed energy and offshore wind projects.

JUDAH MOSESON, is the Vice President of Operation at Cooke Power Services. The company specializes in wind turbine maintenance, high voltage services, and maintenance for the balance of plant equipment. In previous positions, Mr. Moseson has been responsible for O&M services at Cielo Wind and Technical services at Infigen.

MOHAMAD MURYWED is Sales and Business Development Manager for ABB’s Wind Retrofit Global Services in Barcelona, Spain. He is an electrical engineer with experience in wind energy, smart grids, and oil and gas. He holds a Master in Business Administration and is focused on offering advanced services to wind industry.

DAN PROVOST is president of New World Technologies, developer of RadTorque Systems.

UWE SCHENK joined HELUKABEL in 1998, and is currently the Global Segment Manager – Wind. He has overseen the company’s involvement in the wind industry for the last 10 years. Schenk has a fondness for Elvis music and is known within HELUKABEL as “The Godfather.”

NICHOLAS WATERS is the Key Account Manager for Bachmann electronic North America. He joins the wind industry with a background in research and development focused on structural health monitoring (SHM) and condition based maintenance (CBM). Nicholas is a Mobius certified Category II Vibration Analyst with a M.S. in Ocean Engineering from FAU and a B.S. in Applied Mathematics from UC Davis.

www.windpowerengineering.com

AUGUST 2016

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AUGUST 2016 • vol 8 no 4

CONTENTS

D E PA R T M E N T S 01

Editorial: More darn-near impossible grand

32

Projects – Transmission: A developers guide to transmission

06

Windwatch: Research in Minnesota, MAKE

34

Cables: New standards favor UL-listed cable for wind turbines

36

Lubricants: Analyzing the lifeblood of wind turbines

22

Condition monitoring: A word about sensor

38

Inspections: Best practices for end of warranty inspections

selection for CMS

40

Materials: Best practices for blade protection and repair

26

Retrofits: New ideas for upgrading communication networks

43

Repairs: Simplifying blade repairs with zoning and structural methods

30

Bolting: Think calibrations to keep bolting

58

Ad Index

60

Downwind: U.K. inventors want to tap into 100-mph winds way up

challenges for the wind industry

Consulting looks ahead, Better blades ready for refits, Meet the wind tech

tools accurate

54

F E AT U R E S

47 A wind farm’s balance of plant also needs an inspection

The balance of plant (BOP) is the most important link for delivering power produced by a wind farm to the marketplace. The BOP consists of the padmount transformer at the base of the wind turbine through to the collection system and substation.

The BOP also includes transmission lines, met masts, and the roads and drainage.

xx

Drones to play a bigger role at wind farms The commercial drone industry is rapidly evolving. Each advancement means application of Unmanned Aircraft Systems (UAS) can enter another market and provide a service that typically cuts costs and enhances safety.

ON THE COVER

An AAIR drone provides blade, tower, and transmission inspections for a Texas wind farm.

50 Wind turbine upgrades get legacy

turbines ready for a more productive and longer life While new wind turbines have their place in the wind power mix, there is a growing demand to upgrade assets of an older age.

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High Speed Shaft Solutions

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Protects wind turbines against peak loads, reverse torques and grid shorts.

Established designs for slip torque values ranging from 4,000 to 50,000 Nm. • Designed to protect both the gearbox and generator from extreme torque and damage • Generator shaft mounted to avoid resonance concerns and installation difficulties • Proven and tested to 5,600 torque events of 30°

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BIG BIGBLADES BLADESARE ARENOT NOTYET YET HITTING HITTINGHARD HARDLIMITS LIMITS ON ONSIZE, SIZE,SAYS SAYSDNV DNVGL GL

THE ECONOMY OF SCALE says make turbines bigger and the production cost of power comes down.

While one manufacturer has done its part by unveiling an 83.5-m long blade, the R&D effort is to make blades longer still. (Since this conversation, an 88.4-m long blade has been unveiled) “Large blades are in rapid development at several OEMs,” said Dayton Griffin at the recent AWEA WINDPOWER conference. The Senior Principle Engineer with DNV GL has been involved with blade engineering for 21 years.

The good news, he says, is there seems few limits to blade length even with current technology.

When he launched the first scaling study in 2000, Griffin said he expected to find some fairly non-negotiable limits with the current technology, and say, ‘Okay, at this point, we need something fundamentally different to go bigger.’ “I've been doing scaling studies looking at limiting blade technology since 2000, but have not encountered a hard stop. If we can do 83 meters, 100 meters is feasible,” said Griffin.

The 100-meter blade is out there. The 83.5-meter blade was delivered by SSP Technologies in Denmark for a Samsung Heavy Industries’ 7-MW prototype. That blade allows for a 170-m diameter rotor. The three-blade turbine was erected as a single prototype in Scotland.

Samsung has since exited the offshore market and the turbine has been acquired by a research academic consortium in Europe, available as a public-domain research turbine.

“The longest blade is nearly a step change in size for the industry which is rapidly moving on a scale for which it does not have a lot of experience.” He added that it seems the industry has not yet solved all problems with 40-m blades, and now it is going up to 80 m.

One engineering strategy for longer blades has been to use thicker airfoils so they have more inherent flexural stiffness. “There are limits because a blade that’s too thick does not necessarily perform well from a lift-over-drag standpoint. So far, construction has fallen onto two tracks. One just increases the amount of glass fiber in the structure,” said Griffin.

Blades are normally built by placing dry materials in layers and infusing them with resin. “There's a limit to the amount of fiber volume you can get. Fibers are the stiff part and plastic resin holds them together. It's like rebar in concrete, if you will,” Griffin explained. Various techniques, such as prefabricated rods, are used to incrementally increase a blade’s fiber content in critical areas of the structure.

The other design track deals with alternative fibers. “This again, breaks into two tracks. One is to give the fiberglass a higher modulus. Intermediate-modulus and high-modulus glass fibers are mainstream now.” The other fiber track is to use alternative materials. Carbon fiber, of course, is the most commercialized. However, companies are continuing to investigate other fibers that also have good stiffness-to-weight ratio properties.

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W I N D W A T C H

”For the traditional, industrial polyacrylonitrile or PAN-based precursor to carbon fibers, we're probably not going to see major breakthroughs. Improvements will be incremental with regard to capital equipment and the raw materials. I don't know how the reduced price of oil might feed into carbon, because its precursor is petroleumbased. It's conceivable the cost would come down. But what comes down can go back up again,” said Griffin.

“There's no innovation there. The two most expensive parts of the process are a petroleum-based product and energy, and it takes a lot of heat to make carbon fiber.”

The longest blade is nearly a step change in size for the industry which is rapidly moving on a scale for which it does not have a lot of experience.

The Oak Ridge National Laboratory has been working on potential break-through technologies for carbon fibers.

“It has used alternative precursors or alternative chemistry.

That's still mainly in the realm of R&D, though in early 2016 Oak Ridge announced they are ready to offer one low-cost carbon technology for production use on a licensing basis.”

The cost of carbon fiber for a blade is roughly 8 to 12 times that of fiberglass on a unit-weight basis. Aerospacegrade carbon is in the range of 2 to 4 times higher than the industrial carbon fibers. . “We use the industrial stuff in turbine blades, not the aerospace fibers. In addition to the cost element of carbon, it's tremendously fussy – hard to work with and very sensitive to angular variations and transitions. Those sensitivities are addressed in aerospace construction because they use much finer materials and are more careful in the placement for a higher-performing structure,” said Griffin.

Although the fiber is stiff and strong, if the alignment is off, it can initiate damage. So if the industry decides to use carbon fibers for proper alignment, it is important to ensure carbon does not become the weak link and use robot weavers – more automation.

dimensional studies to help figure out how long, wide, and tall it should be, and what load capability it should have.

At that time, it was our intent to allow blades up to 100 meters, though maybe not with the entire blade in the lab.

We ended up being able to test most of an 85-m blade in whole. The SSP 83-m blade was tested at the Fraunhofer Institute in Germany.”

One option to testing long blades is to cut off the last 10 m or so and reinforce it. “Structurally, that's acceptable.

We still get good results with a less than complete blade.

Other test laboratories have capability for up to 80 m. It depends on the details of the design and the test. For example, how much deflection will be tested, and how much clearance is needed for deflection? The 80 to 100-m blades are about the limit of our test capability today,” he said.

Controlling blade loads The industry must continue making parallel advancements in load-mitigating technologies,” Griffin added. “Bigger blades must go on smaller machines, and we should continue to grow the size of rotors for larger machines in a cost-effective way. Some load-mitigating technologies can simply be in the controller. Many things can also be done, passively and actively, on the blades for loads control.”

Failure in blades Regarding failure modes, Griffin said there are progressive damage modes that may be caught before a blade fails catastrophically. Those include leading-edge erosion, trailing-edge separation, and delaminations of various kinds. Lightning protection is also a concern with carbon.

“There are various damage modes that we can detect. I call it failure when the blade becomes unrepairable.”

Blade testing With regard to testing, DNV GL was the consultant for the Boston structural test facility, the WTTC. “We did the 8

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W I N D W A T C H

blades, condition monitoring, structural-health monitoring, awareness of the loading condition to make decisions, whether they be at the torque and speed level, or the pitch level. “We're going to see this development spread for at least 10 years thanks to robotics, MEMs (Miniature electro-mechanical sensors), and other miniaturized technologies becoming more durable and less expensive.”

Griffin said his group has performed a conceptual design study on active aerodynamic devices. The intent is to have something small and fast acting that can respond much quicker than pitch systems.

Microtabs have been considered. “The tabs could either spoil aerodynamics, or increase or decrease lift. It's a small device that pops in and out the blade, and was included in our study. Other active technologies include boundary layer suction and blowing, and circulation control, which takes a non-lifting shape and turns it into a lifting shape. That's pretty interesting. All these technologies have already been commercialized in one or more aerospace application.”

What’s next We are moving toward a goal that is not about minimizing load on the blade. “The effort is to optimize revenue relative to life consumption.

The turbine is a power plant and owners want to make the most money out of their investment. So we are

The next generation ”When talking about active control, I use the aerospace term ‘buying itself onboard.’ The question is: what will it take for these technologies to buy themselves onboard a blade? For example, the most well-known passive control is in-plane sweep, like the Star rotor blade (from Sandia Labs). Siemens has now commercialized in-plane sweep.

Wing sweep is well-recognized, and mature technology in aerospace. The feature is now mainstream in the wind industry, although it is not universal.”

A next blade development might mean blades “know” what is happening.

“The blades become ‘self-aware,’ so to speak. A great presentation came from LM Blades at a conference in China a few years ago. The company was considering a 70-m blade which at the time would have been an industry first. The engineer who spoke said the wind industry was entering a new era in blades. The speaker recounted how the industry first came through an era of airfoils in which airfoils were made thicker and designed for more robust laminar flow.”

That was followed by the era of materials, when industry looked at things such as high-modulus fiberglass and carbon fiber. The industry is now looking at processes that will get more fiber into the structure, said the speaker.

Now, continued the speaker, we are at the beginning of the era of electronics in the blade. Sensors, controls, smart WINDPOWER ENGINEERING & DEVELOPMENT

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developing the knowledge, skills sets, and tools to start looking at the world that way. Not just on a turbine basis, but on a wind farm (or power plant) basis.”

Griffin said significant lessons have come from scaling studies. There is a tendency to freeze technology, such as transportation or erection technology.

Freeze that, and just work on the blade, making them modular, for example.

But it is wrong to assume all of the other technologies are static. They are not, he said. For instance, when the blades get bigger, the transportation folksget creative. The crane people get creative and they innovate around limitations. “Boundaries move and other parameters in the study move. It's a good thing because we're not hitting hard limits. We're engineering our way around them.” W

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W I N D W A T C H

Good things unfolding in the wind industry says MAKE Consulting THE PTC EXTENSION has been the most substantial news for the wind industry in recent months, but there are many other positive developments. For instance, average turbine nameplate ratings are trending towards 3 MW, which surprisingly may cost a bit less to install than smaller 2-MW class machines. Today’s turbines are capable of achieving gross capacity factors in excess of 50%. The next generation of wind turbines due for release over the next three to four years will be competitive with natural gas without the tax credit. That was the news from MAKE Consulting Partner Dan Shreve as he kicked off AWEA’s Windpower 2016 in New Orleans in May. The big news over the last few weeks has been the unexpected four-year COD (Commercial Operation Deadline) associated with the recently extended production tax credit. “It makes the full, 100% production tax credit available through 2020. One consequence has been an upgrade to our forecast for Q2. We're forecasting an additional 7.7 GW on top of our first quarter base case scenario,” said Shreve.

Vestas provides an example of portfolio development. For instance, the current crop of best in class technology is already 12 to 24 months old in a 36 to 48 month cycle. OEMs must demonstrate what their product pipelines can deliver within the PTC time constraints.

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What’s coming, what’s new In terms of the overall total market, Shreve sees over 70 GW of aggregate demand through 2025. "That is fantastic demand that provides great business certainty,” he said. What's more, that business certainty can aid in driving R&D efforts that will lower the unsubsidized cost of wind power to around $46/MWh. There are market drivers and market barriers in his forecast. “Coal-plant retirements will be a driver in terms of the need for new capacity, and utilities are preparing themselves for the Clean Power Plan.

Wind will be competitive with fossil generation but is facing more competition from solar across the global renewables market. Commercial and industrial demand is also a driver. In the later stages of the forecast period, 2020 to 2025, the Clean Power Plan starts to take over from the PTC.” When talking about the major macro-economic drivers, not much has changed. Natural gas prices continue to linger at low levels, about $2 to $3 per million BTU. “This is the primary challenge to wind. It sets the marginal power prices and is the real competition.”

Shreve also forecasts low load growth. “We're talking about growth of around 0.8%. Energy efficiency measures will also reduce load growth.

Removing coal-generated power will allow more wind industry growth. “Will the loss of coal plants be a driver for wind adoption in the Southeast? Possibly.

That area’s lesser wind resources are a challenge.

However, this is good news for Texas which might find markets for its power to its east,” he said.

Over time, how might construction and demand change? “We're hearing more discussion regarding larger turbines and how modular technology can open up new regional markets, specifically in California and New England.

C&I (commercial and industrial buyers) activity is growing, with non-traditional power buyers such as Google and Facebook. “They're not IPPs, but we expect a sizable chunk of the market to be represented by those types of buyers. We're talking about 16 GW of demand, separate from the commercial and industrial segment. The PPAs through 2017 total about 2.5 GW with expectations for another 13 GW moving forward.

It's incredible to see how company leaders are looking at wind as being a long-term power hedge.”

www.windpowerengineering.com

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In addition, many companies interested in renewable energy are not power people. “They're data people, internet folks, organizations without power generation as core competencies,” said Shreve.

Those inclined to think long term now have more time to understand the markets while brokers have more time to figure out how to reach the Tier 2 companies. They are the next step. “We've got the big guys, such as Google and Apple. Now how about the Tier 2 people, those that don't need 200 MW? What about companies that need 20 MW? How can we make a cookie-cutter type of financial approach in which you can get that next tier of demand into the construction pipeline?”

The next generation The next generation of wind turbines, coming in the 2020 timeframe, is expected to improve on today’s models. “We've been pleasantly surprised to see how quickly the LCOEs came down. We had to do a lot of digging this year because, quite frankly, we didn't believe our own numbers. The turbines are getting better giving wind a great story to tell.”

OEM turbine portfolios rotate through products on a three to four-

The Great Plains, the wind belt, remains the focus for U.S. developers given its world-class resource and ease of permitting. There is opportunity for the installation of larger turbines on the east coast as capacity factors continue improving. Low hydropower prices inhibit demand in Pacific NW. Strong solar resources moderately hinder wind development in the southwest.

constantly fighting against a 12-month on-and-off cycle. Planners are now saying, ‘Wow, we can actually do long term technical and strategic planning'."

Shreve mentions the next four-year time frame. “For example, the V110's

Will the loss of coal plants be a driver for wind adoption in the Southeast? Possibly. That area’s lesser wind resources are a challenge. year cycle. “The additional demand and production tax credits are fantastic, but they complicate things. Whether developer or turbine OEM, few are used to working in a four or five-year timeframe. Everyone has been operating in a fire-drill mode for the last five years, AUGUST 2016

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have already been out for two years. I'm expecting that machine to go over 2.2 MW with one more rotor upgrade that could take advantage of the current safe harbor.

Then what? On to the 3-MW platform. But first focus on fulfillment. Developers are like minded, and may ask, ‘Why wait for

the next best thing?’ Put in the 2.2 MW turbines. They won’t be obsolete. But we've seen that when the product evolves, it gets bigger, better, AEP improves, Capex gets better, and installation capabilities improve. But the question remains: What happens in three years when the next best machine comes out? How can developers and OEMs figure out how to include these new units within the existing PTC safe harbor arrangements.”

Here’s why Shreve expects more 3 MW turbines soon. “The Vestas V136, for one, has a gross capacity factor of 55.7%. Could you imagine even saying that five years ago? Not really. If you look at the size of the machines and their capabilities, measured to lower construction costs, it's really eye-opening stuff. A migrations towards 3-MW turbines is the trend.” W

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ETa Blade CEO Giovanni Manni says his company has two possible business models for reblading: sale of components or long-term full service. The company will be active in the U.S. through its partner Weir-YES. Replacing original equipment blades with a design from eTa Blades, Fano, Italy, provided a 20% boost to AEP. The eTa4x blade has been designed for the reblading of Gamesa G47s, Vestas V47s, and turbines from other manufacturers. Test results and a case study are available at: http://www.etablades.com/re-blading/

Goodbye old blades, hello 20% more AEP A RECENT FIELD TEST performed on a V47 turbine equipped with new blades by eTa Blades confirms that reblading (in this test, replacing 15-year old turbine blades with new designs) is an effective way to boost production on aging wind farms. The tests, performed in Italy by qualified industry advisors, show that the eTa4x blade can deliver a net AEP increase of +20% when compared to the original Vestas V47 blades. What's more, the new designs reduce loads on the turbine and produce no additional noise.

“We have completely redesigned the original blade and added an additional meter in length,” says eTa Blades CEO Giovanni Manni. “The design ensures that all turbine constraints are taken into account and no risks are hidden in the use of the new blade.”

Reblading has become one strategy for eliminating the symptoms of aging wind farms. “The production boost has been made possible through the adoption of the most advanced design and manufacturing techniques, which include new aero-elastic concepts for auto-adaptive profiles and geometries on innovative aerodynamic profiles and use of materials in manufacturing unavailable 15 years ago,” says Manni.

In particular, the benefits of reblading come from new airfoils, the use of aero-elastic concepts, such as bend-twist coupling for blade deformation in high wind, and above all, more recent composites including new foams, carbon fibers, 12

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The winglet has two functions. One is to reduce noise. The new blades are a meter longer than the old version and on fixed-speed turbines, the added length could have resulted in a noise increase. Manni’s team had to make sure that it was not exceeding the levels prescribed for the test site. The second reason is to improve performance at low wind speeds. At 3 to 4 m/s, the winglet is said to provide 2% more power over a conventional design.

and others. Manni says his goal is to significantly enhance the cash flow of the assets, at the same time optimize the LCOE. Reblading helps keep operating costs under control and at acceptable levels.

Another plus: the new designs make marginal sites exploitable.

An indicator of wind-farm aging, says Manni, is when it shows increasing degradation on main components, mainly blades,

www.windpowerengineering.com

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gearboxes, yaw drives, generators, and pitch controllers. The number of failures per year increases. On blades, for example, aging appears as leadingedge erosion, gel-coat debonding, accumulation of dirt and grease, and cracks in the laminations.

“We have quantified the impact of wind-turbine aging and it’s shocking: downtime per turbine doubles over the years, and it increases during the second decade of operation,” says Manni.

However, the most evident symptom of an aging wind farm is the increasing cost of maintenance. In addition, OEMs have either disappeared or are no longer serving old turbines. Main turbine suppliers tend to focus on newer and larger models, so reblading is an unserved market that needs filling. W

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The coefficients are for power and torque versus wind speed for the eTa design.

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130-m met tower ready for research at U. of Minnesota

NOT ALL WIND RESEARCH LABS are in Texas. One well-kept secret is the wind energy research program at the St. Anthony Falls Laboratory of the University of Minnesota. The lab owns and operates a field research station which features a 2.5-MW Clipper Liberty C96 wind turbine and 160m to the south of it, one of the tallest and well-instrumented meteorological towers in the country.

“Our 130-m tall met tower is equipped with four sonic anemometers from Campbell Scientific and six cup-and(LEFT) The picture, research from a fascinating video (www.eolos.umn.edu/ node/367) taken during a snowfall, shows the Clipper’s blade tips sweeping through the snow flakes, revealing tip vortices and their interactions. The setup includes a 5-kW spotlight, its generator, a convex mirror to create a light sheet, and of course, the snowfall.

The 130 met tower works with a Clipper Liberty at the University of Minnesota’s facility in Rosemont.

The tower sports four sonic anemometers, six cup and vane anemometers, six temperature probes, and more.

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vane anemometers,” says Chris Milliren, SAFL Associate Engineer. Sensors are located at elevations corresponding to the top and bottom of the rotor swept area, hub height and other elevations in between. Campbell Scientific assembled the full sensor system, programmed and tested it in their Logan, Utah office and then shipped it to Minnesota to be installed on the met tower in Rosemount., The enviable setup was made possible by a DOE grant in 2010 that included purchasing the Clipper Liberty turbine.

The met tower and turbine are located in Rosemont Minn., about 30 miles from the University of Minnesota campus.

Located 160m upwind of the wind turbine in the predominant wind direction, the met tower provides detailed measurements of the incoming flow profile. “We also have a WindCube, a lidar unit that can be placed anywhere. Grad students conducting wake studies often wait till the met tower is upwind and then place the lidar unit downwind in the wind turbine wake.”

Milliren’s team also installed a bladesensor system on the Clipper wind turbine in collaboration with Sandia National Laboratories. “We have strain gages and accelerometers in each blade.” Equally impressive is that his team built a robot-like device to install accelerometers inside the blade. “We called it a robot on a stick. It rolls on six wheels and was pushed into the blades with a 110-ft pipe. When it reached the correct location, pneumatic cylinders were activated to glue the accelerometers in place. Each blade has two accelerometers located 35 meters from the hub, or at about 73% of the blade length.”

The turbine also has 20 strain gages around the base of the tower to measure overturning moments. “There is a correlation between power output and overturning moment, and wind speed and overturning moment. We can accurately measure that on our wind turbine,” he says.

Milliren says his job is to keep the site running – research ready, he says – for new projects. “Ongoing projects include one on wind-turbine acoustic noise, to better quantify the audible range and whether or not infrasound has an effect on humans. Another project is researching advanced, individual blade controls and ways to minimize wakes for the downwind turbines in wind farms."

Wind-turbine foundations are another area of research. “A project starting soon will monitor tower and foundation conditions with an easily deployable, low-cost system to assess the health of a wind turbine foundation.” There is often concern about degrading foundation structural health after a severe storm or when soil conditions differ from expected.

It is a great advantage to wind-turbine owners and operators to be able to determine whether a foundation still meets OEM requirements years after installation.

Even though the Clipper’s foundation is massive – concrete from 45 trucks and 44 tons of rebar – it moves. A sufficiently sensitive tilt meter can detect small amounts of rotation. Measurements of the strain gauges and tilt meter are made by two Campbell Scientific dataloggers.

Contact Milliren regarding research possibilities at milli079@umn.edu. W

www.windpowerengineering.com

AUGUST 2016

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Ask us what options Castrol has for you.

Learn more at Castrol.com/windenergy or 1-877-641-1600.

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UK consulting firm ready to assist wind-farm development DATA IS KING in securing the financing for a new wind farm. Ideally, a developer needs two to three years of wind measurements from several met masts on site, along with data from a lidar unit that has been moved about the site.

That was one message from OST Energy Director-Wind Nick Fleming. “That amount of wind data would be ideal. But we have also learned it is possible to generate assessments with relatively poor data. All available data adds significant value. It is possible to bridge the gap when the full picture is not available, and make good judgement calls on what uncertainties exist at a particular site,” he says.

It is possible to bridge the gap when the full picture is not available, and make good judgement calls on what uncertainties exist at a particular site.

OST Energy is a technical consultancy firm headquartered in the UK. Fleming said the company’s expansion plan is to diversify geographically and technically. “Our ambitions in the U.S. are built on our global experiences, so we are seeing similar issues and technicalities. A couple of things we see in

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www.windpowerengineering.com

the U.S. are transmission and connection issues. They are a global challenge for the wind industry whether projects are in Oklahoma or India. Projects are all driven by the offtake of power while finance issues are common to most projects.”

On the finance side, Fleming says his firm is familiar with complex finance structures in the U.S. “For instance, the P99, a calculated certainty for project success, has become absolutely critical to financing. A sophisticated and reliable uncertainty analysis also supports the requirement of lenders,” he adds.

As for trends, Fleming see that turbines are getting more sophisticated so they’re able to operate in either current leading voltage or current lagging voltage mode assisting with local network voltage control or low voltage ride through issues.

“We are seeing in the U.K. that when storage technology is tapped for service, it is mostly for frequency re-

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sponse. And that knowledge will have application in the U.S. as well. We are trying to bring knowledge from different parts of the world when and where it applies.”

Regarding wind-farm development, Fleming says several problems crop up frequently. “The one we always see on the analysis side is a lack of sufficient data. It is expensive to have all the data-collection equipment at a potential site but it really does make a significant difference when asking for financing on a P90 or P95 value. So the more data, the better.”

Fleming said the number of met masts should be representative of the terrain and it must collect data long term, at least two years ideally, particularly when there are limited correlation data sets from trustworthy and nearby facilities. “Nearby airfields and weather stations are useful. Even tapping into operational data from nearby projects can add value to an assessment. Lidar makes it possible to deploy short-term measurements around the site, so rather than having to employ mobile masts, a lidar campaign should move around the site collecting wind data in three to six-month intervals.

Another key oversight would be turbine selection. “I would advise against the lowest cost turbine because the devil is in the details of the purchase contract. You have to drill into the warranties and into the O&M capability for the OEM’s available support. If you are not going to use the equipment OEM technicians to maintain the plant, you need to know of the experience of the third parties in your area,” he added.

What's more, turbines are improving fast.

“If you make an early selection, six to twelve months down the track there may be a better turbine on the market worth getting approval for. We are seeing greater penetration of 3-MW turbines in the U.S. These have been more of the norm in Europe over the last five years. I understand why the 2 and 2.3-MW turbine are widely selected – they are a benchmark. There are lots of them. It’s easy to see how they will be maintained, and they will be delivered sooner to take advantage of the PTC. But I expect more of the 3 and soon 4-MW units, and they will optimize revenue.”

The PTC has alleviated scheduling issues as well. “Not long ago we were putting turbine deliveries on a fast track to fall within PTC timeframes. But the PTC issue has gone away AUGUST 2016

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now with deadlines four years out. Scheduling was a big challenge in the U.S. before when it was renewed in one and two-year spurts. The worst thing now about a wind farm timing is to make a mistake in construction and you have to fix it during operation. The best projects are those where the plan was systematic, well thought through, and not in conflict with contractors,” says Fleming.

One thing, he says as a consultant, that must be conveyed is that the project works for owners and lenders. “Owner engineers have a particular project perspective. They are trying to resolve issues that have many shades of grey keeping the project on track and doing deals with contractors to make things happen. As a consultant, you learn about genuine construction risks. If you look at this as cold black and white, as a lenders’ engineer, then it is all about risk and risk management,” says Fleming. “It’s not always a realistic perspective so you can say this risk is high, but you still have to ask ‘how is it high?’ Is it a cost issue, or a delay to the project? So we try to tie these two elements together. It helps when both parties have this information so we can say to developers: ‘These are what the lenders are looking for.’ But for lenders, we must

It’s not always a realistic perspective so you can say this risk is high, but you still have to ask ‘how is it high? explain why we occasionally disagree with their lawyers and why we think a particular risk is manageable.”

Most contractors are good when they are not under pressure, adds Fleming. You can talk to one contractor and he will speak with top-string project managers. “But if they are busy and you are onto the second string of contractors, that is when you begin to have issues. It’s true for OEMs. With civil works contractors, electrical contractors, every firm has clear good project managers and good skill sets. And when not under pressure, the projects are fine. But when they are all under pressure that is when you tend to get poor decision making.” W windpowerengineering.com

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What did your job as a wind-resource technician entail?

I was a traveling wind technician throughout the U.S. and Canada, and my job was to find the root cause of serial failures at a wind farm. For example, sometimes more than one turbine at a site had the same part break at almost the same time.

So I would inspect the damaged parts, and all the other turbines on site to see if they were also at risk of failure. Then I would figure out why and how to correct it. Most importantly, I would report back to the manufacturing department to make sure they prevented it from happening on new turbines.

Ask a wind tech: Auston Van Slyke OVER 25 WIND-TURBINE TECHNICIAN SCHOOLS serve the United States today.

But half-a-dozen years ago, there was no such thing as technical training for wind power. Auston Van Slyke knows this all too well. When he was first recruited as a resource technician by Vestas (after life as a Staff Sergeant in the Marines), formal wind tech training did not exist. At the time, he performed turbine repairs that had never before been attempted and soon became known as a trailblazer in the industry.

Today, Van Slyke is the Program Director for Wind Energy Technology at Ecotech Institute — the first and only college in the U.S. focused entirely on careers in the fields of renewable energy. He is experienced and understands the challenges of finding candidates with the right mix of technical skills for what’s become America’s fastest growing profession. For these reasons, Van Slyke is the focus of this issue’s Ask a wind tech.

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for these jobs means I am helping reduce the cost of operating a wind farm and people’s electric bills.

How has a wind tech's job changed in recent years?

Many turbines are getting elevators or climb assists so climbing is much easier for technicians. The tools have also changed and can fit into tighter places for easier handling.

Plus, today’s turbines are Internetconnected, data-driven, and smarter than ever. So today’s wind techs need to know more about computer programs, Internet protocols, fiber optics, and frequency converters.

What about the work challenged you, and what parts did you most enjoy?

At first the challenge was getting comfortable working at heights, in small spaces, and while swaying in the wind.

After a few weeks those things stopped bothering me and the challenge became to understand the workings of the many different parts in a turbine.

I most enjoyed the unexpected, and not knowing until I got to a turbine what system I would be working on that day. The types of repairs I started on were gearbox replacements and main bearing retrofits. Then, I learned about carbon fiber and fiberglass blade repairs, and blade retrofits.

What are the top lessons you teach your students?

Safety first. Don’t take shortcuts or get lazy with personal protection equipment. Wind techs get a lot of hand injuries that are preventable with gloves and the right tools for the job. Take your time and provide quality work. Turbines are typically not looked at for months at a time. A tech’s attention to detail can save a machine from failing in the middle of the night.

Also, this is a new industry and not everything has been thought of yet.

Wind technicians have the opportunity to improve technology and make changes to manufacturing protocols and user manuals.

What made you decide to transition from a technician to a teacher?

I worked as a wind technician for almost five years before I decided to move into training. I had to hire new technicians and it became immediately apparent to me how hard it was to find someone with the right combination of skills and values to succeed as a wind tech. So I thought, who better to help develop a school for wind-technician training? Granted, I took a huge pay cut but getting people better prepared and educated

Why should someone consider a job as a wind tech?

In America, we are building wind turbines faster than ever before. This is because of the right tax incentives, and growth of manufacturing in the country.

We used to import parts from all over the world to build turbines, but now we are exporting them. In fact, a wind turbine is more made in the USA than is a Harley Davidson. With the right education, working on turbines is a safe and rewarding job that can offer a high level of patriotism and pride. W

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AUGUST 2016

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Chinese wind powered system converts 100 tons of seawater a day into fresh Our thirsty world has problem with an insufficient amount of potable water. A Chinese research effort may have an answer in an off-grid, wind powered, seawaterdesalination system developed by the Jiangsu Academy of Macroeconomic Research. The demo project can produce 100 tons of freshwater per day (about 1,000 gal/hr) from sea water. The system, which consumes 2.1 to 2.4 kWh of electricity for every ton of processed seawater, scales to larger output, and can be powered with electricity from a variety of sources. The next step, says research lead Professor and Dr. Gu WeiDung, is a commercial design for converting 10,000 tons of seawater a day. The system was recently announced as winner of the sixth BlueSky Award.

The design produces fresh Redesigning the reverse osmosis water by pushing pressurized seaequipment into a vertical column allows water through a reverse osmosis mounting it inside a turbine tower at module. Dr. Gu says the system its base. One goal is a sufficiently sized turbine and column to produce 400,000 increases its efficiency by 10 to tons of fresh water per day, says Dr. Gu. 15% over the previous model by means of mechanical energy transfer. The system is said to be easy to install and maintain because it fits entirely inside the lower portion of a wind turbine tower. The Academy says when compared with a traditional membrane desalination system, the design allows an 80% reduction in footprint over traditional membrane desalination systems (it’s tall), a 60% reduction in failure rate, a 40% drop in cost, and a 30% improvement in energy use. Another plus says Dr. Gu, is that all production is localized due to its independently developed technology.

Power to drive the system can come from a variety of sources but is expected to be deployed in coastal locations where winds are plentiful. The latest model, a fifth-generation, uses power from a wind turbine to drive an integrated pressure boost and energy recovery device.

The BlueSky Award for Global Top Investment Scenarios says it and the supporting organizations were assembled to provide guidance on largescale applications of renewable energy in developing countries in a move to ease conventional fossil fuel shortages and mitigate the impact of greenhouse gas emissions on global climate. W 20

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TOP: To your health! Professor and Dr. Gu WeiDong (middle) an associates toast their success with water from their wind powered desalination equipment. Project plans include a bottling plant for wider distribution.

BOTTOM: The demonstration base of the Nongrid Wind Power Water Desalination System draws power from several wind turbines and boasts of 100 tons of freshwater/day.

www.windpowerengineering.com

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Wind work around North America U.S. wind industry activity approached record levels in the second quarter of 2016. Over 18,200 MW of wind-power capacity are now under construction or in advanced stages of development, according to AWEA. Utilities and other purchasers are locking in prices at record lows by starting construction this year to qualify for the full-value of the production tax credits. State and city renewable policies are also supporting wind energy. New York approved a Clean Energy Standard that mandates 50% renewables by 2030. Salt Lake City has committed to 100% renewable sources by 2032. And, the Massachusetts State Legislature just passed Bill H.4568, which requires big utilities to buy up to 1,600 MW of offshore wind energy.

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Construction of the 200-MW Kingman Wind Energy Center (near Kingman, Kansas) started with a summer celebration. Local landowners, officials, and company representatives came together and even signed a 150-ft turbine blade that will be used in the project.

Governor Sam Brownback celebrated with a commitment of 50% renewables in Kansas by the time he leaves office in 2018.

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Starr County successfully powered by wind

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The 426th turbine of the Los Vientos’ windpower projects is now spinning near the Rio Grande in Starr County, Texas. It marks the completion of Los Vientos IV, the last of five area projects to begin operation.

It also marks a milestone for Duke Energy Renewables, which has installed more than 1,500 MW of wind energy in Texas alone — more than double its wind capacity in other states combined.

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American-manufactured wind farm helps power data in Indiana

Pattern Energy Group recently celebrated the dedication of the 150MW Amazon Wind Farm Fowler Ridge in Benton County, Indiana. The wind farm consists of 65 Siemens 2.3-MW turbines with ‘Made in America’ components.

The turbine blades, nacelles, towers, and transformers were all manufactured in the U.S. The energy generated helps Amazon Web Services power its data centers.

The project is also expected to add $45 million to the economy over 25 years.

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Senvion installs Canada’s first 3-MW turbine

Senvion installed its first 3-MW wind turbine in North America, the Senvion 3.2M114. It is the first of 46 turbines to be installed at the Mesgi’g Ugju’s’n Wind Farm in Quebec, Canada. The machine has been in service in Europe since 2012, but has been adapted for North American climates. It is equipped with a hot air, anti-icing system to produce maximum yield even in harsh climates.

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Kansas kicks off construction of Kingman Wind

TRC supports Plains & Eastern Clean Line

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U.S. offshore wind one step closer to reality

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The Maine Department of Environmental Protection is working on a new Site Law rule that will address development standards for wind projects. As currently drafted, the new rule will apply to any grid-scale wind energy development that is proposed for location within an expedited permitting area. Under the Maine Wind Energy Act, such developments must be reviewed for impacts related to scenic character, shadow flicker, public safety, tangible benefits, and decommissioning.

TRC Companies has been awarded a $12 million contract by Clean Line Energy to provide land acquisition services, survey permissions, and overall project management for the Plains & Eastern Clean Line transmission project. Clean Line is one of the largest clean energy infrastructure projects in the U.S. It will provide a pathway for 4,000 MW of lowcost wind power, delivered from Oklahoma to the mid-South and Southeast.

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America’s first offshore wind farm south of Block Island, RI is one step closer to completion. At of press time, only one tower section was left to mount before final cabling takes place. National Grid completed the installation of the sea2shore submarine cable connection in June. GE’s Haliade 150-6MW turbines have also arrived on site, ready for install.

GE technicians will then commission the turbines, which will take several months.

windpowerengineering.com

Maine develops new wind-farm standards

Minnesota Power seeks proposals for large-scale wind

Minnesota Power has released the first in a series of Requests for Proposals (RFP) as part of the company’s EnergyForward strategy. EnergyForward calls for a diversified power supply to meet customers’ needs reliably, cost effectively, and in an environmentally responsible manner. In this initial RFP, Minnesota Power is looking for up to 300 MW of new wind generation (in addition to the 625 MW it already has on its system).

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COND I T ION MONITORING

N i c h o l a s Wa t e r s Bachmann Electronic Corp

A word about sensor selection for condition-monitoring systems

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hen I talk to a customer for the first time about conditionmonitoring systems (CMS), I like to get an idea of their familiarity with the technology by asking how much they know about it.

Most engineers respond with some reference to the Fast Fourier Transform (FFT) or the frequency spectrum. For those unfamiliar with FFT, this is a tool that converts raw vibration signals from the time domain to the frequency domain where most of the analysis or diagnostics takes place.

For a customer to mention the frequency spectrum – one of the more challenging hurdles to clear on the path to understanding vibrations for machine diagnostics – tells that the predictive-maintenance community has made huge progress towards educating wind professionals on CMS.

analysis isn’t enough to make an informed decision about which CMS option is right for their fleet. This is because condition monitoring starts with the sensors and ends with the analysis. The quality of vibration analysis has an asymptotic relationship with the quality of the sensor data because the analysis can only be as good as the data it relies on. To avoid putting the cart before the horse so to speak, the conversation should actually start with, “How much do you know about accelerometers?”

A fundamental truth that comes with all rotating machinery is that whether the machinery is deemed “healthy” or on its last leg, it vibrates. Interactions between components that make up the turbine drivetrain cause vibrations to propagate through the structure, contributing to the overall vibrational signature of the system. As vibrations travel

For those in the market for a CMS for their turbines, whether installed as a retrofit project or factory installed by the OEM, understanding the basic analysis isn’t enough to make an informed decision about which CMS option is right for their fleet.

For those in the market for a CMS for their turbines, whether installed as a retrofit project or factory installed by the OEM, understanding the basic 22

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through the structure, they are influenced by the shape and material of the components they pass through, as well as by their collision with incoming vibrations.

Bachmann’s Matthew Mays and colleague install CMS on a wind turbine.

The goal of each CMS system is then to separate each vibration source and analyze each source independently of what’s going on throughout the rest of the machine.

Proper sensor selection comes into play when separating vibrational signatures that are close in fre-quency or boosting low-amplitude signals over the background noise of the system.

There are two types of accelerometers that make up a CMS package: high-frequency accelerometers and low-frequency versions. Their sensitivity is also a consideration.

Sensitivity is a measurement of electrical output per mechanical excitation and is reported as mV/g (sometimes pC/g). For wind-turbine applications, a typical high-frequency accelerometer will have a sensitivity of 100 mV/g and is capable of measuring up to 80g.

www.windpowerengineering.com

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CONDITION MONITORING

The µbridge sensor is a proprietary low-frequency sensor for the early detection of faults on the main bearing.

High-frequency sensors monitor the high-speed section of a drivetrain (helical stage and generator) where defects produce clear and distinct peaks above the noise floor, making detection relatively easy. Defects that appear in the high-speed section produce a lot of energy and reduce the need for extremely sensi-tive sensors. To detect faults in the high-speed section, a sensor must measure higher amplitude signals without overloading the sensor.

Low-frequency accelerometers typically have a sensitivity of 500 mV/g (some vendors will list 250 mV/g and 350 mV/g as low-frequency accelerometers) and are capable of measuring up to 10g. The lowfrequency accelerometer provides increased sensitivity for detecting defects in slow rotating components.

Defects in the low-speed section of the drivetrain are difficult to detect because of the slow rotational speeds of components. This results in low-amplitude excitations caused by the defects. The 100mV/g accelerometer provides a high-level over-view or big picture of what is going on whereas the 500 mV/g accelerometer provides a closer look at the lowfrequency vibration data, giving increased visibility into a smaller portion of the spectrum. The 500-mV/g accelerometer sacrifices some high-end frequency data, but it increases the low-frequency detection capabilities. To achieve the full potential of a CMS solution, it is pertinent that a CMS option comes with both high and low-frequency accelerometers.

When benchmarking one CMS system against another, it is important to under-stand that not all high or low-frequency accelerometers are the same.

Frequency response provides a frequency range that the sensor operates over, and output tolerances across the frequency range that is either in decibel (dB) or percent. For frequency response, look for sensors with the widest frequency range, the lowest lower-edge frequency, and the tightest tolerances over the specified frequencies (Sensor frequency response graphs some sensor ranges).

At Bachmann, our standard high-frequency accelerometers (BAM100) have a sensitivity of 100 24

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mV/g, are capable of measuring up to 80 g, have a frequency response of 0.5 Hz to 14 kHz (±3 dB), and have an amplitude nonlinearity of 1%. Our standard low-frequency accelerometers (BAM500) have a sensitivity of 500 mV/g, are capable of measuring up to 10 g, have a frequency response of 0.2 Hz to14 kHz (±3 dB), and have an amplitude nonlinearity of 1%.

The frequency response can be reported in multiple frequency intervals with different tolerances reported for each interval. The amplitude linearity specifies the sensor’s deviation from the nominal output over the linear region of the sensor’s output. It is especially important for a low-frequency accelerometer to have a low value for the lower-edge frequency and a tight tolerance to increase the ability to detect faults within the slowspeed section of the drivetrain.

Another point worth mentioning is the use of triaxial instead of singleaxis accelerometers in sensors.

Although obtaining vibrations in all three axes is taught as one of the fundamentals of vibration-based condition monitoring, in practice this is not typically implemented because of cost and sensitivity. In a wind-turbine specifically, frequency response marks the difference between a narrowly caught pending failure and a fault missed altogether. Standard triaxial sensors have a lower-edge frequency of 2 Hz, meaning they don’t typically per-form as well in a low-frequency range compared to standard singleaxis accelerometers. In addition, triaxial accelerometers only report about 80% of the signal strength in the two axes normal to the mounting axis. A few CMS vendors provide CMS

units capable of achieving a 99%plus detection rate throughout the drivetrain without the use of triaxial accelerometers, so the added cost of a triaxial is not worth the purchase.

In summary, when selecting the right CMS for a fleet, make sure the system consists of a combination of: • • •

•

Low frequency (for low-speed components).

High-frequency accelerometers (for high-speed components).

Sensors that have a broad frequency response range with a small value for the lower-edge frequency.

Low deviations in their reported amplitude linearity.

Unless cost is not an issue, go with a system that uses single-axis accelerome-ters. Lastly, be prepared to answer the question: How much do you know about accelerometers? W

www.windpowerengineering.com

The BAM100 (high frequency) and BAM500 (low frequency) acceleration sensors come in a durable insulated housing, hermetic sealed for demanding ambient conditions.

AUGUST 2016

8/22/16 8:06 PM

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8/22/16 5:27 PM

RE TR O F I TS

Dave Karpenske CEO P C N Te c h n o l o g y w w w . p c n t e c h n o l o g y. c o m

New ideas for retrofitting turbine communication networks

T

here has been much discussion over the last few years regarding life-extension strategies for wind turbines approaching the end of their 20-year design life. Many ideas involve auditing and restoring gearboxes, or replacing and upgrading turbine components.

These are important concepts, but what’s typically missing from these discussions is attention to the modernization of the systems’ control and communication networks between turbines and their related infrastructure. Most likely this is because of time and costs constraints. It is a daunting task to rip, replace, and re-install new cabling (structured or fiber) typically needed to achieve the necessary bandwidth performance. Never mind dealing with the impact these upgrades would have on the communication slip rings.

Slip rings are commonly used in turbines to transmit electrical signals from a stationary nacelle to the rotating hub.

Chances are they will also need upgrading at some point to effectively support broadband IP protocols.

The cost of retrofitting a standing turbine with new wiring can prohibit upgrade strategies until the network goes down.

Moreover, many older systems were simply not designed to mitigate the electromagnetic or radio-frequency noise in a turbine that can have a performance impact on Ethernet signaling.

These factors lend to barriers that have up until now, made upgrading a turbine’s network to support new sensors, along with control and automation systems, a difficult proposition for many turbine owners and operators. However, there is reason for the wind industry to find ways to take advantage of proactive maintenance as condition monitoring and data collection systems become increasingly more common.

At the control and communication network level, there have been attempts to implement new communication technologies into wind turbines over the last few years to facilitate the repurposing of UTP or unshielded twisted-pair wiring into broadband channels (such as VDSL, or very-high-bit-rate digital subscriber lines). Unfortunately, these communication technologies have not done well in the noise environment present in turbine applications, especially when attempting to communicate across rotating serial slip rings.

Another approach considered for use in turbine networks is wireless communication. But once again, the noise issues within the nacelle and non-deterministic latencies or delays inherent with wireless technologies, has made it a poor choice for turbine use to date.

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A new method now available promises to cost-effectively address network issues at wind farms and provide an upgrade path to improve turbine performance and cost of operation. This technology is already getting deployed throughout the industrial process and control automation markets, and has recently been introduced to wind-turbine applications.

The new “InterMax” technology supports communication and control system upgrades to Ethernet protocols by using original serial wiring and slip rings in the turbine design.

InterMax products from PCN Technology provides turbine operators the capability of repurposing existing wiring to facilitate deployment of ethernet networks by reusing all of the existing cabling currently in operation.

Here are four application use cases for use in wind turbines.

PCN Technology’s InterMax products provide advanced repurposing technology for deployment of industrial Ethernet-based networks, including those used in wind turbines. InterMax products do not degrade the performance of existing automation wiring or networks.

www.windpowerengineering.com

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we are keep it simple people We know you are looking for solutions, not just sensors. Complete retrofit kits, tailored to your turbine make and model, enable you to easily transition from your previous sensor to the Hybrid XT. Engineered exclusively for the wind energy industry, these turbine control sensors offer all-weather performance and durability for increased turbine uptime. All backed by our lifetime technical support and 2-year warranty.

Reliable, rugged equipment. Easy installation. It’s what we do best.

www.renewablenrgsystems.com

Henry Bush

RNRG Senior Test Engineer

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8/22/16 5:34 PM

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1. Full repurposing of legacy serial wiring to transport Ethernet protocols (including Ethernet, Profinet, Modbus TCP IP, and others) At some point in its lifetime, there is a need to upgrade a wind turbine’s control and communications networks from older serial (RS-485) technology to operate IP or Internet protocols such as Ethernet, Profinet, and Ethernet I/P. Typically, this would require the time-consuming job of ripping out and replacing the legacy or older wiring with new structured cabling. Now it is possible to repurpose the legacy two-wire twisted pair wiring to carry a new desired IP protocol when using InterMax products.

This option works well for field upgrades, and supports multi-drop topologies and 100BASE-T (a common Ethernet standard that supports data transfer rates up to 100 megabits per second). It also saves time, costs, and the complexity of planning and implementing a full wiring upgrade.

The repurposed wire can also inherently work in extreme noise environments and operate broadband signaling over unshielded two-wire networks, making it ideal for use in wind turbines.

2. Maintain legacy serial communications while adding Ethernet (new features) onto the same wiring Several upgrade scenarios make it necessary to continue operating the legacy serial communications and control applications in a turbine, while adding select IP sensors and functions.

Ultimately, both protocols (serial and Ethernet) must operate simultaneously during the process.

Until now, it has not been possible to operate both protocols on the same wiring at the same time. This issue is compounded by a need to communicate the serial and Ethernet protocols over a legacy serial-communications slip ring.

However, with a new "dual protocol" communication capability, 28

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RETROFITS

Placing communication units for a network upgrade

PCN Technology’s InterMax units support the retrofit old wiring in a turbine. The products provide industrial network operators with the capability of repurposing their existing wiring by reusing all of the cabling currently in operation.

it is now possible to repurpose the two-wire network to communicate IP (Ethernet) and simultaneously and asynchronously communicate the legacy serial traffic over the same twowire network — while communicating through serial slip-ring channels.

This means an older wind turbine can add IP functions and not disrupt its serial technology operating at the same time. Therefore, it is possible to add new networking capabilities that improve performance and reliability in a turbine while maintaining its old system. This extends the life of older turbine systems.

Such an upgrade supports up to 128k baud serial (the speed of communication), and simultaneously and asynchronously supports 100BASE-T packet protocols.

3. Install wiring in series with any slip ring (except optical), and measure brush wear and material deposition on the pads With advanced InterMax signaling technology, it is possible to measure and store signal-to-noise (s/n) ratios.

The measurement of noise values is fundamental to how PCN Technology establishes encoding FFTs (Fast Fourier Transforms) and decoding IFFTs (Inverse FFTs) to maximize the bit rates per carrier AUGUST 2016

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(OFDM scheme), or orthogonal frequencydivision multiplexing, being a method of encoding digital data on multiple carrier frequencies. FFTs are DSP algorithms that convert signal data from the time domain to a more useful frequency domain. The IFFT does the opposite.

Unlike conventional DSL (Digital Subscriber Line) used for high data bandwidths, this approach re-measures the signal-to-noise ratio and re-establishes encoding and decoding values every few milliseconds. This is why it is possible to receive such high bandwidth speeds through old, noisy two-wire networks and operate smoothly through the spurious noise of slip rings.

Where DSL makes an initial measurement for encoding and decoding at power-up, InterMax technology makes continuous measurements every few milliseconds, and modifies the FFT and IFFTs to adjust each carrier for intermittent and sporadic noise changes.

Perhaps most importantly, these signalto-noise values are captured and stored.

This provides an opportunity for analysis and review of how well a slip ring is performing over its serial or IP communications path.

Analysis of these signal-to-noise values also means it is possible to determine

the condition of the brushes and material deposition on the pads.

By developing signal-to-noise system profiles (templates), an operator can determine when communications will begin to fail and use data as a predictive tool for servicing slip rings.

4. Implementing new cabling to a system with IP infrastructure There is value in using InterMax technology for turbine control and communications even when an IP slip ring and structured cabling is already in use.

This scenario applies to new factory builds and field upgrades because the problems of brush wear and material deposition still occur in IP slip rings.

Benefit of upgrading an existing Ethernet path through a slip ring include in-situ slip ring condition measurement and frequency modulation signaling with constant adjustments. This means communication can continue to operate even when a slip ring’s brush or pad connection has degraded to the point of becoming capacitive coupled. It is then possible to communicate across a degraded slip ring well after normal Ethernet devices stop working or reach failure mode.

This ability extends the usable time between service calls, saving a technician’s travel and repair time, and other related costs. Additionally, a new IP technology turbine with InterMax wiring could use a lower cost serial slip ring for communications. By retrofitting wiring in wind turbines, it is possible to enhance communication and improve turbine performance. W

windpowerengineering.com

WINDPOWER ENGINEERING & DEVELOPMENT

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B O LT I NG Daniel Provost O w n e r, N e w W o r l d Te c h n o l o g i e s

Think calibrations to keep bolting tools accurate

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he objective for calibrating a torque tool is to ensure that it applies the torque the tool indicates it is applying.

Transducers – the sensors used to measure torque applied by the tools – come in many different sizes and torque ranges. Those most commonly available for the wind industry have 0.5 to 1.5-in. square drives and torque ranges from 100 to 10,000 ft-lbs.

For instance, a conventional clicktype torque wrench typically uses a handle with engraved markings that are rotated to align with the incremental values on the shaft of the wrench.

Compressing a mechanical spring and cam produces an audible click at the indicated specific torque value Hydraulic torque wrenches require a calibration process, which usually involves two tiers. The first verifies the actual torque output of the hydraulic tool. This is done by gradually increasing the hydraulic pressure to the tool while it is on the calibration stand and connected to a static digital read out transducer. The calibration technician will verify the torque output from the transducer and compare it to a precision hydraulic-pressure test gage.

In the second tier, the hydraulic pressure gage on the pump that accompanies the wrench is removed and tested against a precision-calibrated test gage.

Torque up to 1,500 ft-lb is classified to BS 7882:2008 as Class 1 or better for the primary range (±0.5% of reading from 20 to 100% of full scale). From 1,400 to 7,000 ft-lb is classified to BS 7882:2008 as Class 0.5 or better for the primary range (±0.25 % of reading from 20 to 100% of full scale) benches. When the pump gage is not reading properly, it should be changed out.

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The RAD Transducer Series comes in torque ranges up to 7,000 ftlbs along with a calibration certificate from an ISO 17025 accredited lab.

Electronic torque-wrench calibration differs from the static testing of hydraulic wrenches. Electronic gear-reduction tools must be tested and calibrated dynamically. Electronic tools deliver constant rotational drive right up to final torque, unlike hydraulic versions which rotate at 25° per activated stroke.

The calibration equipment needed includes a calibration stand to hold the transducer and dynamic rundown fixture.

The stand must be able to carry the high reactionary forces produced by the tool.

Qualified technicians calibrate electronic tools by comparing the digital readout on the tool to the actual readout from the transducer. When they are not within tolerances a technician can adjust the calibration angle in the tool which is

Aside from static transducers, the company also manufactures the RAD Smart Socket which allows for field calibration on a live application – on the job.

www.windpowerengineering.com

AUGUST 2016

8/22/16 8:16 PM

B O LT I N G

The RAD 1500 Transducer Systems allows calibrating torque wrenches and those with ratings up to 1,500 ft.lbs.

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based on a percentage of current drawn for that torque value.

The period between recalibrations differs from manufacturer to manufacturer. In most cases, the period would be one year after initial factory calibration. Electronic torque tools may have a cycle counter built into the software which can be set to alert the operator that a calibration or re-torque is due. In many cases, re-torquing can be done in the field making it unnecessary to dispatch the tool to a service center.

Calibration transducers should also be re-calibrated on a regular basis.

This process can be done by accreted laboratories (usually ISO 17025) that would be equipped with certified test beam and weights. RAD Transducers are classified to BS 7882: 2008 or better for the primary range (±0.5% of reading from 20 to 100% of full scale) New World Technologies (manufacturer of the RAD Torque Systems) has been building and calibrating gear reduction torque wrenches for over 20 years. The company considers calibration of all its tools (pneumatic, battery, and electronic) critical to their performance and accuracy.

Over the years the company has used transducer from various manufacturers in an attempt to find a best system for its gear reduction drive tools. In 2013 the company began manufacturing transducers in house for the tools it produces. W WINDPOWER ENGINEERING & DEVELOPMENT

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TOOLS AND SERVICES TO GET THE JOB DONE

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PR OJ E CTS — T RA NSM I SS ION

Prior to securing land for a new wind development, it is important to research the local infrastructure including current transmission system operation, long-range plans, and proposed system upgrades for that region.

W

ind-farm development is a complex process. As a new wind project progresses through various stages of development, there are many opportunities for mistakes that can seriously affect its final outcome and success. Some of the biggest mistakes begin early in the development process, and are difficult to overcome as a project progresses.

Poor site selection is all too common with new developers. Sites are chosen for the wrong reasons, such as location preferences or without sufficient due diligence. They are also ill chosen for lack of consideration of the grid or transmission capabilities.

Transmission lines may be located near a potential new windfarm site, but gaining access to these lines is another matter that can prove challenging and costly. There have been plenty of new developers who’ve secured a project site and permits only to find out nearby transmission lines cannot carry more load. Ensuring that a site is ideal for a new wind farm includes asking important questions related to the grid, such as: • • • • •

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What transmission lines are nearby, and what is their available capacity?

How accessible is the grid, and have other developers showed interest in gaining access to the transmission in the area?

What transmission upgrades (and costs) are necessary to accommodate a new wind project?

Who will buy the wind power once connected to the grid?

If planning to sell to a local utility, can the power get delivered directly using nearby lines or are multiple systems required for power delivery?

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Jay Haley PE, Principal in Charge EAPC Wind Energy

A wind developer’s guide to the transmission grid This is the second in a two-part series on wind-farm development. The first article, entitled Advice for firsttime developers, was published in the June 2016 issue. It discussed some of the regulations and challenges of windfarm site selection. While many developers put time and consideration into new project siting, permitting, turbine selection, and financing, transmission is sometimes an afterthought. However, transmission considerations are just as important as finding the right project site. Here’s why.

Wind developers should consider answers to these and other questions carefully as part of a successful project development process.

Understanding the grid A transmission grid is one of the most complicated engineering systems devised by man. It is complicated technically in terms of how electrons flow from generators to the load (or end user), and contractually in terms of how costs are allocated. The process of gaining access to the transmission system is also complicated and costly.

Much like securing a project site, when developing a new wind farm it is imperative to conduct similar due diligence on the local transmission system. Research the local infrastructure

Some of the biggest mistakes in wind development begin in the early stages and are difficult to overcome as a project progresses.

www.windpowerengineering.com

AUGUST 2016

8/22/16 8:18 PM

PROJECTS — TRANSMISSION

and look into proposed upgrades to transmission systems and substations. Also consider potential long-range plans for large transmission projects and the overall system operations for the region.

Here is a step-by-step guide for getting your new wind project connected to the grid. Although this process will vary from one system operator to the next, the general steps are similar.

1. The interconnection request You have located what seems an ideal site for a new wind farm and may have already started a wind-resource assessment campaign. Next, it is time to ensure the power produced by turbines can efficiently and cost-effectively find its way to electricity users. This process typically starts with an interconnection request. Your position in the queue (other interested developers are often in the area) is determined by the date of the request, and receipt of a non-refundable prepayment for a feasibility study.

2. The feasibility study This study is generally required to assess the viability of the transmission lines and capacity for the proposed project. Its purpose is to determine with minimal effort, time, and cost whether there is a reasonable likelihood that the interconnection request can be satisfied. Remember to set aside resources for this process.

The cost of a study is typically in the range of $5,000 to $50,000. This range reflects the size of the project scope, grid access, and number of transmission lines in the area. The study itself does not usually take long and, on average, completes in less than a month. However, this is dependent on the number of study requests in the queue and it could take a year before your study request makes it to the front of the line.

3. System impact study If a feasibility study is given the green light and the interconnection request accepted, the next step involves a system impact study. Note, this step will cost more and take longer to complete. The typical cost could range from $20,000 to over AUGUST 2016

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$100,000, depending on the size of the wind farm. And expect it to take up to six months or longer to complete once your request has made it to the front of the queue (this could also take a year or longer).

As its name implies, the purpose of a system impact study is to consider the potential system impacts that may affect local transmission lines and the overall grid from injection of new wind energy from your project. Essentially, this study will determine: •

•

•

The minimum amount of interconnection service available for the proposed new wind project — without the need for system upgrades.

When upgrades or reinforcements are necessary to handle your request, the study will provide a detailed list of the upgrades including a highlevel cost estimate for them.

A rough timetable for when transmission access could be granted.

To properly complete a system impact study, it is necessary to have detailed information about the exact wind turbines planned for your project. If you didn’t start your windmonitoring campaign early enough, you may not yet have enough information to choose an ideal turbine make and model for the site. In this case, you will have to wait until the wind assessment is complete, potentially wasting time and your place in the queue, so plan accordingly.

4. The facilities study If you’ve managed to successfully make it through steps two and three, the next stage involves a detailed facilities study. This study is quite involved and will help determine what equipment is needed to reinforce the grid to accommodate your project. A facilities study provides developers, utilities, and transmission owners and operators with a precise list of upgrades, costs, and timetables for interconnection and improvements if necessary. It also tells when you’re able to gain access to the transmission system. Typical costs for this study range from $50,000 to over $100,000, and could take six months to a year to complete.

5. The transmission service request If your proposed wind-farm project makes it through to this point and has proven technically and financially feasible from a grid standpoint, you are now in a position to make a formal transmission service request.

This request is for the right to use a specific amount of capacity on the grid to deliver wind-generated power from one location to another. It is a good sign and means your wind project is ready to go, at least from a transmission viewpoint. However, it won’t come cheap.

Expect to make a substantial payment for this service, possibly hundreds of thousands of dollars.

Wind development is certainly not for the faint of heart. As mentioned in Part 1 of this series, if you intend to sell power to a local utility once the wind farm is up and running, it is a good idea to open up a dialog early on and maintain realistic expectations about anticipated power pricing. Many potential transmission-related risks may crop up along the way. Seeking winddevelopment advice from experts in the field can help avoid pitfalls that could derail a project. W

The 34.5-MW Munnsville Wind Farm in New York is an example of a successfully developed wind project.

It has been generating power for a number of years and consists of 23 GE Energy 1.5 XLE wind turbines.

Photo: EAPC’s Bob Sherwin.

windpowerengineering.com

WINDPOWER ENGINEERING & DEVELOPMENT

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CABL ES

Uwe Schenk Global Segment Manager – Wind HELUKABEL w w w. h e l u k a b e l . c o m

New standards favor UL-listed cables for wind turbines

U

nderwriters Laboratories is a global independent consulting and science company dedicated to product safety. A product with a UL listing ensures that it is in compliance with local safety standards.

Wind turbines have recently come under scrutiny in UL 6141 and UL 6142. These are the first American safety standards developed specifically for wind turbines. These UL standards simplify the approval process for wind-turbine electrical systems and cables through local Authorities Having Jurisdiction (AHJ) inspectors.

In the U.S., AHJs must certify that products are safe to use in accordance with general American installation regulations such as NEC, NESC, and ANSI/IEEE C2, among others. It is not always clear whether components that comply with European CE standards also comply with American installation regulations.

If there is doubt, an AHJ inspector may completely shutdown a construction project.

UL 6141 and UL 6142 were formulated to provide a set of rules that help inspectors with the approval process, making it more transparent and predictable for everyone involved.

TOP: The HELUWIND WK DLO 2kV-Torsion is a flexible power cable specifically for use in wind turbines with outputs up to a nominal 2 kV. It is engineered to withstand the rigorous demands of torsion applications in turbines, such as the cable loop.

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Why did North America introduce its own turbine standards?

For years, there were no national safety standards specific to wind turbines in North America. The only guideline AHJs had for reference was the International Electrical Commission (IEC) 61400, which is the international standard for electrotechnology in wind turbines.

The IEC standard was never well received, however, and has been criticized in North America for lack of clarity and information. Critics claimed that it did not include enough provisions regarding electrical safety of components, controls, or protection devices.

UL has since developed national standards to supplement IEC 61400. These standards refer directly to IEC 61400-1 (Design Requirements) and IEC 61400-2 (Small Wind Turbines). They also add technical requirements regarding the safety of electrical, control, and fire protection devices in wind turbines. Essentially, the UL standards help bridge the gap between IEC standards and requirements set by national installation regulations.

American National Standards Institute (ANSI) has recognized UL 6142 (Small Wind-Turbine Systems) as a national standard since 2012. It applies to small turbines, those with a nominal output capacity up to 1,500 Vac that cannot or should not be entered by operators or service technicians for operation or maintenance.

In May 2016, ANSI issued UL 6141 (Standard for Wind Turbines Permitting Entry of Personnel) as an American National Standard. UL 6141 applies to large turbines that can

BOTTOM: The new HELUKABEL TRAY X is a flexible control power cable with cross-linked polyethylene (XLPE) insulation. Rated for up to 600 V (WTTC 1000 V), these cables are suitable for all wind-turbine cable tray applications.

www.windpowerengineering.com

AUGUST 2016

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CABLES

or may be entered by operators or service technicians for operation or maintenance. Both UL standards apply exclusively to onshore turbines.

These recent safety standards only effect new construction or refurbishing of wind turbines with a capacity greater than 500 kW. Existing systems need not be refitted.

How does UL 6141 impact the use of cables?

UL 6141 focuses primarily on electrical safety and introduces several restrictions on cable use in the future. The bottom line: appliance wiring material (AWM), or cabling material that is not UL listed, may only be used minimally.

Until now, AWM cables were frequently used in wind turbines. UL 6141 stipulates that: All accessible cables need to be installed in cable ducts. If this is impractical or impossible (e.g. in the cable loop, only so-called tray cables — cables that are approved for exposed run) are allowed. Cables in the tower and nacelle are usually accessible and, therefore, have to be certified for exposed run as well.

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Unlisted AWM cables may no longer be used for exposed runs. Tray cables designed for use as exposed run cables that are oil and flameresistant fulfill the increased safety requirements of UL 6141. In fact, cables must now hold the UL listing to meet classification as tray cables.

Other UL standards are already in place to regulate components, such as generators, in certain wind-turbine subsystems. These standards continue to apply. UL 6141 will apply to areas that were not previously regulated by a standard.

Local AHJ inspectors already favored ULlisted components because the certification helps standardize and accelerate approval processes. Recognition of UL 6141 as the national safety standard for American markets will make using UL-listed components even more prevalent than before.

Although UL 6141 does not completely rule out the use of AWM cables, it does limit their use to such an extent that UL-listed cable products will likely become the go-to choice for wind turbines. W windpowerengineering.com

Cable performance is critical throughout an entire wind turbine. Two key areas are the nacelle, where cables must withstand exposure to extreme temperatures and lubricants, and the cable loop. Here (right image) cables experience high levels of mechanical stress, such as torsion, from repetitive twisting as the nacelle yaws in daily operation.

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LUBR I CA NTS Michelle Froese Senior Editor Windpower Engineering & Development

Analyzing the lifeblood of wind turbines

I

f wind is breath to turbines, then oil is the lifeblood that keeps these machines running smoothly. And a healthy, well-oiled machine is one that works reliably and for long periods.

It’s not unlike our own bodies, which tend to last and function better with proper care and nourishment. This, according to David DiNunzio, Wind Application Engineer at Castrol, “I compare turbine oil to the blood we have in our body,” he said during a presentation at the American Wind Energy Associations’ WINDPOWER 2016 conference and exhibition earlier this year in New Orleans.

“Every year I go to my physician and get a complete physical.

The doctor takes a couple vials of blood, sends it off, and a week or two later I get a report back about my overall health.” So far, there has been nothing to worry about. But just imagine, he said, that one time your blood tests are flagged and read outside the range of “normal.”

You might be told you need immediate surgery or a blood transfusion.

“If it were me, I’d want to have more information before committing to either procedure,” DiNunzio said. “I'd want to dig a little deeper and maybe get more tests to confirm the diagnosis before taking serious action.”

In the wind industry, proper operations and maintenance also requires testing of the “lifeblood” used in turbines. Wind-farm owners or operators often send oil samples out for analysis to established laboratories. Oil properties and contaminants associated with component wear are then routinely assessed to monitor equipment health. Oil loaded with contaminants or wear materials could mean there is a problem with the gearbox.

But what if an oil property falls outside an acceptable “healthy” range? When is immediate action warranted and when is it time to dig

Today there are more options than ever before for treating turbine oil, and chemical adjustments can often be made up-tower to save time and money.

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a little deeper? “You have to recognize that there’s a lot of automation in the analysis process, and that there may be limitations in the test methods,” explained DiNunzio, and he is talking from experience. His team at Castrol tested this statement by sending identical, used turbine oil samples to five different laboratories.

“We did this in triplicate,” he said.

“We sent them into different labs at different times and gathered the data back to compare because we wanted to see what the trends looked like.”

One of the parameters DiNunzio looked at were the results for water measurement levels. “I know this is sometimes a driver for understanding the condition of turbine oil and what type of contaminants are getting in there. But based on the test method and repeatability of that test method, well, there was no firm result. And because we don’t know exactly what each test number was, all we can do is look at relative standard deviation.”

In comparing the different lab results, those numbers were bouncing up and down up by about 30%.

DiNunzio explained that sometimes you can be plus or minus up to about 150ppm of water for this type of measurement but, because there are variables in the testing process, lab results will vary each and every time.

If you’re surprised, don’t be.

“These labs are producing thousands of oil samples every month,” he said.

“And as I mentioned, results are largely automated and based on each lab’s own set of parameters.”

Particle counting provides another example of an automated process. It works by running oil

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through an automatic laser counter, and anything that interrupts that laser light is going to register as “abnormal.”

“The issue: not all particles are wear materials,” DiNunzio said. “Things like air, water, and even some additives can interrupt the laser light and make the oil seem dirty.”

The International Organization for Standardization, or ISO, has developed a code for cleanliness included on most industrial oil analysis reports. The code can help establish targets and determine the overall cleanliness of a monitored system.

“However, as cleanliness standards get tighter and you get bigger in the micron scale, errors can increase quite a bit because there are a lot fewer particles in there. Plus or minus 5, 10, 15 particles can change the cleanliness numbers significantly.”

Another case in point: phosphorus. This is an example of a common additive element and extreme pressure additive indicator. With phosphorus, it is possible to get an accurate reading, at least for the most part. “When we got the phosphorus data back from all the different laboratories, we could see where the numbers fell in relation to what the numbers should have been — at least when using the ICP process.” ICP or Inductively Coupled Plasma is a spectroscopy process used for measuring metallic and chemical elements that lends itself to high accuracy. But when identifying parts per million, or PPM, it is first necessary to have equipment calibrated for that element and for a particular range to ensure a constant level of accuracy.

“It’s like asking whether a ruler or a micrometer is being used to measure something. If your calibration is off for a particular element, results may come back quite different from the value you were expecting.”

A 30% variance in lab results may not seem like much but when it comes to planning for oil changes and proper turbine O&M, these are costly decisions worthy of good logic. “So how much stock are you putting into one particular data point, and what kind of margin for error should you expect?” These are important questions, according to DiNunzio. “Ultimately, we want to use more than one data point and the trending information that leads us down a path that makes the most sense.”

He mentioned that there is also seasonal information to be gained from analyzing data over time. For instance, depending on the time of year, water numbers will go up or down in turbine oil. “It's not uncommon for that to happen,” he said, “and it’s another good reason to look at a wider spread of information rather than one individual data point before making conclusions about your turbine’s oil health.”

If there’s a prime piece of advice DiNunzio can share with wind-farm operators it is to benchmark your data. “Pull samples from your turbines, send one to one lab and one to another lab. I mean it. And expect results to differ. You're never going to get the same numbers back, but you do want to see that they are trending in the same direction.”

Aside from analyzing individual data points, also look at the look at the lab report as a whole. DiNunzio said it’s important to look for trends or interference. “If the particle count is going AUGUST 2016

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Wind-farm owners often send turbine oil samples out for analysis to established laboratories. An oil with excessive contaminants or wear materials could mean there is a problem with the gearbox.

up, check to see if the iron is also going up. And verify if the PQ [particle quantification] index is also on the rise. Basically, you want to see if there are several parameters that are indicating the same thing, or if an out-of-range data point is merely a reflection of a lab’s measurement error.”

It's also a good idea to take a look at the turbine itself. “Make sure the oil sample you’re relying on is worthwhile,” DiNunzio advised. “Think about it: you’re taking a four-ounce sample out of an 80-gallon gearbox and hoping that it is representative of what's seen throughout the whole machine.” So, it’s important that if there is a cause for concern in the oil analysis that it’s verified.

“The analysis is really only a good form of predictive maintenance, but to protect your asset, you probably want to dig a little deeper before you take costly corrective actions.” It’s just like with your own blood results. “Verify before you act,” said DiNunzio.

Fortunately, today there are more cost-effective options than ever before for treating turbine oil, if and when necessary. Chemical adjustments are now often made up-tower and are incredibly cost and time saving. “We’ve gotten creative thinking outside the box in terms of what we can do to improve oil condition up-tower as far as the chemistry goes. It saves from having to take a turbine down and lets technicians focus on other important jobs.”

For instance, treatments are now available that can chemically drive water out of oil and chemicals that can enhance an oil's ability to release entrained air to break up foam.

“One of the latest technologies is an ability to replenish some of those additives that are used up in the normal course of protecting the gearbox. For example, as EP additives work — those are consumables — they also sacrifice themselves, so to speak, to prevent wear. They plate themselves out of those metal surfaces and don't go back into the oil. So we expect to see a gradual decline of additives in oil samples.”

As the lifeblood of a wind turbine, oil can reveal a lot about the health of the gearbox. “And we are making more and more progress because we’re watching the trends and researching advancements,” said DiNunzio. “Today, the potential exists to extend the life of turbine oil from the common five-year life to an additional five years. Maybe even oil for life? That’s a big gain and real material savings worth analyzing.” W windpowerengineering.com

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I NSPE CTI ONS Becki Meadows Consulting Engineer R o m a x Te c h n o l o g y

End-of-warranty best practices: Let data drive the inspections Planning for a wind farm’s end of warranty (EOW) involves a great deal of organization.

A full inspection campaign is costly and not always 100% effective. These campaigns generate mountains of data that can prove challenging to synthesize, which also makes it difficult to fully capture the health of the farm and identify systemic issues. However, stateof-the-art tools and advanced data analysis methods can help owners maximize the benefit from an EOW inspection campaign.

Typical lead times for vibration-detected problems

Data-driven inspections Performing a full vibration sweep prior to the start of an EOW inspection campaign offers many benefits. Vibration analysis can detect almost all cases of significant damage in the wind-turbine drivetrain, including main bearing, planetary-stage gears, intermediate-stage gears and bearings, high-speed stage gears and bearings, and generator stator windings and bearings. When vibration analysis points to a problem at a certain location, a focused inspection can then take place. Additionally, EOW claims may catch components that are missed by an inspection campaign alone, such as: planet bearing damage on inner rows, early stage axial cracking, and ring gear damage below the oil line.

The steps to a successful EOW campaign include: • Start planning the inspection campaign at least 12 months in advance of warranty expiration • Perform vibration analysis to identify damaged main bearings, gearboxes, and generators • Perform drivetrain and tower walk-down inspections • Perform additional vibration analysis close to the EOW date • Perform targeted follow-up inspections prior to submitting claims The recommended EOW process chart relates to typical vibration detection lead times prior to failure.

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Vibration analysis gives notice of the likely arrival times for the problems in the arrow bars.

Source: Romax Technology

Main bearing faults develop slowly over time, but it’s important to replace a bearing before catastrophic failure. Bearing cracks also develop slowly and the gearbox may operate without obvious indications, such as noise or temperature changes, until the cracks fracture the entire bearing race. Alternatively, gear tooth cracks may develop quickly into fractures and, depending on the location, can damage the entire gearbox.

The value of vibration monitoring provides an example where advanced vibration detection algorithms give 17 months of warning prior to a main bearing failure. A wind-farm owner may become

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The value of vibration monitoring

liable for the high cost of its repair when damage is missed through inspection alone. Good practice combines vibration monitoring with targeted follow-up inspections to document damage progression. This data can then help quantify and mitigate an owner’s responsibility for a future failure.

In an EOW monitoring case study, vibration analysis indicated damage on the IMS (intermediate speed) rotor side bearing. The bearing could not undergo inspection because a bearing cover prevented borescope access. However, the vibration trend was clear and matched a historical trend for a turbine that recently had its IMS bearing replaced due to inner race axial cracking. This same trend was observed on five other turbines in the fleet. With this data, an owner can track damage progression with vibration analysis. This, combined with past documentation of the turbine with the replaced IMS bearing, could be used to submit a warranty claim for the issue.

Advanced detection algorithms provided 17 months of warning prior to main bearing failure.

Vibration monitoring, combined with targeted follow-up inspections, documented damage progression.

Flushing extended the bearing life and optimized the cost of the repair.

modes, comments, and ratings to each component based upon this checklist.

Inspections are then uploaded to a Cloud server, which converts the data into a report. The engineering manager can then review the results, compile the data, and generate a punchlist with little to no delay. Additionally, the standardized terminology for issue classification lets users create a useful database to quickly analyze failure data across a wind farm.

Vibration analysis provides significant added value to an EOW inspection campaign. Each main bearing or gearbox with detected damage that is repaired under warranty saves an owner $200,000 to $300,000. Also, using advanced inspection tools can reduce the time and cost it takes to finalize reports and generate effective warranty claims. W

Inspection and reporting tools In the current EOW practice, a large volume of valuable data flows in from the field. A lot of time and money is typically wasted on administrative tasks for reporting and record keeping.

Field Pro, Romax InSight’s mobile inspection and service application, was developed to reduce time in generating highquality inspection reports and to effectively leverage data from an EOW inspection campaign.

Field Pro integrates easily into EOW inspections. Before an inspection, an engineering manager can establish a standardized scope of work by job type, turbine model, and task. In the field, the mobile app lets technicians take pictures and add failure

Inspection data captured in Field Pro is stored in a structured database for the quick analysis of failure data across a farm. In this case, the pitch ram (rod) on two different turbines show the same problem.

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Santhosh Chandrabalan Global Business Manager 3M w w w. 3 M . c o m / w i n d

Best practices for blade protection and repair

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hile generating power, wind-turbine blades must endure a variety of elements such as rain, hail, blowing sand, and salt spray. Blade tips spin through these conditions at up to 200 miles per hour. It is no wonder such conditions cause a fair share of wear and tear on blades, including leading-edge erosion over time. If blades are not properly maintained or protected, they can deteriorate to the point where water erodes the material and threatens a turbine’s performance.

Even minor damage on turbine blades can impact the operational efficiency of a wind farm and lead to a loss of annual energy production and profit. Recent studies have demonstrated

The best maintenance approach to blade erosion is a proactive one.

Studies consistently demonstrate that even minor blade erosion can lead to an AEP loss of at least 4%, and up to 20% in more severe cases.

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that pits and gouges reduce AEP from 4 to 10%.

Delamination, or blades that begin to split or tear, reduces AEP up to 20%.

Unfortunately, leading-edge erosion is a problem that eventually affects all blades, regardless of turbine location, height, or blade length. OEM’s are consistently looking for new preventative measures and repair products that enhance blade reliability and longevity.

Here we review the current products available to the wind industry for optimal blade protection and repair, and suggest best practices for safe and proper application.

Blade-protection tape What is it: Protection tape was originally designed for the heavy-duty use of helicopter blades and aircraft radomes, and is now one of the most recognized and used products for leadingedge erosion maintenance and repair of turbine blades. The tape is constructed from durable, abrasion-resistant polyurethane elastomers that reliably resist erosion, puncture, tearing, and weathering. The composition of the tape also protects blades from pitting, wear, and water damage when applied on the leading edge.

Why use it: Wind protection tape is one of the best options to repair turbine blade damage because of its uniform thickness and finish. While other protective coatings are sometimes affected by environmental conditions, such as humidity and temperature, properly applied tape is not affected by weather conditions.

It can also provide a faster, more efficient application process for blade nicks and damaged edges.

Best practice: Before deciding on a bladeprotection tape, it is important to evaluate each product’s material composition and application instructions. Consider the tape’s UV stability and note if special tools are needed to apply it. Also consider where the application is recommended – either in factory or directly in the field by rope or access platform.

Regardless of location, the surface on which tape is applied during blade repairs can significantly influence the tape’s durability and performance over time. So when repairing a turbine blade with protection tape, it is imperative to first smooth the damaged surface at the blade’s leading edge. This may require more skill and equipment in the field and while several meters up-tower.

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Once debris is removed, repair technicians must determine whether to use a wet or dry application technique.

A wet application process is recommended for long, straight sections of a wind blade.

• •

•

•

First determine the length of tape required based on the blade size (and include a little extra tape).

Align the protection tape to the required area and apply along the top edge, leaving the extra section of tape unused during the process.

Fold the remaining tape back and remove the liner. Spray the application solution included in the wet package on the protection tape and substrate.

Lay the remaining tape in position while applying slight tension. Use a squeegee to remove the application solution from beneath the tape.

A dry application technique is recommended for curved and contoured blade sections.

• •

• •

Cut a narrower section of protection tape using scissors to “neck down” a short section near the blade tip.

First ensure the center of the tape is aligned to the leading edge of the blade.

Then hold the tape at one end of the damaged area, while stretching the tape around the contoured blade section.

Be sure to apply slight tension to the edges of the tape, and use a squeegee to apply the tape to the surface.

If extra tape remains, trim along the edges and press it into place.

Protective coatings What is it: Protective coatings are formulated to maintain the integrity of a blade’s leading edge from sand, rain, debris, and other minor impacts. Coatings are best used as a preventive measure, protecting blades from the elements as soon as turbines are up and running.

Why use it: These polyurethane coatings provide excellent erosion protection in either single or multiple layers, and can apply easily with a brush or casting. Casting involves pouring a coating, letting it flow to cover the product at will, and without use of an application tool.

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Best practice: When selecting a bladeprotection coating, OEM’s should look for one with a fast and efficient curing process that can be used in the factory or field. When the turbine blade has existing damage, products such as fillers, abrasives, or accessories should be used in addition to coatings to ensure a comprehensive repair.

Ideally, this application process is a two-person job.

application, remove the masking tape and let the coating flow to the tapered edges.

Epoxy and polyurethane fillers What is it: Blade manufacturers may use epoxy or polyurethane fillers to fix surface defects or create a smooth transition between blade halves. Fillers technically become the base of a blade’s leading edge, so they significantly influence how that edge resists erosion.

If blades are not properly maintained or protected, they can deteriorate to the point where water erodes the material and threatens a turbine’s performance.

• •

• •

Outline the coverage area of the blade with masking tape.

While one repair technician dispenses the protective coating onto the leading-edge surface, a second tech should distribute the coating with a brush at a low angle, using smooth, consistent brush strokes. These strokes should occur in a parallel motion to the leading edge of the blade.

After application, use a wet thickness gauge, which confirms the proper coating thickness.

Once satisfied with the

Several options on the market include innovative cartridge and applicator systems to ensure accurate mixing and reduce the possibility of error and waste.

Why use it: Fillers offer an extra layer of defense against blade damage caused by sand, rain, erosion, or other minor impacts. If a blade has sustained minor damage, epoxy or polyurethane fillers can be applied to quickly repair surface damage.

Best practice: Fillers can offer a quick fix to minor blade damage, but typically more careful application

The close-up of a blade’s leading edge shows initial erosion. Such damage compromises the integrity of the blade and lowers its aerodynamic efficiency, causing a loss in annual energy production.

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Polyurethane coatings provide another option for blade protection, offering a layer of defense against damage caused by sand, rain erosion, and minor impacts. But proper application by brush or casting is necessary for full protection, so coatings are best applied in controlled conditions and not in the field.

is required by brush or casting for full protection. In these cases, coatings are best applied in controlled conditions.

Additionally, because blades flex significantly during operations, fillers must allow for some bend while providing enough durability to prevent surface cracking. These products are typically applied to the base of the leading edge of a blade, so it is imperative to pair fillers with an additional coating or protection tape to effectively protect them from erosion or leading-edge damage.

A variety of fillers are available so before deciding on a product users should factor in the application method required, the repair time available, and the performance expectations in the field. Also, review the instructions to ensure proper mixing and adhesion to the substrate of a blade to decrease the possibility of application errors and waste.

• •

Apply a light coat of filler to the repair area, using firm pressure to ensure appropriate contact and bonding.

Slowly build thick, wet coats of the filler until the repair area is slightly

• •

higher than the surrounding blade.

Let the filler cure for the product’s instructed time.

Once cured, sand the filler close to the surrounding blade area, then prime and paint as per the manufacturer’s recommendations.

In the wind industry, it is essential for OEM’s to identify the products and practices to reduce leading-edge erosion on blades and maximize turbine performance. By implementing a combined strategy of prevention and repair, operators can extend the service life of their turbines. Most importantly, proactive erosion strategies can lead to a substantial increase in AEP and a better return on investment. W

One of the most commonly used products for leadingedge erosion is bladeprotection tape. Look for a durable product that is UV stable.

BONDING APPLICATION TOOLS In addition to blade repair tapes and fillers, there are preventative tools that can extend the lifetime of wind turbines. These tools can enhance the design, aerodynamic efficiency, and AEP of turbines.

For example, when bonding composite blades or securing aerodynamic attachments (such as vortex generators), manufacturers and wind technicians should routinely apply a quality bonding solution. Depending on the project, these products offer additional blade strength, durability, and environmental resistance.

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•

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Acrylic foam tapes These tapes are typically used for applications that require reliable bonding or sealing because they provide rigorous flexing and fatigue resistance, making them ideal for turbine blades. As an alternative to liquid adhesives and mechanical fasteners, acrylic foam tapes are an excellent option because of their ease of application and ability to withstand residual forces — even in severe weather.

Best practices for applications are similar to the processes used for blade protection tapes.

Blade bonding adhesives These adhesives are used for bonding composite wind

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blades and provide a crack-resistant structural epoxy. By combining shear and peel strength with impact-resistance and durability, bonding adhesives offer a timely cure speed that can reduce turbine downtime during blade repairs. To ensure an adhesive is applied correctly, clean the surface of the blade and thoroughly mix the two adhesive components together. Next, apply the adhesive mix to the bonded area, and use contact pressure or clamps to secure the joined parts from moving around.

•

Structural adhesives Structural adhesives are room-temperature curing adhesives used for bonding composite wind blades.

As with bonding adhesives, it is important to clean the surface of a blade before application. Once the solution has been applied to the bonded area, use pressure or clamps to secure the joined parts until the adhesive has fully dried.

•

Dry layup adhesive Dry layup is a sprayable, synthetic elastomer-based adhesive used to hold glass fabrics and other reinforcements and materials (i.e. flow media) in place during infusion. During application, make sure the joined parts are secured while the adhesive dries completely.

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RE PA IR S

Lou Dorworth Direct Services Manager A b a r i s Tr a i n i n g R e s o u r c e s , I n c . w w w. a b a r i s . c o m

Turbine blade repairs should be kept as simple and effective as possible while retaining a blade’s structural and operational integrity.

Rik Heslehurst Senior Engineer A b a r i s Tr a i n i n g R e s o u r c e s , I n c . w w w. a b a r i s . c o m

Simplifying blade repairs with zoning and structural methods

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epair of wind-turbine blades is often a physically daunting and challenging task. Technicians are expected to suspend from ropes or use a gantry and often move about in awkward or uncomfortable positions to work on a blade. The physical challenge is sometimes more difficult than the repair work itself, and so a well-designed plan is essential for more effective time and cost-saving outcomes.

Other than leading-edge erosion, typical operational damage on turbine blades comes from lightning strikes, surface impacts, disbonds, or aging. Damage can result from a number of causes, including bird strikes, bullet holes, high-wind object impacts, moisture ingress, or the propagation of manufacturing anomalies. Regardless of cause, using a proven approach can ease the work for technicians and enhance its effectiveness on the blade. The goals are safety of the wind tech and retention of a blade’s structural integrity and operation. After all, there is little point in repair work if it doesn’t extend blade life.

To this end, a zoning method can offer a simple approach with substantial benefits. Zoning essentially divides a blade into sections or steps for repair. All repair schemes involve surface damage, so zoning the surface profile of a blade is highly recommended. Zoning of the blade surface profile is based on a combination of weight, strength, aerodynamic, and aeroelastic considerations.

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Airflow & aerodynamics A basic understanding of how airflow tends to move over the surfaces of a turbine blade can help determine potential erosion damage.

The flow of air over a blade is initially laminar or streamlined, and then tends to transition into a turbulent flow boundary layer at the blade’s maximum thickness. The thickness of the turbulence boundary layer steadily increases toward the blade’s trailing edge.

Typically, the surface profile of a blade behind its region of maximum thickness quickly becomes less significant to its aerodynamic efficiency. Therefore, flush repair surfaces are more important over a blade’s leading-edge region, back to about 25 to 30% of a blade chord length. Behind the 30% chord line, nonflush repairs will not adversely impact a blade’s aerodynamic efficiency.

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Types of damage seen in composite laminate blades

The resultant lift force at the aerodynamic center of the blade is about 25% chord length from the blade leading edge, and the shear center is about 34.5% of the chord length from the leading edge (for a uniformly distributed material blade cross section of typical airfoil shape). So, it is important for these repairs not to add significant weight behind the shear center.

Once assessed, the damaged area of a blade is categorized into one of three types: Intralaminar matrix cracks, interlaminar matrix cracks (delaminations), or fiber fractures (holes). Damage type will determine the ideal repair scheme.

Aeroelasticity is the interaction of the aerodynamic forces on a turbine blade and the blade stiffness in the chordwise direction. A key parameter in the blade stiffness for the aeroelastic phenomena of torsional divergence (the more common problem in high-aspect ratio airfoils) is the location of the chordwise shear center.

For effective repair, damaged turbine blades are typically zoned into four different regions. The zones are based on the aerodynamic and aeroelastic requirements, and focus on the repair requirements.

Aerodynamic structural repair

Repair method An effective approach to repairing composite structures follows a procedural method where each step helps determine the next most effective one.

1. Damage identification. First, the damage must be identified (usually visually). Then a non-destructive inspection or NDI survey (which requires in-situ positioning of the NDI equipment), should take place to determine the type and extent of damage. NDI techniques are varied and used to evaluate the integrity of turbine blades without destructive measures, such as cutting the blade cross section.

2. Damage zone and categorization.

Once the damaged area of a blade is located, the type of damage can be categorized as either: •

•

Aerodynamic structural repairs are a scarf type of repair, in which the damaged area is “scarfed out” to produce a uniform pattern of underlying plies.

Aerolastic semi-structural repair

An aerolastic semi-structural repair is much the same as an aerodynamic structural repair.

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•

Intralaminar matrix cracks extend in all directions through the laminate (microcracking).

Interlaminar matrix cracks are usually found in-plane between layers (delaminations).

Fiber fractures or broken fibers occur from a medium to highvelocity impact.

3 Evaluation. Engineering evaluation of the type of repair required is based on the blade zone. The damage type determines the repair scheme.

4. Damage area preparation. A damaged blade must undergo preparation for the repair installation at the local damage area. The damaged

section is typically removed based on the selected repair scheme. This is an in-situ activity, and the purpose is to remove as little blade material as possible for preservation of undamaged (good) laminate material, effectiveness of the repair, and the speed in which the repair can be accomplished.

5. Repair scheme fabrication. The repair scheme is often determined at ground or platform level, and based on a map of the damaged ply removal geometry and fiber axial orientation.

The scheme is either pre-cured or prepared as a prepreg or wet layup type of patch, and readied for installation. When possible, vacuum bagging materials are pre-assembled to install prior to applying the repair patch.

6 Installation. The repair scheme is installed over the damaged region.

Speed of the repair application is essential when working with an uncured resin system.

7. Cure. The repair must be given time to cure, which will depend on the recommended cure time of the resin.

Application of heat can accelerate the cure time but must be controlled at an appropriate temperature.

8. Inspection. The repaired area is visually inspected and approved by an applicable NDI technique.

Repair zoning To assist in the effective and efficient repair of damaged blades, a turbine blade can be zoned into four basic regions. These repair zones are based on the aerodynamic and aeroelastic requirements, but focus on the repair requirements.

Zone 1. The first zone refers to a blade’s leading edge for aerodynamic and structural purposes. It requires maintaining a blade’s mold line (D-nose shape) to be maintained for the laminar boundary layer. Zone 1 is from the 20 to 100% span length, and

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to 25 to 30% of the local chordline. It will always require a flush repair.

repair ply. It acts as an environmental seal for the repair assembly.

Zone 2. Though not a major structural region of the blade, the repair scheme for Zone 2 must be weight conscious. It should not add significant weight to the blade for blade-mass balance. This area requires an aeroelastic semi-structural repair.

2. Aeroelastic semi-structural repairs Where a semi-structural repair is required (i.e. the repair will provide retention of damage tolerance but not necessarily full strength restoration) and minimal weight is necessary, then a scarf repair patch with a less shallow scarf angle is recommended. So if a 5 to 10° scarf angle is prescribed, the overlap length and adhesive shear load-carrying capacity can be determined from these equations: The overlap length of repair on a damaged blade is determined by two things: depth of the damaged material that’s removed and the scarf angle for the repair, as shown in this equation.

Zone 3. Repairs in this part of the blade are designed primarily for aeroelastic purposes. The repair need not be flush for airflow aerodynamics. However it should not add significant weight behind the shear center position either. (Note: trailing-edge repairs in this zone are typically flush to meet both aeroelastic and aerodynamic requirements.)

Zone 4. These repairs need not be aerodynamically smooth. Depending on the severity and location of the damage to the main load-bearing region, the repair may need to be semi-structural or structural by design. Because of the large enclosed area of a blade in Zone 4, its torsional rigidity is much higher than in Zone 3, hence aeroelastic requirements are not necessarily critical. But significant damage to Zone 4 training edge may need a flush semi-structural repair.

Recommended repair schemes 1. Aerodynamic structural repairs Aerodynamic structural repairs are taperscarfed around a damaged area that has been removed to produce a uniform pattern of underlying plies. The scarf angle necessary for a structural scarf repair is typically 3° or less, or at a prescribed ratio that may differ lengthwise vs chordwise.

A layer of resin or adhesive is first placed onto the scarfed region. The repair plies are laid down in a matching ply orientation pattern typically with a filler ply installed first over the repaired core materials. This will aid in like-orientated repairs – laying a ply over the likeorientated parent structure (for the most effective load transfer). Sometimes, an outer-most adhesive layer or thin glass ply is applied over the patch, about 5 or 6 mm larger than the outer-most structural AUGUST 2016

Repairs_8-16_Vs4.indd 45

l overlap = 2 l seal edge+

h damage depth tanqscarf

+ l 1st ply

The shear load-carrying capacity of the scarf adhesive for the repair can be estimated using this equation.

P adhesive shear = Ee allt =

2tphdamage depth sin

2q scarf

where: tp= the adhesive maximum shear strength

Equation terms • E: Young’s modulus of the patch or parent laminate • Epsilon-all: The allowable design strain in the laminate (typically up to 0.002667) • t: Thickness of the parent laminate A benefit of the aeroelastic semistructural repair is that much less material is removed from the original (good) structure to complete the repair.

3. Semi-structural repair This type of repair does not require a fullstrength restoration or aerodynamic or aeroelastic consideration. Restoration of damage tolerance would require a semistructural repair. A significant proportion of the internal damage is filled with a lowmodulus plug (the plug is not designed to carry much load). The scarfed section and doubler will transfer load around the plug area. The principle of the design is for relatively thick structures, but it limits the removed damage area and the resulting repair size.

After bonded insertion of the plug, the scarf repair follows the same process as described for the aerodynamic structural repair. The doubler patch is laid up with the smaller ply down first. This

A BRIEF GLOSSARY OF COMMON REPAIR TERMS Aeroelastic: The behavioral interactions between inertial, elastic, and aerodynamic forces when subjected to fluid (air) flow.

Chord: The aerodynamic breadth or width of a wing or airfoil.

High-aspect airfoil: A long, narrow (chord) airfoil — it is typically defined as a ratio of the wingspan to chord.

In-situ: Latin for in position or in place; it also means locally.

Prepreg: Fiber or fabric that has been pre-impregnated (or wet-out) with resin. windpowerengineering.com

Scarf angle: Taper angle of a scarf joint. (In blade repairs, a plain scarf refers to two flat planes meeting on angle relative to the axis of the stock being joined.)

Scarf: The scarf joint, or creating the taper angles for the scarf joint.

Syntactic: A resin filled with lightweight fillers that give it foamlike qualities, which let it stay in place in thick sections and without sagging or running. (The term is often referred to as “syntactic foam,” See reference: https://en.wikipedia.org/ wiki/Syntactic_foam) WINDPOWER ENGINEERING & DEVELOPMENT

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REPAIRS

Semi-structural repair

Non-aerodynamic structural repair

Typically a blade that does not need a full-strength restoration requires a semi-structural repair.

first doubler ply and each subsequent ply will overlap the corresponding exposed plies in the structure. The doubler patch should be of the same configuration as the plies where the plug is inserted and have the same thickness of the plug.

Non-aerodynamic structural repairs This type of repair is recommended for substantially thick structures where aerodynamic requirements are unnecessary, but geometric efficiency is important (such as for smaller repair sizes). Designing a repair that includes bolts can get involved. Many turbine manufacturers have not yet used or researched bolted repairs, but they can be done in the root section of a blade (or in thick, solid laminate areas) with little removal of good material. This typically applies where

Non-aerodynamic semistructural repair

This type of repair is ideal for shallow depths that do not require the substantial removal of material.

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These repairs work best on substantially thick blade structures where aerodynamic requirements are not necessary, but geometric efficiency is still important.

manufacturing defects are present, such as in large, infused blades. This type of repair can also apply to damaged spars (or webs).

Pay specific attention to lowering bearing stresses in composite components.

This is accomplished by appropriate bolt material and size selection, with a bolt pitch of 4 to 6 diameters. The plug used to fill the damaged region, if not considered a structural component, should be a low modulus material so as not to attract load.

A metal plate or pre-cured composite doubler is typically used as the patch material. Give special care and attention and when sealing, and watch for corrosion issues (with metals). When aerodynamic profiling is needed, chamfer the plate or use countersunk bolts and double their number in the process.

Aerolastic semistructural repair

This repair type is for minor blade damage, such as surface abrasions or surface matrix cracks.

Non-aerodynamic semi-structural repairs This involves a low-modulus plug and inverted structural doubler for repairs that require restoration of damage tolerance that is not aerodynamically sensitive. The repair is ideal for shallow depth repairs that do not require substantial material removed for a scarf repair.

Non-structural repairs Minor or negligible damage will still need a form of repair. Minor damage is typically surface abrasions and surface matrix cracks that are repaired with a non-structural or cosmetic repair.

The repair procedure is to fill the surface damage with either a resin or a lightweight syntactic paste to the surface profile, followed by application of a thin glass fabric layer over the filled damage surface to keep out the elements. There is no need to remove the damage because cutting fiber may then require a semi-structural or structural repair.

Repairs to erosion pitting are approached in a similar manner, but may require only a “fill and fair” repair with syntactic paste. This can be finished later to the aerodynamic surface prior to paint or a urethane boot application.

The repair schemes mentioned are tailored to solid laminate construction, but adapt to sandwich structure construction. Sandwich panels are those that contain core materials.

Repairing wind-turbine blades in the field is a challenging undertaking, one that deserves a well-defined plan and repair method. Repairs to large-scale damage (spanning multiple zones) or lightning strike damage may require additional repair design considerations. W

www.windpowerengineering.com

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windpo

A WIND FARM’S

THE BALANCE OF PLANT (BOP) is the most important link for delivering power produced by a wind farm to the marketplace. The BOP consists of the pad-mount transformer at the base of the wind turbine through to the collection system and substation. The BOP also includes transmission lines, met masts, and the roads and drainage.

BALANCE OF PLANT ALSO NEEDS AN INSPECTION

JUDAH MOSESON PE CEM, VP – OPERATIONS COOKE POWER SERVICES

The IR image shows three loose or damaged connections (SP 2, 3, and 6) at a padmount transformer. Three on one side of the photo are the three phase cabling from the wind turbine generator and the other side are the three phases cabling increased to 34.5 kV that goes to the substation. Loose or damaged connections are responsible for the increase in heat, the good connections remain cooler.

While most O&M discussion focuses on components in the nacelles, the BOP equipment also needs attention. It is wise to plan for best-in-class BOP inspection and maintenance procedures to maintain a highly functioning wind farm. The inspections outlined here represent essential activities that help ensure safe and profitable operation of a wind farm.

The challenge for wind-farm owners and operators is to recognize the need to budget for these procedures.

Their costs represent less than 10% of the total O&M budget of a typical wind farm. To keep that link in power production up and running, this article focuses on how to inspect the medium-voltage (MV) equipment from the pad mount transformers, collection system, substation, and the high-voltage (HV) equipment in the substation.

Pad-mounted transformers These transformers are required to take the 600 to 900V generator output and step it up to the MV of the collection system (typically 34.5 kV) for efficient transmission to the substation.

The transformers have had a number of issues over the last 20 years that have required an action plan for inspection and maintenance.

IR inspection is a non-evasive examination of the transformers online and under load.

The accompanying image shows loose or damaged connections.

The results of the inspection are known immediately and a brief outage is typically all that is needed to correct the issue. Without an inspection, loose or damaged connections may eventually fail, causing damage to the transformer and posing a safety risk to personnel.

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A WIND FARM’S BALANCE OF PLANT ALSO NEEDS AN INSPECTION

Oil sampling of the transformers is a typical practice. Unfortunately, the wind industry has been slow to react to the results of this testing.

A preferred action plan should be to identify the root cause of the poor test results and take corrective actions such as internal repairs followed by oil replacement. The most common test results show an increase in dissolved gasses (DG). These typically include hydrogen, methane, acetylene, ethylene, and ethane. High DG concentrations can explode when a unit is switched in and out of service.

Most sites simply hang a red lock on these units and identify them as “do not operate.” An individual wind turbine can no longer be isolated at the troubled transformer, so a turbine string outage is the only way a crew can perform maintenance on the associated turbine.

Recently, an oil-filtering method has come into the marketplace that may extend the life of transformers with high DG. This filtering process draws a vacuum on the oil reservoir and presses the oil through specialized equipment that removes the gasses and water from the oil.

Results can be documented with a post-filtering oil sample analysis. This process, however, does not repair the transformer.

The breakdown of electrical insulating materials and related components inside the transformer generates the gases. Typically, the replacement cost of a pad mount transformer ranges from $25,000 to $60,000 depending on input and output voltages.

The collection system has several supporting components but the single most important one is the connecting MV cables. MV cabling runs between the pad-mount transformer at the base of the wind turbine and substation, and is either above ground or below.

Above-ground MV circuits require more inspection and maintenance than below-ground options.

The same IR inspection performed on the padmount transformers can identify loose or damaged connections. Additionally, the visual inspection of poles and mounting equipment is required to ensure the collection system is in good working order. Birds and reptiles tend to nest on and climb on these structures. Fortunately, a range of hardware attachments is available to discourage wildlife from homesteading on this equipment.

Below-ground MV circuits are costlier to install but require less maintenance. The exception is an occasional ground fault or splice failure. A ground fault may occur when a cable is damaged by a sharp or heavy rock. A “Thumper” is used to pinpoint the location of ground faults, with information from the fault recording relays in the substation.

Damage is repaired with a new cable splice. Many cable splices from original construction remain below ground and are a common failure point in the cable. As a result, the original splices can fail. The repair method is the same as for ground faults. It is customary to make cable splice repairs above ground and cover them with a protective splice box.

The transformer will still produce DG, but it may provide for an extended period of safe operation until the gas level becomes too high again. Periodic oil sampling will let an owner or operator know if this process results in months or even years of normal operation.

This cable splice was made above ground and now resides in a protective splice box.

Transformer vaults are the pedestal pad-mount transformers rest on. An initial practice in the wind-farm construction industry was to set transformers on vaults made of fiberglass. In some instances, fiberglass vaults have proven inadequate.

Inspections showed the transformers leaning, sinking, or moving past the limits of the cables buried beneath them. A typical response is to replace the fiberglass vaults with precast concrete vaults. This repair is sufficient to solve the problem for the life of the plant.

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This IR image shows a loose or damaged connection in a substation.

Substations contain the most typical equipment found at a wind farm.

Transformers, breakers, switches, relays, and more are subject to regulatory protocols. These protocols determine the schedule and scope for inspections, and are in place to ensure safety to personnel and equipment. Most wind-farm owners or operators perform these tasks during the low-wind season to reduce their loss of generation and revenue.

The most useful tool again is the IR inspection camera because it can quickly identify loose or damaged connections within the substation.

It is also important to ensure that potential safety risks, such as sufficient substation yard stone and weed control, are an essential part of the maintenance program. The yard stone serves several purposes but most importantly it provides a high resistance layer – insulation – between our foot and the ground. The weeds, if not kept under control, can quickly grow tall and may provide a path for a dangerous ground fault within the substation.

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A lot can go wrong on a wind farm and not all risks are found up-tower or in the nacelle. BOP equipment, including padmount transformers, splices, and others are as essential for getting wind-generated power to the grid as the generator. Damage to a single splice or cable and a string of turbines can go offline. BOP equipment should also receive routine inspections to optimize wind-farm operations.

The good news is that there are highly qualified third-party service providers available to perform all the necessary inspections and maintenance throughout a wind farm’s BOP. W

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WIND TURBINE UPGRADES GET

LEGACY TURBINES READY FOR

MORE PRODUCTIVITY AND

LONGER LIFE

MOHAMAD MURYWED SALES AND BUSINESS DEVELOPMENT MANAGER ABB’S WIND RETROFIT GLOBAL SERVICES

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A

s the wind energy market matures, assets are ageing with many turbines now passing the end of their design life. Operators are moving towards more powerful and sophisticated equipment rated at two megawatts (MW) and more.

The result is that fewer OEMs offer turbines below 2 MW and as the market matures, larger manufacturers have acquired their smaller competitors and then streamlined their portfolios. As a result, some OEMs are limiting their support to those older turbine models.

While new wind turbines have their place in the wind power mix, there is a growing demand for upgrading assets of a certain age.

Then and now Early turbines were two-speed designs, with low and high-speed generators for different wind conditions.

Today’s turbines are fitted with wind converters which include power electronics and variable-speed mechanisms that ramp up production as the wind speed increases. This let operators maximize production regardless of wind speed. Recent wind converters can adjust the rotation speed of the wind turbine to suit the wind conditions. This reduces stress and loading forces on the drivetrain while maximizing energy transfer.

There are more than 30,000 legacy turbines in the world (5,000 in the U.S.) that do not have power electronics, and their warranty periods have ended, leaving operators with limited access to spare parts, turbine data, and support. Owners, therefore, face a range of possibilities. They can choose to extend their warranties, refurbish their turbines, or repower the sites with new turbines. Operators that self-maintain their fleet usually opt-out of warranty extension The incentives differ between markets. In the U.S., turbine height limitations and transmission system bottlenecks leave owners with the option of retrofitting wind turbines instead of repowering the sites. The government is compensating for this with renewed production tax credits (PTC) which allow a refurbished turbine with investment of 80% of turbine market value, to be treated as brand new one in terms of subsidies.

In other markets such as Spain, it’s business as usual and owners get continuous tariffs if they extend the lifetime of turbines beyond the originally planned

Refurbished turbines have begun their second life at a wind farm in Denmark.

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WIND TURBINE UPGRADES GET LEGACY TURBINES READY FOR MORE PRODUCTIVITY AND LONGER LIFE

TOP: Turbine hubs and spinners await assignments to refurbished turbines at ABB’s Barcelona factory.

BOTTOM: Turbine nacelle has been refitted with a new generator for the turbine’s next assignment.

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20 years. In countries with limited land and good wind resources, such as Germany, Denmark, and Netherlands, government incentives promote dismantling old turbines and repowering the sites.

Repowering involves replacing existing wind turbines with new ones which are often more powerful. However, their acquisition demands greater financial commitment and implies a series of lengthy administrative procedures in addition to the time it takes for the acquisition and installation of the wind turbine. If they opt for replacement and repowering, they can partially offset the cost by selling their aging turbines in the used-turbine market.

Buyers of used turbines include small community-based operators in remote locations and on islands. Although the turbines are second hand, they are mechanically and electrically refurbished for greater performance. Second hand units are also engineered to meet the demands of new grid codes and power limitations based on applicable government subsidies. Power generation in those communities is typically on a smaller scale with one turbine or three at the most. Operators are often farmers looking to boost their income, or industrial and mining customers who will use the turbines connected or off-grid to reduce fuel consumption from diesel generators, and clean up their energy supply. Buyers can acquire refurbished second-hand turbines at around half the price of a brand-new equivalent and with a lead-time of only a few months.

Refurbishing turbines offers affordable solutions, and provides means for clean, accessible electricity, and better living standards. Recognizing this, ABB identified the opportunity of re-engineering aging wind turbines with ratings below 2 MW to bring them up to modern standards.

The reconditioning offered by ABB consists of integrating a full-scale converter equipped with cuttingedge power electronics as well as retrofitting certain mechanical and electrical components. The reconditioning aims to increase productivity and extend the useful life of the wind turbine.

The integration of the converter means that the wind turbine can work at a variable speed to adapt to the wind conditions similar to how new wind turbines operate. This lets them work at an optimum operational level, achieving the maximum transfer of energy between the wind and blades and while easing the stress on the power train. Moreover, the reconditioning cost is clearly lower than that of a new equivalent wind turbine with a reduced installation time depending on the needs of the owner and the conditions existing prior to the update. www.windpowerengineering.com

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The generator is on a test bench at the ABB Wind Retrofit Center of Excellence. A rebuilt generator is tested prior a new work assignment.

Renewing the components and technology of an existing wind turbine represents a great option to continue achieving a return on the initial investment of the wind farm where there are limitations on time and economic resources. This on-site service is available to operators to help them extend lifetime of existing turbines and improve a wind farm’s Return on Asset by correcting operational issues. This leads to more production, lower mechanical stress and O&M costs, and increased availability with access to spare parts.

This also gives access to state-ofthe-art data analytics with machine learning and remote condition monitoring capability. This enables data driven predictive maintenance and asset health monitoring to optimize wind turbine performance, minimize levelized cost of energy, and extend operational life of assets.

Upgrades with full power conversion Full power converters are installed at the bottom of the tower, either in a switchgear room or in a separate electric room. The equipment lets operators meet the requirements of the latest and most demanding grid codes. The new technology provides reactive power production and low voltage ride through to improve power quality by smoothing fluctuations of motive torque, and to minimize curtailment.

Previous generations either did not use a converter or used doubly fed converter technology in which only one-third of the power passed through a converter. This can lead to problems with grid connectivity and reliability. Passing all generated power through a full power converter overcomes the shortcomings of previous electronics and ensures the output meets the latest grid codes.

Transforming an old two-speed turbine (with fixed or variable pitch) to a AUGUST 2016

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variable ramping-up mechanism requires electrical modifications to the generator.

This entails removal of slip ring or rotorcurrent-control mechanisms, re-winding to remove the lower speed, and increasing the electrical and heat insulation. The new design is an induction type fully fed from the stator side for either refurbished or new generator.

The modified generator has similar dimensions and does not add extra weight to the nacelle. This avoids the need for structural modifications, which would be necessary to ensure that turbines can withstand the physical loads imposed by the wind on the blades, nacelle, and tower.

With a full power converter, an operator gains additional production by moving to a variable-speed mechanism, meaning they will make the most of the wind across full range of speeds. This solution does not increase the nominal power beyond design limit and therefore does not require any re-certification.

To meet this growing demand for modernization and customization of wind turbines while providing reliable and efficient global solution, ABB created the Center of Excellence for Wind Retrofit in Barcelona, Spain. This engineering center makes it possible to give a new and better life to old wind turbines. W windpowerengineering.com

A peek inside the cabinet of a full power controller.

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smart

drones & SMALLER SENSORS READY FOR MORE WIND FARM WORK

Grant Leaverton Vice President & General Manager Advanced Aerial Inspection Resources (AAIR) www.aairteam.com

T

he commercial drone industry is evolving at a rapid pace. Each change or advancement means application of Unmanned Aircraft Systems (UAS) can enter another market and provide a service that typically cuts costs and enhances safety. To date, UAS’ have provided service in industries such as military, security, search and rescue, construction, agriculture, real estate and land surveying, insurance, and others.

The wind-power industry is no different, and many windfarm owners capitalized on drone use early with unmanned inspections of their turbines. In some instances this eliminated the need for traditional climbing, and rope-based or platform inspections by wind technicians. UAS have led to significant operations and maintenance savings and, most importantly, reduced safety risks at many wind sites.

While adoption of UAS is increasing so are the machines, which is leading to new ways and reasons for using them. It is also leading to new techniques and skillsets required for proper and safe drone operation. For example, in the wind industry, turbine and blade inspections are no longer the only useful purpose for UAS. Wind-farm owners are starting to employ them for aerial inspection of power lines and transmission interconnects.

As the reasons for using drones evolve, it is imperative to keep track of the regulatory framework governing their use and maintain skills to operate the new and upgraded machines.

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Commercial-grade drones are proving to be more than a novelty. Advanced optics, cameras, battery life, data analytic systems, and the ability to remain stable in strong winds means these machines can provide a valuable service at wind farms. Drone inspections of turbine towers and blades can save a wind-farm owner time, costs, and safety risks over rope-based inspections.

Now drones are proving even more useful at wind site, and the safer option for aerial inspection of power lines and transmission infrastructure.

An AAIR drone or unmanned aerial system (UAS) begins turbine blade inspections at a Texas wind farm. According to Navigant Research, cumulative global revenue for turbine UAS sales and inspection services is expected to reach nearly $6 billion by 2024.

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Smart drones & SMALLER SENSORS READY FOR MORE WIND FARM WORK

Turbine blades to transmission lines New drones are entering the marketplace every week. Advancements in autonomous flight, sense-and-avoid features, and feature recognition technologies are now available in many off-the-shelf units. Drone sensors are getting smaller and smarter. At the same time, the data sets that drones are capable of collecting remotely are getting bigger. This benefits some users who can attain greater use and data, employing drones for more than one task.

The wind industry is a prime example where drones have increased their reach and value. Wind-farm owners are now able to employ drones for tower, blade, and transmission inspections. This is no small accomplishment: where regular blade inspections might prevent an unexpected failure that could bring down a single asset, failure of a wind site’s transmission line could potentially bring the entire park offline.

Today’s commercial drones are ideal for performing comprehensive aerial inspections (CAIs) of transmission assets. A CAI is a highly detailed inspection meant to spot the smallest of defects, such as loose or missing cotter pins on a conductor attachment. UAS-driven CAIs can even detect hairline cracks in critical welds.

This type of inspection reaches far beyond basic aerial patrol and yields a much higher probability of defect detection. The detail and data obtained lets site owners determine the overall health of their system and make early O&M and repair decisions to prevent unplanned outages.

In addition to the higher quality of data provided

by UAS, drone inspections eliminate the need for helicopters and climbing patrols and provide a safer and more cost-effective option.

Routine transmission-line inspections are just one application where drones are proving useful at wind sites. Storm damage assessment is another.

Mother nature can wreak havoc on transmission lines. This is especially true at wind farms because

they are purposely situated in high-wind regions. Whether it is 200-plus mile-per-hour winds or an ice or lightning storm that hits a wind site, preventing failure is not always an option. A poststorm assessment is routine O&M protocol at wind farms, and drones can also make this process simpler, safer, and less costly.

For example, downed lines present unique hazards for repair crews, and the ability of UAS to bypass these hazards and provide a real-time view of a work area is of high value for linemen. It lets a repair team identify hazards before workers enter an area and helps them decide on the right tools and equipment for the job. This insight keeps workers safer and expedites the restoration process.

A commercial-grade UAS, handled by an experienced operator, can provide safer and typically higher-resolution visual assessments than ground or rope-based inspections. For this reason, drones are increasingly becoming the method of choice for turbine blade inspections at wind farms and even for comprehensive aerial inspections (CAIs) of transmission assets.

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Rule changes As regulations change, the use of UAS for transmission line inspections will likely become more common. As it currently stands, drones must fly only within visual line of site (VLOS) of the operator. This limits the range of flight to 1,000 to 2,000 feet, depending on how large the UAS. It is expected Federal Aviation Administration (FAA) regulations will change and eventually allow beyond visual line of site (BVLOS) operations of UAS. When this happens, users can add longrange aerial patrol to the list of viable uses for transmission line inspection by drones. This provides for a much higher-level inspection of the asset, and is a critical function of managing a rightof-way from possible encroachment and vegetation management.

The FAA’s recent Part 107 “small rules” release moves the industry a step closer to long-distance flights. Part 107, which takes effect August 29, 2016, permits commercial flight of drones weighing less than 55 pounds, at a maximum speed of 100 mph, below 400 ft. AGL (above-ground level) during daytime (and as long as they remain within the line of sight of the operator).

Although the new rule does not permit BVLOS operations, it opens discussions by stating that consideration of certain waivers of operational restrictions would take place if the operator could prove an equivalent level of safety.

This means that the line of site restriction may be waived in certain situations. Experts in the utility industry are predicting that certain BVLOS waivers for overhead line inspection will be granted within the next 12 months.

Part 107 has another significant ruling as well. The regulation eliminates the once-required FAA pilot’s license to fly a commercial drone. A UAS pilot certificate is still required but much easier to obtain and can even be done online. This change is significant because it lowers the qualification standards for drone operation and opens the door to new talent.

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that the original regulations were extremely prohibitive to would-be drone operators.

Benefits of the new rules include reduced costs to get licensed for drone operation and increased operational flexibility for owners. There are other minor changes in the regulations that are available on FAA’s website.

The advancements in drone capabilities and new regulations for commercial drone use mean it is imperative for users to keep up with the ever-changing UAS industry. These changes also open the door for new industries to take advantage of the many potential benefits drones can offer, and for older industries to research new uses for UAS. As the capabilities of drones advance and the opportunities increase, one thing remains clear, drones are here to stay. W

windpowerengineering.com

A CAI is a highly detailed transmission line inspection meant to catch the smallest defects, such as loose or missing cotter pins on a conductor attachment or hairline cracks in critical welds.

Current rules state that drones must fly only within visual line of site of the operator, which limits flight range to about 1,000 to 2,000 feet.

It is expected FAA regulations will eventually change so users can add long-range aerial patrols for transmission line inspections to the list of viable uses by drones.

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A D

IND E X

AeroTorque........................................................................ 25 Amsoil, Inc........................................................................ BC Aztec Bolting........................................... cover/corner, 31 Bachmann Electronic....................................................IBC Campbell Scientific.......................................................... 13 CANWEA............................................................................59 Castrol................................................................................ 15 Dexmet Corp....................................................................... 9 Gradient Lens....................................................................28 Mattracks.............................................................................. 3 Moog Components Group.......................................... IFC Norbar Torque Tools, Inc................................................ 19 Renewable NRG............................................................... 27 Schaeffler Group.............................................................. 23 Zero-Max, Inc...................................................................... 5

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WINDPOWER ENGINEERING & DEVELOPMENT

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AUGUST 2016

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TOP: KPS’s kite system operates in two reciprocating phases. In phase one, the wing flies in a circular looping path akin to the tip of a turbine blade. In phase two, the pitch of the wing is actively changed and retracted to minimize the aerodynamic force, and the kite exits the loop. The kite is held in a static, overhead position and then glided back to a starting point, alternating positions with the second kite.

BOTTOM: KPS says its two-kite system can optimize power generation by flying at heights where winds are stronger. The system comes with a grid-compliant generator so there is no need for external power conditioning.

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U.K. inventors want to tap into 100-mph winds way up A FEW HUNDRED METERS UP, out of the reach of conventional technology, the wind blows at a tantalizing 100 mph. How can something tap that energy stream?

Kites and tethered flying systems have been tested and proved only partially successful. But those plucky Brits want to try again, forgoing steel and composites for tethers and lightweight structural textiles.

The design from Kite Power Solutions’ (KPS) flies on a 500 to 700-m long fiber tether that attaches to a winch system.

When a kite reaches flight speeds, up to 180 mph (80 m/s), tension on the tether rapidly unspools line from a drum. This turns a generator, which then produces electricity.

Kite-generated power, of course, is nothing new. Several European developers are currently on the market. Closer to home in the U.S., Google acquired Makani Power in 2013, which developed a system that generates electricity with a tethered, multi-turbine kite structure (that resembles an airplane). In 2014, Altaeros Energies launched a tethered, high-altitude floating turbine in Alaska. The “BAT” (buoyant airborne turbine) is an inflatable, helium-filled ring with a turbine suspended inside that can float at a height of 300 m, where winds are typically stronger than at 80 m up.

What makes KPS’s system unique is that it employs two kites in the same air space. While one flies high and strong, reeling out and generating power, the other is kept low and slow — reeling in, until their tasks are swapped. The asymmetric operation means energy production is more constant and the alternator is kept rotating at a near-optimal speed.

Tension on a tether reeling in can be reduced by a factor of 10 or more. The reciprocating action produces a net energy gain. The result? System yield is expected to reach a capacity factor that is 10 to 15% higher than existing horizontal-axis wind turbines (HAWT) in a similar wind environment — this is according to an independent review by BVG Associates and Imperial College in London. Horizontal axis means the rotating axis of the wind turbine is horizontal, or parallel with the ground.

Max HAWT operating velocity is typically 25 m/s at hub height in winds about 60 mph. KPS’s system typically flies in 100 mph winds at a height of 450 m, which is twice the height of a large HAWT. Flying the kites at different altitudes also reduces their wake effect and increases yield. According to KPS, flying a wing in a circular path in the generation phase creates an efficient wing. Little energy is needed for

WINDPOWER ENGINEERING & DEVELOPMENT

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actuating a wing control mechanism.

KPS’s units are equipped with sensors to ensure their tethers do not tangle.

To date, this system has shown less impact on birds compared to conventional turbines. KPS is further studying potential affects on avian life.

Along with cheaper material and manufacturing costs (KPS’s twin-kite system even shares one foundation), a key benefit to kite power is its potential to reach higher altitudes where wind power is stronger and more consistent.

The system can also scale to much larger kites, flying at hundreds of meters, without much concern for storms so long as lightning is not in the forecast (if so, the kites can be retracted closer to the ground).

The company is currently targeting the offshore-wind market because it maintains its kite invention can reduce the capex of conventional offshore turbines by as much as 50%. After all, the patented power system doesn’t require large quantities of steel or specialized installation vessels. Offshore wind installations in the UK are achieving a levelized cost of energy about $184/ MWh, and are projected to fall to $102/ MWh by 2020. KPS expects to reduce that cost to about $66/MWh by 2020.

Earlier this year, the company secured a £1.0 million grant from the UK Government’s Innovate UK Energy Catalyst to accelerate the development of its kite-power generation system.

The grant will be used to scale-up the company’s system to a 500-kW kite turbine and validate the commercial viability of its 3-MW floating offshore arrays. The two-year project also includes a program to engage with the public and environmental interests to assess the impacts of the potential offshore kite rollouts. W

www.windpowerengineering.com

AUGUST 2016

8/23/16 1:34 PM

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