July 2013

Introduction
Wind turbine bearings and gearbox life issues have long plagued the wind industry.  Since 2007, NREL has focused on industry solutions with their Gearbox Reliability Collaborative (GRC). They have used the NEG Micon 750 KW NM48 wind turbine as their study model.  Recent meetings at the GRC have highlighted WEA damage as a common denominator in wind gearbox problems and impact loading as a potential root cause.  But where are these impact loads coming from?

In May, 2011,  AeroTorque (then known as PT Tech Windproducts) partnered with a wind farm in the United States to study transient load events in their NEG Micon NM48 750kW wind turbines using AeroTorque’s new torque monitoring system, the WindTM.™  Phase I focused on understanding the magnitude and frequency of transient torque reversals in the drive system.  These reversals are known to cause concentrated loading on skewed bearing rollers, which could potentially initiate White Etch Area (WEA) damage in bearing races.  These damaging reverse loads impact bearings and gears in the gearbox and are suspected of shortening the life of all drive system components, including blades and generators.  Generally, the greater the reverse loads and the more often they occur, the shorter the life of any highly stressed component.  If significant torque reversals were measured, Phase II would evaluate a new type of asymmetrical torque control device, the WindTC,™ capable of reducing both the magnitude and the frequency of the torsional reversals.  If the WindTC effectively damped the reverse vibrations, Phase III would be to begin retrofitting these turbines with the WindTC.

Results Summary
Phase I:  One of the wind turbines was shut down for three hours to install the WindTM, monitor.  Data was collected for several months, with the WindTM, recording numerous transient torque reversal events.  More importantly, each event resulted in several actual reversals, as the mass of the rotor and the mass of the generator wound up against each other and unwound back and forth in a classic torsional ringing action.  Enough evidence was collected to proceed to phase II. Figure 1

Phase II:  The first turbine with the WindTM, was retrofitted with a prototype WindTC Torque Control,  and a second nearby turbine was equipped with an additional WindTM,  to evaluate the two turbines operating during the same events.  Again, numerous transient torque reversal events were recorded on both turbines.  In every torque reversal event on the asymmetric torque limiter equipped turbine, the first negative torque was controlled to a maximum level of 40 percent of nominal turbine rating.  The turbine without the WindTC recorded torque reversals as high as 80 percent of nominal turbine rating and typically several additional torque reversals followed the first in each event.  Surprisingly, the slight amount of slippage in the WindTC during the first reversal so effectively damped the torsional vibration that no additional torque reversals were recorded.  The maximum torque reversal magnitude was cut in half, and the total number of torque reversals was reduced by more than 80 percent. 

The  WindTC also provided torque protection in the forward direction.  During Phase II, some up-shifting events on the unprotected turbine resulted in 200 percent forward torque overloads. The turbine with the WindTC during the same event had forward torque overloads effectively limited to 150 percent of rated turbine torque.  Image 1

After several months of flawless operation, the WindTC was replaced with a second prototype unit.  The first prototype was returned for a thorough disassembly and inspection.  It was found to be in excellent condition, with no measurable wear in either forward or reverse slip components. Wear life is projected to be 10–20 years with minimal maintenance.

As a result of the data collected in Phase I and Phase II, the wind farm has begun Phase III, the process of retrofitting their turbines with the WindTC. Future reports on this case study will include data on the effectiveness in reducing damage to bearings and gears, and reducing O&M costs of all drive components. 

A Detailed Look at Phase I
WindTM Torque Monitoring Installation:  AeroTorque partnered with  JR Dynamics, to develop the WindTM, a torque monitoring device, which allows for real-time torque measurement in a wind turbine drivetrain. Image 2

The WindTM monitor was magnetically mounted to the main shaft of the turbine, allowing for quick installation and removal.  The on-shaft unit communicated to a transceiver that allowed remote access to the data accumulated via cellular network.  Strain gauges on the main shaft measured both torsion and bending.  The cycling rate of the bending load in the shaft provided a measurement of the speed.  The monitoring unit continuously fed the data into a buffer. 

Looking for transient event data with continuous measurements can be like looking for a needle in a haystack.  The WindTM was designed to only record the worst 100 forward torque events and worst 100 reverse torque events over any monitoring period.  It does this by continuously feeding the data into a buffer.  When a significant torque transient occurs, the WindTM records the  eight seconds prior to the event and continues recording for 45 seconds.  It discards all the data in between the significant 200 events.  The events are also time-stamped to allow for syncing with SCADA and other data sources. 

Phase 1 Monitoring:  Numerous torque reversal events were recorded during Phase I, occurring almost daily.

This plot shows the results of a normal braking event on this turbine.  The aero-tips have deployed while the turbine is operating under partial power. 

Note:
• Black line is zero torque
• Red line is actual torque
• Dashed blue line is nominal torque.
• Dashed red lines are standard torque limiter settings

When the aero brake engages, the torque spikes in the negative direction, causing the system to wind up and unwind back and forth in the reverse and forward directions.  Each time the torque crosses the black zero line, the load zone on every bearing in the gearbox shifts approximately 180 degrees in the opposite direction.  In this instance, it occurs 11 times.

Many plots similar to the one you see here were recorded, in all types of wind conditions.  Surprisingly, even when the turbine power was minimal at the time of the aero braking event, similar transient reverse torque loads were experienced by the gearbox and drive system.

Phase II
WindTC Installation: After seven months of monitoring, the new WindTC was installed on the test turbine.  In addition, a nearby turbine was installed with a second WindTM torque monitoring device.  This allowed for direct comparison testing of turbine drivetrain loads during the same events.
 
The WindTC is the first torque limiter with asymmetric, independent settings for forward and reverse torques in a drivetrain.  Standard torque limiters used in some wind turbines have one setting, usually 150–180 percent of nominal turbine torque.  This limits only very large transient torque spikes in both directions.  Drivetrains are designed to handle these loads in the forward direction. JR Dynamics has instrumented the rollers in gearbox bearings on other wind turbines and found that during torque reversals the rollers in the bearings are skewed when these reversals occur. This causes concentrated loading of the rollers and damage to the rollers and races (to see this data, request a copy of the Gear Solutions article, “Troubleshooting Wind Gearbox Problems” February 2010).  The concentrated impact loading during torque reversals may be a root cause of White Etch Area (WEA) damage to the bearings that is known to dramatically shorten bearing and gearbox life in wind turbines.  The WindTC is designed to limit the reverse loads to 40 percent of forward torque setting (approximately 25 percent of nominal) and to dampen the overall torsional vibration. 

Reverse Slip Events
This data plot (Figure 2) is a representative sample of many collected over several months, comparing the actual torque loads in the turbine drive systems with and without the WindTC.

This plot shows the results of a normal braking event on two turbines, one with the WindTC (blue solid line) and one without (red dotted line).  The aero-tips have deployed while the turbines are operating under partial power.

Note:
• Black line is zero torque
• Solid blue line is the torque with the WindTC
• Red dotted line is torque without the WindTC
• Dashed blue line is nominal torque
• Dashed red lines are standard torque limiter settings
• Dashed maroon and purple lines show low-speed shaft speed

Without the WindTC, (dotted red), there is a large uncontrolled torque reversal at 75 percent of nominal turbine rating followed by a series of torque reversals back and forth over the zero torque line. The turbine equipped with a WindTC, from PT Tech (solid blue line), shows the initial reverse torque spike being absorbed at 40 percent of the nominal turbine rating.  More importantly, the slight reverse torque slippage in the WindTC dampens the torsional vibration so effectively that no additional reversals are recorded.

Forward Slip Torque Event: The NEG Micon NM 48 is a two-speed turbine that is not equipped with any torque limiting device. This plot (Figure 3) shows the comparison during an upshift event of the two turbines.  The generators are operating at low speed.  As wind speed increases, the low speed generators are disengaged, and the wind turbine speeds up as the high speed generators contactors engage.

Note:
• Black line is zero torque
• Solid blue line is the torque with the WindTC
• Red dotted line is torque without the WindTC
• Dashed blue line is nominal torque
• Dashed red lines are standard torque limiter settings
• Dashed maroon and purple lines show low-speed shaft

The turbine without the WindTC protection sees a torque spike of 200 percent when changing from one set of contactors to another.  The turbine with the WindTC is protected from this spike at its 150 percent setting and also prevents significant additional oscillations that are potentially damaging, even though they don’t cross the zero torque line.  

Conclusion
The Phase II testing proved the effectiveness of the WindTC’s ability to reduce the magnitude of both positive and negative transient torque spikes in the drive system.  It also proved its effectiveness at dampening any additional torsional reversals after the initial slip event.  As a result of these findings, the wind farm has initiated a program to retrofit their NEG Micon NM48 750kW wind turbines with the WindTC. Additional testing on other turbines has shown that torque reversals are not unique to the NEG Micon or to fixed pitch two-speed turbines. 

Larger, more current generation wind turbines up to 2MW have been monitored in the field with the same methods and have shown dramatic torsional reversals during transient events (Figure 4 and Figure 5).  Blade pitch systems reduce braking shock load events but damage still occurs with sudden curtailments and e-stops.  These events are much less common but they are significantly larger in impact due to the increased size of the turbine’s rotor and generator. 

AeroTorque will be releasing more data this fall on their work with larger turbines, as they have a full summer of new installations and monitoring. To control the life of your gearbox, you must control the loads that goes through it.  An asymmetrical approach to reducing these loads in the highly dynamic drivetrain of a wind turbine is an important way to do just that. 

When blade maintenance or tower inspection is required, there are a number of ways to get the work done. Some wind farm owners have maintenance contracts with the original installer of the turbine; some hire an outside maintenance company to do the work and others elect to perform the work themselves. One thing they all have in common however, is the need to keep the turbines operating at maximum efficiency. And to do that, they need to be regularly inspected and maintained.

A current trend among many wind farm owners is to establish a scheduled preventative maintenance program where they inspect and maintain all of the turbines and blades on a farm instead of waiting until an individual unit needs repair. That way operating efficiency is maintained, shutdown time is minimized and the likelihood of major problems that require shut down for extended repair in the future is greatly reduced.

While some methods of accessing blades and towers like rappelling or rope access or suspended scaffolding are great for inspecting and maintaining one turbine, the time to setup and rig the equipment to work on just one turbine or blade each time, then reposition it at another turbine location can be quite time-consuming, and costly.

For applications requiring access to multiple tower locations, a truck-mounted aerial work platform is usually a better alternative. They are more productive and safer to use than most forms of overhead access and they are available with a wide variety of working heights and platform capacities. Bronto Skylift machines, for example, are available with working heights up to 340 feet and horizontal outreach to 102 feet. They also feature platform capacities up to 1,500 pounds so that technicians can conveniently carry their tools and parts directly to the overhead area. Figure 1

Although aerial work platforms are ideal for wind farm applications, they are not inexpensive to purchase. A machine capable of reaching the top of 90-meter towers can cost as much as $1 million or more, making them a huge investment for most farm operators or maintenance companies. The good news is that aerial work platforms can be rented from a number of companies in locations throughout the country. And, because of the machines’ ability to be driven over the road, where machines are not available locally, they can be quickly transported to your site when needed.

Most rental companies provide their aerial rental customers with a dedicated driver/operator to transport, set-up and operate the machines on the job site. Some companies even offer certified technicians with experience in tower and blade inspection, documentation and repair to do the work, or work alongside other personnel provided by the wind farm operator or the turbine or blade manufacturer. Most rental companies will also offer operator training for other personnel to enable them to use the equipment safely.

Aerial work platforms feature a platform or “cage” mounted on a telescoping boom that is affixed to a turntable on the truck chassis. They are operated and positioned directly from the platform to give operating technicians a greater degree of control, and, unlike platforms suspended from overhead cables, they are not as susceptible to wind forces. Operators can quickly position themselves close to the blades and easily maintain that position while working. Figure 2

Most aerials are also equipped with electrical, pneumatic, hydraulic, and water lines that run inside the telescoping boom from the chassis on the ground to outlets in the elevated platform. These outlets allow technicians to operate powered tools and washers directly from the platform. This saves time and is much safer as it eliminates lines or hoses running down from the overhead platform to ground level and reduces the chance of accidental contact by workers or passing vehicles. In addition, because of the design of the platform, the extensive network of guardrails that surrounds the operator and technicians adds considerably to the safety of the operation.

Aerial platforms can be set up at or near the base of the turbine and, with the touch of a button, outriggers are automatically extended and positioned to level the machine. The operator and technician then enter the platform and the boom begins its ascent. The time from arrival at the site to being fully elevated at the overhead area is usually less than 15 minutes. Once set up, aerials are able to reach almost everywhere on the tower from a single location, they don’t have to be constantly repositioned. On a multi-tower site, this can save considerable time and money in set-up costs alone.

With higher productivity and increased safety, truck-mounted aerial work platforms are being used more and more to access overhead areas on wind farms. And, with the ability to rent or lease them from a wider variety of sources around the country, they are quickly becoming the preferred method for inspection and maintenance of wind turbines and blades nationwide. 

The debate rages on about whether torque or tension is the best method to preload a fastener, and it is nearly as controversial as the age-old question of which came first… the chicken or the egg?

Each side argues that their method is the best. However, the real question, and true heart of the matter, is whether torque or tension is the best method for each job’s specific bolting application.

“You want to analyze your bolted joints to determine when you need torque or tension,” states Bill Washington, director of business development at FASTORQ. “I can tell you that on many flanges, they are over-designed, and torque is fine in many cases. However, you have to use tensioners to get the bolt load you need on critical flanges.”

Bolt Load
To review, torque is used to turn a nut to stretch a bolt and provide clamping force. It is usually done with a manual, hydraulic or pneumatic torque wrench. Tension produces stress, or load, on a fastener. The result is strain. This is where the material in the bolt wants to return to its original state. This can be achieved with a hydraulic stud tensioner that directly pulls the desired bolt load into the fastener and with a nut turned down to hold it. Both methods work to achieve bolt load and have their pluses and minuses. Figure 1

“When proper preload is applied and maintained, regardless of the equipment used to load the bolts in a joint, the bolt cannot fail from fatigue, because it will experience no change in stress,” according to Washington. “Anyone can cause any fastener to fail by simply over tightening or under tightening it.”

“The problems caused by incorrectly loading any system can be catastrophic,” Washington says. Whether it’s a piping flange in a refinery that ultimately causes a fire or a wind turbine that comes down, “turbine and all,” when a bolt in the hub hasn’t been properly tightened, proper bolt load on critical joints is essential. The bolted joint can be the “weakest link.” Figure 2

The best way to avoid catastrophic results from bolt load failure, Washington explains, is to follow proper operation procedures and work practices when using torque and by using load indicating washers or an ultrasonic extensometer to measure preload. However, in the absence of a way to measure preload, then tension may be the best option.

Torque
“Torque is OK, and is widely used in a lot of applications,” Washington says. “Torque is a relatively inexpensive option to tighten bolts, and it can do well on most jobs.”

Yet, the problem with applying torque, notes Washington, is people must understand all of the things that “get in the way of applied torque resulting in desired bolt load.” This problem can be summarized as “K” Factor or nut factor.

“The big problem with torque is that we have a lot of things going on,” Washington explains. Several factors make up the “K” Factor, including contaminants, rust, lubricant, bolt fit, washers and surface condition that could allow embedment. All of these factors, and more, will impact resulting preload.
“The problem with ‘K’ Factor is that you can try to predict it the best you can based on experience… but it is an experimental factor, which means you can’t get ‘K’ unless you’ve already tightened the bolt and measured the bolt load. Now you know, after the fact, what ‘K’ was and not what it will be,” Washington says. “The problem is, if you don’t consider it at all, you are certainly going to be wrong.”

Even with a good procedure utilizing a crisscross pattern to apply torque in steps at 30, 70, 100 percent of final torque with a 100 percent circular, it takes time and still may not be accurate. “If a person takes shortcuts,” Washington says, “You can pinch a gasket and actually cause the joint to leak.” Figure 3

As a way of overcoming “K” Factor problems, bolt preload can be measured by using an ultrasonic extensometer. The biggest problem with these machines is that they are very expensive and many people do not know how to operate them. Another less expensive and simpler option to accurately measure bolt load is by using a load-indicating washer, also known as a Direct Tension Indicator (DTI). Washington explains that a person can be trained to use a load-indicating washer within 30 seconds.

Despite several conditions that can significantly affect bolt load when using torque, some situations call for it, such as when there is limited clearance and stud tensioners cannot fit. Since only one nut can be turned at a time, Washington encourages users to find a strong and fast torque wrench, such as a SpinTORQ, which minimizes the time it takes to complete a bolted joint.

“Time is money. For mounting blades to hubs, you may want to use a torque wrench. By using a standard hydraulic torque wrench to torque those bolts, it can take a lot of time,” Washington says. “Using a SpinTORQ to torque those bolts takes less than on fifth of the time.”

Tension
“Tensioning systems compared to torque wrenches can cost 10, 20, 30 times as much as torque wrenches. So it’s a big investment for stud tensioners, “Washington explains. “If you have a problem flange, and it is critical that your bolt load be evenly distributed, you want tensioning.”

When numerous bolts need to be tightened on a flange, tensioning is the fastest and most reliable way to achieve even bolt preload, according to Washington.  Tension can reduce or eliminate elastic interactions depending on the coverage, minimize or eliminate potential over-compression of gaskets and eliminate many of the obstacles torque has when achieving desire preload. Figure 4

“If maintenance is to be done and you need to get a unit back online, it’s really just a matter of how fast you want to get the job done,” Washington says. “Bolting is one of those things that gets in the way of getting things back online quickly.”

With fixed and variable stud tensioners that run at 20,000 psi, it’s difficult to fit the load cells side by side (due to their size), and they will need to be screwed on by hand. Fifty percent coverage of the bolts is typical, anything less and people start to run into the same problems they have with torque, states Washington. Elastic interactions, along with uneven bolt load can occur. With these type of tensioners, the first half of stud tensioners need to be set at a higher tension to compensate for the residual load from the second half of the tensioners that are put on the flange. Figure 5

Additional downsides with stud tensioners include: higher load on the first pass can cause over-compression of gasket material, additional bolt length is required, they are an expensive investment, most fit only one size bolt and the applied preload doesn’t always guarantee desired clamping force.

Another alternative to fixed and variable stud tensioners is the ZipTENSIONER. One hundred percent coverage is possible with these tensioners on the same side of the flange, and they reduce residual load problems. Also, these stud tensioners remove the tedious on and off threading involved with positioning conventional stud tensioners on a flange. They are able to do this since their reaction nut is a ZipNut®, which was originally designed for NASA for use on the Space Shuttle, International Space Station and to repair of the Hubble Telescope. ZipNut has spring-loaded thread segments that slide down the bolt. When the tensioner is engaged, they grab onto the bolt, lock in mechanically and then can slide back off without having to thread anything on or off. Figure 6

“The ZipTENSIONERs are different. The time savings are huge. You can reduce the time it takes to tension a flange by 80 to 90 percent. We go to a higher pressure range of 30,000 psi; we’ve reduced the load cell area and we can get 100-percent coverage on the same side of the flange,” explains Washington.

“The ZipNut reaction nuts don’t cross-thread or have problems with the condition of the bolt. I can pull all of the bolts into tension simultaneously and be done. For gasket seating stress, it’s ideal because I’m evenly loading, with evenly distributed bolt load, the entire flange simultaneously.”

Contributing Factors
It is important for wind turbine design engineers to consider critical bolted joints and whether they should use torque or tension, Washington says. This matter should not be an afterthought.
“Engineers need to make sure that they allow enough room for the tools. Sometimes, they don’t always allow the proper clearances for these tools to be installed on a bolt and work properly,” according to Washington. “Many times that causes work-arounds.” Figure 7

Other factors that make a difference in torque and tension are use of lubricants and the reuse of nuts and bolts. “A good lubricant with a sufficient amount of solids is always critical, whether you are torqueing or tensioning. Any old lubricant is not OK. You want the nuts to spin as freely as possible on the bolts to obtain the load that you need with the required torque,” Washington advises. “You also want a lubricant that allows you to have enough residual on a bolt so that there is something there between the nut and bolt when you are ready to break it loose.”

He also warns that reusing nuts and bolts in not a sound idea unless it can be assured that their integrity has not been compromised over time, since it can effect their performance.

The Winner
So, which method is the clear winner? Just like the chicken and egg question, it all depends on perspective.

“You’ve got to make some decisions about torque vs. tension based on performance requirements and budget,” Washington explains. “If you base your decision on torque vs. tension strictly on budget, irrespective of performance, and if you have a problem flange, you’ll blow the budget and then some trying to fix it.”

Mainly, it is necessary to understand your needs, according to Washington. If you have a lot of bolts to tighten, torque with a high quality torque wrench and load indicating washers is a good way to go. However, if you have a critical joint and you want the most accurate results and even bolt load, tension is worth the money, especially with stud tensioners that are designed to be efficient and save time.  

The practice of Mini-Grid Commissioning, utilizing mobile temporary utility systems to create a simulated power environment, is giving developers nationwide more flexibility and confidence in meeting legal and financial commitments during a facility’s commissioning phase.

Despite a range of ever-present risks in our industry—from the price volatility of a kilowatt hour (kWh) to the changing political and regulatory landscapes all of the industry’s players must navigate—there is no room for risk, when it comes to a project’s commissioning phase.

The Potentially Steep Price of Missed COD
Project stakeholders in a field’s construction phase still are acutely aware of the critical, finite time frame between two contract milestones: The Interconnection Agreement (ICA) date, whereby your system is tied into the power grid, and Commercial Operation Date (COD), which is a contractual obligation within your Power Purchase Agreement (PPA).  It is the second date—the promise that you’ll be able to fulfill your obligation to whatever party is buying the new facility’s power—that may cost you when failing to commission on time. 

If your field cannot deliver power by its COD, it may be liable for damages—first on that actual date, and again for each day beyond that power is not being produced, for the amount under the prescribed terms.

Because potential damages can run into high dollar amounts, project stakeholders must always be prepared to review the scale of their facility’s construction and commission, to ask themselves: How confident am I that I can commission each of my turbines comfortably prior to the COD date?  In addition, there are financial incentives to commissioning early. So missing the COD means not only punitive measures but significant opportunity cost.

There are also investor relations and tax implications of not meeting this commitment. So as wind energy development scales nationwide, developers and contractors are looking for new ways to better manage the risk of not meeting their COD commitments.
 
What is Mini-Grid Commissioning?
This practice developed from the desire of project stakeholders, both to avoid the risk of missing the COD within their PPA, and to capitalize on the financial returns of early completion. Mini-Grid Commissioning involves creating a simulated environment with mobile temporary utilities—for the purposes of testing and successfully commissioning a turbine. This enables a developer to complete all testing and commissioning prior to the grid actually being energized. In this way, if, say, the transformer you were expecting doesn’t arrive or your interconnect does not go as planned, the potential bottleneck in testing and commissioning equipment is reduced or eliminated.

Mini-Grid operation requires the provision of mobile generators to power critical equipment and infrastructure, a suitable load bank, a circuit breaker, a transformer and supporting equipment. Regarding actual field infrastructure, the mini-grid is usually used to:

• Energize the circuit to confirm the installation performance
• Test the pad mount transformers, and
• Start energizing the turbines themselves through this auxiliary power network—load testing and commissioning while also managing the subsequent power created by this test environment.

Each project will vary based on the dynamics of the site and turbines, as well as the specific commissioning requirements each manufacturer demands. Typically this Mini-Grid will run the system for 12-24 hours, commissioning 2-4 turbines at the same time. The Mini-Grid can be set up in a number of locations on the project site, and be managed by a small crew. As with any use of external resources, close communication, coordination, safety compliance and pre-project planning are all essential.
 
Budgeting Mini-Grid into Upfront Construction Planning
A number of wind energy developers are building this practice into every construction plan, to ensure that there is nothing left to risk in relation to the efficiency of planned tests and commissioning. Others use it as a stopgap when unforeseen circumstances threaten their commissioning timelines. It is a useful technical solution, no matter which school you subscribe to, as long as you recognize that the economics change slightly from one scenario to the other. Figure 1

When considered as part of the construction plan by default, cost planning can become more accurate and predictable. Mini-Grid Commissioning teams can be planned in advance. Availability of a team is guaranteed. The provider gets to know the intricacies of how the developer and contractors prefer to manage their projects and work together. And because nothing is rushed, the logistics of the team and its assets are more conventional and cost-effective. These teams, and the process in general, represent a tiny fraction of the developer’s construction budget. But adding them to every new build does add a new cost, however marginal.

Calling in a Multi-Grid Commissioning team only as a one-off crisis management tool avoids adding a recurring cost to all new projects, but the tradeoff is that you will likely be fighting other developers on the team’s availability. There aren’t many companies that provide this service, and developers who are planning ahead are always at the front of the queue. Either way, with the big-picture risk and potential opportunity costs, it is obvious that this practice has gained traction.

COD Commissioning Risk Triggers
2013 has been a busy year for wind energy developers. The PTC and ITC extensions—a moderate domestic economic recovery and improving technology costs and performance—mean steady activity. At the same time, low energy cost of competing fuels such as natural gas and the realization that tax credits won’t live forever mean that many are cautious. This push-pull has given 2013 supply chains more volatility than in the previous year. Manufacturers are cautious and many have slowed production. Some developers have experienced slow delivery of wind towers and turbines. These types of delays can happen to anyone. In addition to slow delivery, a developer’s COD can be put at risk by:

• Late delivery of transformers
• Receipt of faulty equipment or equipment that fails factory testing
• Missing your interconnection cut-in with the utility
• Your project’s substation not being energized on-time
• Utility power isn’t available for whatever reason

Whatever the cause, when your interconnect date and COD are uncomfortably close together, you only have so many options. And when you look at the economics of this early phase of your project, there are many reasons to keep Mini-Grid Commissioning in mind as an option as projects move forward.

Other Economic Impacts
Punitive damages that are avoided constitute a “big stick” waved to those who are in danger of missing her COD. But along with that stick come quite a few carrots! Developers and contractors who consider Mini-Grid Commissioning to be a reasonable standard protocol (as opposed to a crisis-management process) are placing a premium on the ability to fast-track commissioning.

After all, Mini-Grid Commissioning means faster commissioning. Faster commissioning also means those who might wish to sell their facility can get their investment out just that much more quickly (every bit counts, especially when it’s your money). Faster commissioning delivers power to market more quickly, accelerating project ROI in general. In fact, commissioning all manufacturers’ equipment onsite by the interconnect date can enable a field to begin saleable generation prior to its PPA taking effect. This may mean an extra few weeks or even a month of bonus revenue. In addition, developers must consider the importance of maintaining investor confidence. Once a commitment is made to add a certain number of kWh to the market, it is set in stone. Figure 2

In addition to creating a faster way to construction completion, systematically accelerating commissioning timelines through Mini Grid Commissioning also means quicker access to tax incentives, which can be a major motivator.

If you are a developer of wind power assets, you are aware that on January 2 this year, President Obama signed into law an extension of the federal PTC for renewable energy projects breaking ground before January 1, 2014. A similar extension of the ITC was also enacted. As a part of the ITC, developers are awarded 30 percent of their construction cost upon completion—and then earn 2.2 cents per kWh for 10 years through the PTC. The cost of bringing in a Mini-Grid Commissioning team is marginal and considered part of a facility’s construction budget, so 30 percent of the cost of Mini-Grid Commissioning goes away almost automatically. There are also local tax incentives to be had, the details of which depend on facility location.

Help Wanted: OEM Commissioners
The wind energy generation industry’s 10 or so major manufacturers of equipment only have so many people dedicated to the commissioning of their equipment. It’s not that global players such as Siemens, GE and Vestas don’t have the manpower or partners. The real problem is that since investors and developers tend to respond to the same market and regulatory drivers, projects tend to come in waves. Since so many project participants must overcome the inability to get a busy rep on site, their schedules become risk “endangerment by bottleneck.” Mini Grid Commissioning helps you give the manufacturer a larger time window within which you plan your investment so that you are not scrapping for their time at the last minute.

Vendor Selection Criteria
Most developers don’t keep specialized Mini-Grid Commissioning teams mobilized, necessitating work with an outside specialist. The most important criterion to remember when you explore your options? Experience. Your facility commissioning schedule carries not just significant financial, but also strategic, importance.

Instead of gambling on a partner with little experience, find someone who has done this before with multiple wind facility start-ups. Ask tough questions. Nobody wants their project to be a part of someone else’s learning curve. The provider should be familiar with and prepared for the process and the potential problems—such as the power spikes generated from the turbines and miles of underground cable. You want someone who can speak the manufacturers’ language up front to find quick solutions as unforeseen events arise. And have them verify results in the field over time through multiple project references.

Conclusion: It’s Good to Have Options
2013 is the perfect year to use Mini-Grid Commissioning as a tool to improve project profitability and confidence. It’s a new trend—not yet a part of every major developer’s construction plans. That means you can find a crew when you need one.

But at the same time, it’s not so new that it’s not accepted by the mainstream as a proven technical solution to a critical issue. A developer could turnaround dozens of projects without ever needing Mini-Grid Commissioning as a way to ensure COD compliance—and never miss out on the benefits of systematically commissioning equipment early. But it’s still a solid, proven option for both ensuring operational milestones and strengthening financial performance through the intelligent use of external resources. Whether or not you choose to make Mini-Grid Commissioning a part of your future construction plans, it’s always good to know your options—and empower your organization to more aggressive operational risk management whenever the chance presents itself.  

More than 2,000 miles from the continental U.S., Hawaii residents have learned the benefits of being self-sustaining. If a good or service cannot be produced locally, then it has to be shipped in. There is much planning, organization, and expense associated with importing these conveniences of modern day living to the islands’ nearly 1.4 million residents.

This holds especially true with regards to bringing power to the islands. If it’s not locally produced, then fuel sources such as diesel, gas and oil are shipped in by barge. This harsh reality is behind the state’s aggressive clean energy policy. State law mandates that by 2030, at least 70 percent of Hawaii’s power comes from clean energy sources, 40 percent of which must be locally produced from renewable sources. With this policy in place, wind energy is beginning to figure heavily into the state’s energy policy. Figure 1

Harnessing the Wind
The Buckner Companies of Graham, N.C. spent the last year with its 660 ton Terex CC 2800-1 NT lattice boom crawler crane helping to erect wind turbines on Oahu and Maui for RMT, Inc. of Madison, Wis. and project owner, First Wind of Boston, Mass. The Kawailoa Wind project consists of 30 turbines on Oahu’s North Shore, generating 69MW of clean energy, enough to supply 5 to 10 percent of Oahu’s annual electric demand, and saving 300,000 barrels of oil each year.

Maui’s Kaheawa Wind II project adds 14 turbines and 21MW of power to the existing wind farm nestled on a ridgeline of the West Maui Mountains. In total, the Kaheawa wind farm generates 51MW of wind-generated clean energy—enough to power 18,700 homes annually. Figure 2

The Kaheawa Wind project is the first wind project in the U.S. with a detailed habitat conservation plan. A staunch believer that an environmentally friendly power source should be built in an environmentally friendly way, First Wind used the plan to be sensitive to the habitat and wildlife needs, while fulfilling the island residents’ need for clean energy.

This presented Buckner Companies and RMT with some interesting on-site challenges during turbine construction. However, these were met through the use of its new Terex CC 2800-1 NT.

Narrow Capacity
The Kaheawa project consisted of 14 turbine pads and most had one thing in common. “The pads were extremely small, and only one site (pad six) had enough space to assemble the crane,” said Jay Lusso, technical services representative for Hayden Murphy Equipment Company. Hayden Murphy is a Terex Cranes distributor who was on site to assist with CC 2800-1 NT rigging and derigging.

The plan, according to Kevin Long, Buckner’s heavy lift project manager, was to erect a turbine and then move the crane under its own power to the next turbine pad without disassembling it. There was only one catch. The roads were extremely narrow. “The roads were only 20 feet wide, which meant a conventional 660-ton capacity crane was too wide to navigate the roads,” Long said. Lusso added, “We could not disturb the property at the sides of the road, since the grasses and habitat were protected.” Figure 3

Conventional 660 ton cranes measure up to 32.5 ft wide to the tracks’ outside edges. Long admitted that the company considered completing the Maui project with a 440 ton crawler crane to navigate the tight roads. In the end, however, “we wanted the higher capacity crane to deal with wind challenges, and we had the narrow track crane on the island,” he said.

Whereas the track footprint of the conventional Terex CC 2800-1 measures over 32 ft, the track width of the Terex CC 2800-1 NT is only 17.4 ft, allowing Buckner’s crews to navigate the narrow roads. Even with the narrow tracks, the crane still offers the high lift capacities customers expect from a 660 ton class crane. Large 16.4 ft long x 4.6 ft wide front/rear outrigger pads work in conjunction with two hydraulically operated side 9.8  x 7.9 ft outrigger pads to give the stability required for lifting heavy loads.

Construction of the 1.5MW turbines on Maui required 276 ft of main boom with a 39.4 ft fixed jib. The crane’s upper structure was equipped with 198 tons of counterweight for the maximum 70- ton lifts to erect the turbines. With constant wind speeds on the West Maui Mountains often reaching 17 mph, RMT’s crews appreciated the strong load chart of the 660 ton crane and its maximum wind load rating of 21.9 mph. “We faced consistently high wind speeds on the project, and the CC 2800-1 NT efficiently and effectively handled the wind,” Long said. “Having the higher capacity crane gave us more working days on the project.”

Once a turbine was finished, crews moved the crane to the next pad. “It was about 100 yd between each turbine pad,” Lusso said. The CC 2800-1 NT’s remote control aided in safely moving the crane from pad to pad. Figure 4

If the narrow roads weren’t challenging enough, the steep grades of the mountainous terrain added to the project’s difficulties. “We were traveling unusually high grades of up to 17.5 percent,” explained Long. With its maximum 10- degree gradeability, the Terex CC 2800-1 NT efficiently handled the steep grades, and its Quadro track drive helped with maneuvering by allowing the tracks to counter rotate to make tight turns.

RMT’s crews started at turbine pad site six and worked their way down the mountain to pad 14. When finished at turbine 14, they moved the CC 2800-1 NT up the mountain without disassembling it to pad one and worked their way back to pad six. Figure 5

Once back to turbine number six in May, they had enough room to disassemble the crane for transport to Oahu. Transport of the crane to and from the port and between islands was arranged by locally owned general/mechanical contractor American Piping & Boiler Co. (APB), of Kapolei, Hawaii. “Moving between islands was logistically challenging, but APB did a fantastic job handling all of the arrangements,” Long said. Reflecting on the steep grade, narrow road width and ample capacity in a high wind application, Long marveled at the benefits offered by the CC 2800-1 NT. “That model crane is the only crane at that capacity that could do the project,” he said.

Mega Power
When using the narrow track crane at the Kawailoa Wind project on Oahu, Buckner noted one additional advantage offered by the CC 2800-1 NT—ease of assembly and disassembly. From June through mid-October, crews used the crane to build 30 of the larger 2.3MW turbines. “Because of the challenging site conditions, we had to assemble and disassemble the crane three times,” Lusso said.
Hayden Murphy was on site each time the crane was disassembled to offer support and consultation. Additionally, the same remote control unit used to move the crane from pad to pad, is also designed to assist with crane assembly. Figure 6

These large turbines required a maximum lift capacity of 105 tons. The crane was equipped with full counterweight, 334.6 ft of main boom and a 39.4 ft fixed jib offering up to 10-degree offset.

Even with the longer boom configuration and 50 percent higher capacity lifting requirement, Buckner did not need to equip the crane with its optional superlift for the project. Long reports this significantly improved crane assembly and disassembly efficiency. “The total disassembly and reassembly process took two to three days,” he said. “If we would have needed the (superlift) derrick, this would have added another full day to the process.”

The CC 2800-1 NT allowed RMT’s crews to efficiently install the larger wind turbines on Oahu as it did for the smaller turbines on Maui. With the opening of these two most recent wind farm projects in Hawaii, the total of First Wind’s turbines operating on Oahu and Maui generate enough clean energy to serve over 40,000 businesses and homes. Figure 7

To ensure these turbines continue to harness the renewable wind energy at peak efficiency, Buckner will keep the Terex CC 2800-1 NT on Oahu for five years. The company has created a joint venture with APB, American Piping & Buckner, to assist with maintenance and service activities.

About the Terex CC 2800-1 NT
The Terex CC 2800 1 NT Crawler Crane offers a high return on investment and is among the most economical and versatile narrow track cranes in the 660 ton class. Using a selection of specially designed accessories, the crane is convertible from standard (CC 2800-1) heavy lift configuration to Narrow Track crane (CC 2800-1 NT) and back, providing outstanding performance in a wide variety of applications, including wind farm sites, where extra heavy load capacity is a necessity.

Recognizing the high potential of the onshore wind turbine market and the subsequent need for dedicated equipment in the 660 ton class, Terex Cranes developed the CC 2800-1 NT (narrow track) from the standard CC 2800-1 version to suit specific wind farm construction requirements. Equipped with its Narrow Track chassis, the Terex CC 2800-1 NT can be driven from one construction site to the next, even when access is tight, while fully rigged with counterweights, 334.6 ft main boom and LF 2 fixed jib, saving precious time and increasing productivity. Figure 8

The CC 2800 1 NT version is based on a conventional CC 2800-1, where the standard chassis (27.6 ft track width) is replaced with the Narrow Track Kit comprising of: chassis track with 5.3 m outer track width and front and rear outriggers, two 16.4 ft long x 4.6 ft wide outrigger pads for both front and rear outriggers, two side outriggers with 9.8  x 7.9 ft outrigger pads, counterweight suspension frame to lower the center of gravity and control system with remote control unit and full color graphic display monitor at the rear of the crane chassis. To provide stability and quick rigging times, both front and rear outrigger beams remain connected to the carrier.

The Companies Buckner Companies
With over 65 years of providing reliable, quality and safe services to the commercial and industrial markets, Buckner has earned its reputation as a nationally recognized leader for steel and precast erection and heavy lift cranes services. Buckner builds long term relationships with its customers based on confidence, trust and integrity. Offering exceptional project management, field supervision and experienced field crews, Buckner exceeds the client’s expectations safely, cost effectively and ahead of schedule.

For more information on Buckner Companies, visit www.bucknercompanies.com.

First Wind
First Wind is an independent wind energy company exclusively focused on the development, financing, construction, ownership and operation of the utility scale wind energy projects in the United States. Headquartered in Boston, Mass., First Wind focuses on developing and operating wind energy projects in the Northeastern and western regions of the continental United States and in Hawaii.

For more information on First Wind, visit www.firstwind.com.

Terex
Terex Corporation is a diversified global manufacturer of a broad range of equipment that is focused on delivering reliable, customer driven solutions for many applications, including the construction, infrastructure, quarrying, mining, shipping, transportation, refining, energy, utility and manufacturing industries. Terex reports in five business segments: Aerial Work Platforms; Construction; Cranes; Material Handling & Port Solutions; and Materials Processing. Terex offers financial products and services to assist in the acquisition of equipment through Terex Financial Services.  More information can be found at www.terex.com.