June 2010

While wind power inverter systems have traditionally used capacitors with application voltages around 500VDC, the trend today is toward higher-voltage systems. Film capacitor technology offers significant advantages over other technologies in these new higher-voltage applications due to improved life expectancy, environmental performance, and power handling capability. This paper compares both the mechanical and electrical characteristics of film and aluminium electrolytic capacitors, in terms of their ability to address the challenges for the designer of high-voltage power systems required in the very latest wind energy applications.

Wind power is a fast-growing market around the world, with higher prices for fossil fuels and concerns over environmental impact being two of the main driving factors. Furthermore, the improved efficiency of wind-power generation is also developing at a rapid pace. One element of this is higher voltages in generator systems, where the capacitors are actually located inside the converter.

As previously mentioned, many wind-power systems have used capacitors with voltages around 500VDC in the past, but today the “sweet spot” is in the range of 600-1350VDC, depending on the output AC voltage from the alternator. This is because higher voltages are increasingly used to reduce power loss in the alternator and converter of the windmill. Higher voltages allow lower RMS current for the same power. In this area, non-gas impregnated film capacitors offer significant technical advantages over previously used electrolytic capacitors. AVX power film capacitors are able to provide a real boost to wind-power stations, with extremely high capacitance values of up to 48,000 μF available. Figure 1

Controlled Self-Healing
One major advantage is the ability of film capacitors to overcome internal defects. The latest dielectric films used for DC filter capacitors are coated with a very thin metallic layer. In the case of any defect the metal evaporates and therefore isolates the defect, effectively “self-healing” the capacitor. As wind power systems are normally located in remote locations, this feature can significantly reduce ongoing maintenance costs and ensure higher efficiency of usage in the installed system. Although a quick search will show a number of “segmented metallized film technologies” on the market, they don’t all achieve controlled self-healing. Non-optimized segmentation can generate unexpected results, such as loss of controlled self-healing if under segmented or very low lifetime expectancy if over segmented.

With 30 years of experience in manufacturing controlled self-healing capacitors, AVX can claim extensive knowledge in this area. The main advantages of this technology are proven field reliability with zero catastrophic failures even under severe usage conditions, providing a competitive solution while maintaining the highest electrical and mechanical specifications, and long lifetime expectancy.

Over the last 10 years AVX TPC has developed a wide range of products that incorporate all the benefits of controlled self-healing technology. Ideally suited to all new energy applications, AVX is the first worldwide supplier of controlled self-healing DC link capacitors for windmill applications. The main power film series are FFVE/FFVI, FFLI, FFLC (dry technology), and Trafim (oil filled technology). These provide a wide range of form factors and capacitance/voltage options that cover most applications, with custom solutions available for specific design requirements.

Comparing Film vs. Aluminum
With today’s dry film technology the voltage gradient can reach more than 500V/um for discharge applications and 250V/um for DC filtering applications. These film capacitors are designed to CEI 1071 standards. This means they are able to handle multiple voltage surges of up to twice the rated voltage without significantly decreasing product lifetime. It also means that the designer need only account for nominal voltage requirements when specifying his system.

By comparison, due to the process technology, the thickness of aluminium foil used in electrolytic capacitors is key to reaching higher voltages. There is a trade-off, however: the higher the voltage, the lower the available capacitance. In addition, higher voltage (500V) electrolyte conductivity reaches 5kohms/cm compared to around 150kohms/cm for lower voltage versions. This also limits RMS current values to about 20mA per µF, compared to 1A per µF for film capacitors. A major requirement for DC link capacitors is their ability to handle ripple current. Here, film capacitors have a major advantage. Using aluminium electrolytics would require banks of several capacitors being used; and not because a higher capacitance value is required, but simply to handle the current. Using film capacitors would mean that the designer need only consider the minimum capacitance value required for the system. As a result, designs that use film technology frequently save space.

In order to reach the higher voltage requirements of the systems being designed and deployed today, it would be necessary to connect multiple electrolytic capacitors in a series. This would require balancing the voltage by connecting resistors in parallel with each capacitor because the IR (insulation resistance) of each individual device will vary. This results in an overall increase in direct leakage current, equivalent to lowering the overall IR of the system.Figure 2

Another concern in using electrolytic capacitors would be that, if a reverse voltage or over voltage higher than 1.5 times rated voltage occurs, it can cause a chemical reaction. Should it last long enough the capacitor may suffer catastrophic failure, to the extent of developing a short circuit breakdown or suffering a pressure release where the internal electrolyte may evaporate. To overcome this the system designer would need to connect a diode in parallel to reduce the potential problem. So, although it is technically possible for aluminium electrolytics connected in series to attain the necessary higher voltage levels required by today’s wind energy applications, the circuit design can be problematic, requiring the use of additional components or protection to ensure successful operation.

Surge voltage is another important consideration. The capability of aluminium electrolytics to withstand surge voltages is limited to approximately 1.2 times the nominal voltage. This means designers must take surge voltage into account when specifying these types of capacitors. By contrast, higher voltage film capacitors (above 1350V) utilize non-toxic organic oil filled technology and can operate up to 100kV. These capacitors, along with the dry film technology discussed earlier, can be considered environmentally friendly solutions because they do not use acids and therefore do not represent a risk to the system itself. Both types of film capacitors can also be stored without concern, as, unlike electrolytic capacitors, they have no “dry out/wear-out” mechanism.

Life Expectancy
Ultimately, the main advantage of film capacitors over aluminium electrolytic is life expectancy. Our internal data shows that AVX controlled self-healing DC filtering capacitors exhibit a maximum capacitance drop (ΔC) of just 2 percent after 100,000 hours of operation. When added to the fact that, compared to aluminium electrolytics complete device failure is very unlikely to occur, it means that during the full lifetime of an installed wind power system it will not be necessary to change the capacitors. This represents major maintenance savings for the user.

Since the early 1980s significant improvements have been made in the application performance of DC filter capacitors. This has been achieved through the use of either combinations of metallized films or by using different segmentations of metallization on the dielectric films. In fact, power film capacitor manufacturers continue to develop much thinner films and improved segmentation techniques, which will result in the continued release of superior performance devices. Figure 3

Summary
System voltages are continuing to increase in wind power/windmill applications. As these voltage requirements have risen they have passed the 600V barrier, which represents a major hurdle for aluminium electrolytics. These are limited in voltage and require connection in a series to successfully address this application, which can add significant cost in terms of space as well as being much more complex to design and install. Figure 4

Film capacitors (both dry and non-toxic organic oil-filled) offer significant technological advantages, including superior life expectancy and environmental performance, as well as the ability to handle the various types of “in-application” technical issues (over-voltage and reverse voltage) that can easily occur. Considering that these systems are often deployed in remote locations, and given the fact that they require minimal maintenance and downtime, the advantages of using of film capacitors in this type of DC filtering applications are very significant. As a worldwide manufacturer of capacitors for power electronics, AVX is in a position to offer products best suited to these applications. Indeed, since 1980 great improvements have been made in DC filter capacitor technology by a combination of different segmentation schemes of the metallization matched to specific film dielectrics. Both volume and weight have been reduced by a factor of 3 or 4 over the last few years. Figure 5

As a result of these key developments, several families of products have been generated over a wide range of capacitance values as represented by the AVX product families FFB, FFV3, FFVE, FFLI, FFLC. All of these products are widely used by AVX customers due to the advantages that they offer.For higher volume applications customers will often request a capacitor with specific characteristics tailored to the circuit. Again, AVX offers this type of solution, based on our long-time experience of capacitor design/manufacture for power electronics, typically producing more than 500 specific design studies each year. AVX also offers full design support in order to devise the optimum performance solution for a new project. 

Driven piles can be a cost-effective foundation system for some wind tower sites underlain by loose or soft soils, or mine spoils, which can provide insufficient bearing capacity and excessive settlement. The piles are driven around the perimeter of the tower foundation to resist the overturning moment by means of compression and tension loads. Driven piles may be slightly battered outward to resist lateral loads. Since driven piles do not require predrilling, they can be driven into a contaminated soil profile without producing spoil that can require costly removal.

Driven pile types include steel H-piles, pipe piles with concrete fill, precast concrete piles, mandrel driven shell piles, and combinations of the aforementioned. The type is chosen depending upon design capacity, drivability, and material costs. Typical pile size ranges from 12 to 30-inch equivalent diameter and typical design capacity ranges from 50 to 300 tons. The piles are designed for both the required structural capacity and stresses incurred during driving. Steel piles can be provided with epoxy coating when installed in corrosive soil environments.

Piles are typically driven with crane-mounted fixed or swinging leads and an impact pile hammer or vibrator hammer. In general, crawler cranes with capacities from 50 to 150 tons are used. Impact pile hammer types include air, diesel, hydraulic, and drop (gravity), and they provide rated energy from 25,000 to 200,000 ft lbs. The drive head contains a cushion material that is placed between the hammer and pile to prevent damage to the hammer and pile. The drive head also keeps the pile centered under the hammer. Vibratory hammers can also be used to drive piles. Vibrations from any small- to medium-size hammer will generally not harm adjacent structures in good condition. This concern is typically not an issue with wind tower foundations since wind farms tend to be remote or not adjacent to existing structures.

Pile foundation design is based upon an understanding of the hammer-pile-soil interaction during installation and the superstructure pile-soil interaction after construction. Piles must be installed to provide the required foundation behavior with consideration of the feasibility of pile installation controlled by an understanding of the hammer-pile-soil system. Consideration of pile installation in general can be characterized by the pile hammer as a driving energy source, the pile as a transmitting element, and the soil conditions as a resistant force to pile penetration. The pile driving behavior can be simulated by using wave propagation theory as an analytical tool. The analysis can predict the required driving resistance for a specified design pile capacity and a selected hammer-pile-soil system.

Quality control for driven piles includes logging the number of hammer blows per foot of depth. By monitoring the resistance to driving, the pile hammer acts as a measuring tool as well as an installation tool. Full-scale compression pile load testing and/or tension testing is typically performed on one or more production piles to verify the pile driving criteria. If a vibratory hammer is used to drive the pile, verification of the final seating criteria can be accomplished with an impact hammer. Vibratory hammers can be used for final driving criteria with field verification of penetration rate and horsepower, supported by pile load testing. Additional dynamic testing can be done to verify the performance of the pile driving in lieu of additional pile load testing. Two strain transducers and two piezoresistive accelerometers are attached three feet below the top of the pile to determine transferable energy, maximum pile stresses, and to estimate pile capacity during pile driving. Software can be used to further evaluate static pile capacity including relative load distribution along the pile length and toe at a specified pile depth.

Driven pile foundations have been used to support many types of onshore and offshore structures over the past 100 years, including recent wind tower foundations. Driven piles will continue to be an economical solution for future wind turbine foundations.

Despite a wind turbine design life of 20 years, the likelihood of a corresponding OEM warranty is remote, at least from a cost performance perspective. As a project comes off warranty and begins to age, owners should expect a steady increase in maintenance duration, cost, and resource needs. Not all project owners are prepared to take on the full work involved in maintaining their wind turbines, however, and in some instances come out of the warranty period with O&M teams that are understaffed and overworked. An OEM providing warranty service is able to easily supplement his operations staff to conduct retrofits and major repairs, yet once the warranty has expired the owner no longer benefits from this exclusive labor arrangement. Owners are instead left to perform O&M based on labor assumptions that had been distorted throughout the warranty period. For a project no longer in warranty, overtime pay can sometimes amount to a higher number than regular wages merely because the project is understaffed. Even when a facility has the technicians it needs to perform routine repairs, unscheduled maintenance puts a noticeable dent in a project’s bottom line.

In a conventional power generation facility, the number of technicians required to adequately operate and maintain the project is determined by a time-based distribution of the required operational tasks. For example, it may take three to six technicians to operate a 250MW combined cycle power plant at any given time, wherein each operator has certain tasks to perform. Staffing these projects is fairly straightforward, and plant outages where major maintenance is performed are handled by an “all hands on deck” approach and the utilization of subcontracted maintenance support.

What is the right number of technicians required to safely operate and maintain a wind project? A ration such as 1 crew: 20 turbines is common for the 1MW+ class turbines. This ratio might be lower when longer durations of scheduled maintenance are required on more complex turbines. Such “rules of thumb” are legitimized by many project operators today, but understanding how they are determined will help a project owner to more adequately staff wind projects. The operator might sum the estimated number of hours of daily, routine, and scheduled maintenance and divide by the number of available technician hours in a given month, typically ranging from 145-175 hours depending on the hours required for training, vacation, and personal time off. Inherently flawed, this evaluation process only provides the projected number of technicians necessary to meet the assumed hours of routine maintenance on the project. The approach of using industry rules of thumb or estimating personnel needs in this way does little to accommodate the resource needs of unpredictable downtime; something that can dramatically compromise routine service maintenance and troubleshooting duties. It is quite possible that a more conventional approach to operations and maintenance of wind projects—one similar to power generation facilities—could not only remove the scheduling issues of annual servicing, but also allow the project to achieve higher levels of reliability and availability.

To some degree operators are already moving toward a power plant format of conducting annual and semi-annual maintenance. After the initial 500-hour startup service, operators will try to work their maintenance schedules around annual weather patterns. Ideally these services are performed in anticipation of the windy and/or peak demand seasons in an effort to ensure high performance during these periods. To take it a step farther, if an operator is able to minimally staff a project that adequately addresses routine operations and minor repairs during peak wind season, then augmenting this same staff with qualified outside resources might be a better option for conducting annual maintenance during off-peak periods. The primary staff required to operate and routinely maintain the project is sufficient, annual maintenance is assured and completed in less overall time, and the turbine servicing is not conceded to repairs or troubleshooting. This approach also allows owners to mitigate the effect of unpredictable maintenance by choosing to move scheduled service and maintenance into a specified period and bringing in additional resources to complete this work.

As wind turbines have grown in size and capacity over the last three decades, the importance of reliability and technology innovation have been quite apparent. Even though these “Gentle Giants” look much like their predecessors of the 1980s—three-bladed, upwind configuration—technology improvements have been vital for the success of this vibrant industry. Every component and sub-component of the turbine, including airfoils, materials, structures, and sensor and control systems, have to be tested and evaluated prior to being deployed and accepted.

All engineered components and systems must go through a testing phase in order to validate the engineering assumptions made in the design, analysis, and manufacturing processes. The key questions pertaining to testing are why, when, and in some cases, how? As the wind industry has gone through its maturity phase, the trial and error days of going straight to the field and patching flaws in real time are hopefully long gone. This has been driven and enabled by both the fidelity of today’s engineering tools and computing capacity, as well as the requirement to certify components and systems to standards and the sheer cost of building and testing structures of this magnitude.

Wind energy components pose many challenges when it comes to testing and evaluation. Not only does wind have a series of unique components, the size of the components and the measurement requirements can make testing quite costly and challenging. Take, for example, a typical utility-scale wind turbine blade, which is 30-60 meters in length, weighs 10-20 tons, and is quite complex in shape. Today’s blades have matured immensely from the days when technology and manufacturing approaches were leveraged from other sectors. Modern blades are predominately made of a combination of glass and carbon fibers, resin, and balsa or foam. Each one these materials has to be certified and tested by their respective manufacturer, and must be brought together to design a blade which itself has to be certified. Airfoils are now optimized for aerodynamic and acoustic performance and tested rigorously in wind tunnels to ensure this performance under a variety of simulated field conditions. Moreover, the shape must lend itself not only to localized aerodynamic performance, but must also be coupled to the structural and manufacturing design, where the internal structure is designed to take advantage of the materials available and how they will be organized or stacked to develop a structurally efficient blade. Also, as part of the design phase the manufacturability must be continually evaluated to ensure that the blade can be manufactured to the specifications without the introduction of defects.

Although there will be several sub-scale testing phases throughout the engineering process, the entire completed blade must also be tested for structural strength and aerodynamic performance to validate the computer models and receive certification. These tests can be complicated and costly due to the size of the structure and the complex testing and loading requirements, which must replicate such things as the number of and magnitude of loading cycles that a blade will see over its 20 year life, in the case of fatigue loading. At this point it is key that the tested article is close to the final design, as it can cause significant cost increases and project delays to redesign, rebuild, and retest. Finally, these complex testing processes must also be completed as applicable for other components of a wind turbine, including gearboxes, generators, controllers, etc.

The tools used to develop and evaluate these designs are only as good as the data used to validate and improve the fidelity of the code. Additionally, the tools are only able to model the article to a certain degree of fidelity within a certain operational envelope, and many practical elements can diverge from the model in the as-manufactured, as-installed final product. The lessons learned and data gathered from lab and field testing, at both full-scale and sub-scale enables engineers to continually improve their designs, the result of which can be clearly seen in the viability and resilience of the wind industry.

The managers of wind farm projects face many challenges. Risk levels for EPC (engineering, procurement, and constructon) contractors are perhaps among the highest, as EPC contracts are often complex and exceptionally demanding. Not only does the contractor assume the risk for the entire schedule, but also the overall budget for the project. That’s not an easy task when you consider that the contractor is not only dealing with a client, but also managing a number of supplier resources that could be in multiple locations.

Logistical challenges are high. Any changes that must be made that affect the contract, or any problems that surface, can prove costly and could be devastating to the contractor. Remember that by agreeing to the contract the contractor is basically guaranteeing results and fully responsible for all outcomes of the wind power project, including all activities of the suppliers and vendors participating in the project. Penalties can be severe for any contract breaches, and there are no allowances for cost escalations in an EPC contract.

Contractors must build reliable networks and identify the most experienced resources. By concentrating on their core competencies they should bring in logistics resources that can provide the degree of experience and knowledge necessary for the contractor to meet all obligations. That includes each and every issue that will or could impact the success of the project—locally, regionally, and globally.

Why should EPC companies work with an experienced project logistics provider? Project efficiency. A reliable provider gives the contractor one point of contact, enabling tighter management of all transportation and logistics issues. The provider streamlines the monitoring and coordination of the logistics management process, including sourcing needs, and gives step-by-step accountability.

EPC contractors rely on their reputations, which depend on their ability to deliver on their contractual promises. They don’t want to compromise their reputation by working with unreliable sources. All the more reason why contractors should identify experienced partners they can trust and with whom they can build strategic alliances.

When contractors source wind power equipment, transportation is still one of the key factors to ensure the equipment arrives on time, intact and within budget. Because they don’t always have deep resources for truck, reloading, transshipment, and sea freight services, contractors often source from local forwarders. In many cases, however, the necessary equipment is not always available through those local sources, which means it has to be brought in from elsewhere. A global resource with wide sourcing capabilities can access the equipment and move it quickly and efficiently.

Due to its wide network, an experienced global logistics provider also knows the local and regional business habits and has an established “on the ground” presence. While local logistics or forwarder resources are familiar with their own areas, they may not be experienced enough to respond to last-minute problems or changes, especially those that require resources beyond their control. It is often a race against time, which is a luxury contractors and their clients do not have. Working with reliable logistics partners will be particularly important over the next few years, due to transportation capacity and equipment shortages. As we mentioned in an earlier issue of Wind Systems, general equipment availability and transport capacity will continue to tighten up as demand outstrips supply, adding more pressure to supply chains in the wind power industry. The fight for shipping capacity promises to be immense. It’s not just equipment and capacity challenges, however, but also a cost issue. Contractors have commitments to their wind power clients, who are on a fixed schedule, so time and speed are key components. Schedules must be met. If time is lost and penalties are incurred, the result can be failure and loss of credibility by the contractor in the wind power marketplace.

Within the next 12 months we expect significant increases in freight costs, adding more strain to an EPC contract. A logistics provider with access to and agreements with global transportation partners can make a positive difference. Just as contactors must be experienced in many areas, so must their logistics resources. Time is money, after all, and reputations depend on the success of each and every wind power project.

In the Los Angeles office of Korindo Wind, a division of Jakarta-based multinational Korindo, President Ricky Seung and his staff put in at least two days every single day. The first coincides with the workday at the Indonesian plant where Korindo Wind manufactures towers for wind energy development. The second is in line with business hours kept by the company’s European customers. Through it all they work with their main priority, contacts in the United States where most of the towers are installed.

Seung and his staff are working around the clock to fill the capacity of Korindo Wind’s manufacturing facility in Ciwandan. The ISO 9001:2000 certified plant can produce 800 towers annually, the equivalent of more than 2 gigawatts of installed capacity. Figure 1

Since 2006, more than 500 U.S.-bound towers have rolled off Korindo Wind’s highly efficient line, manufactured and delivered for some of the biggest global names in wind turbine manufacturing. That surprises some in the industry, given that the company’s primary competitors do not have to ship their towers across the Pacific Ocean. But combine less-expensive steel in Indonesia and lower operating costs in Asia with Korindo Wind’s comprehensive delivery package, and the company has built-in advantages that allow it to offer favorable contracts and highly competitive pricing for the U.S. market. Even compared to domestic suppliers, Korindo Wind’s landed price often is equivalent to or less than the cost of getting towers from a U.S. factory to the project site.

Cost is only part of the equation, though, says Seung, who adds that success in the United States requires three things: indisputable quality, unsurpassed service from plant to project site, and overall value to the customer.

Quality Counts
The value starts with quality. Every wind tower supplier claims it manufactures high-quality towers, and some can back it up, but few can prove it to the extent of Korindo Wind. “Quality, quality, quality,” says Henry Kim, wind quality manager. “Our overall quality system, including the quality management we do in our factory, is many steps above where most tower manufacturers are today. Since we are one of the few ISO certified tower manufacturers in the world, of course we meet those requirements, but we go beyond that at every stage.”

Kim has the qualifications and experience to pass judgment. He is an American Welding Society (AWS) certified welding inspector and, prior to joining Korindo Wind in 2006, he was the head quality manager at one of the company’s competitors. He is one of two quality managers in the Ciwandan plant, and together they have more than 20 years of experience in wind tower welding and fabrication. Figure 2

Their quality team does inspections at every single point of the process: raw material receiving, cutting, beveling, rolling, fit-up, submerged arc welding, blasting, painting, and assembly. Every step is documented with precision to ensure traceability. If there is a problem down the line, the company can pinpoint where it originated and address it immediately. Then there is a final shipping inspection before the sections leave the plant, a surveyor at the port ensures the integrity and quality of the sections has been maintained during transport, and another inspects them when they arrive in the United States.

Korindo Wind also has the credentials to back up its quality claim. The ISO certification guarantees customers that the company adheres to or exceeds the most stringent quality documentation requirements in the industry. Every Korindo Wind welder is AWS certified, and the 33-person quality team includes certified welding, coating and non-destructive testing inspectors.

Donald Rawson, an independent coatings inspector with a Level 2 National Association of Corrosion Engineers (NACE) certification, has inspected towers manufactured by four different companies. “I’d put their coating quality right up there with the top tower manufacturers,” he says. “The last inspection job that I went out on for them was probably the best I’ve ever seen.”

The real proof, though, is in the performance of Korindo Wind towers. In more than three years of manufacturing and delivery, there has not been one significant quality issue. That’s important, especially in a market that has shifted its focus from capacity and volume to quality and performance.

Upside of the Downturn
The recent worldwide economic downturn has impacted tower manufacturers that supply the U.S. market in obvious and often painful ways. Many have been forced to cut workers and others have had to halt production entirely. But there have been less-obvious consequences, as well. The level of quality that turbine manufacturers and developers are now demanding is an excellent example.

Even two to three years ago, turbine manufacturers couldn’t find enough tower suppliers to meet their needs, so capacity was the primary driver for placing orders. Those companies worked with anyone who could meet their volume demands. In general, tower manufacturers focused on completing as many towers as possible as quickly as possible, sometimes to the detriment of quality.

Today, with tower plants sitting idle and others with significantly reduced volumes, turbine manufacturers have the luxury of being more selective in supplier selection and are demanding higher quality and better service at lower prices. They also have time to more thoroughly evaluate potential suppliers for those attributes. Figure 3

Korindo Wind welcomes the new, heightened standard. “Turbine manufacturers have raised the bar to a new level, and we think it’s great,” Seung says. “Korindo Wind has been manufacturing to the higher level since the beginning, so we have no problems meeting the new expectations. We have tremendous confidence in our quality systems, our people, and our factory, so in many ways the situation makes our greatest strength even stronger.”

As other companies rush to play catch-up with their quality control systems, Korindo Wind continues to do what it’s been doing all along while gaining ground in research and development.

Efficient Systems
Korindo Wind has been exacting in the development of its operation from the beginning. The management team that runs the Ciwandan plant brought nearly 50 years of combined experience in wind tower manufacturing and quality assurance to designing the facility. That team has been a key to developing the quality that has become Korindo Wind’s calling card.

“Because of our depth of knowledge and experience in manufacturing towers, we were schooled in potential defects before we even built the plant. We’ve been able to take a pre-emptive approach and apply lessons learned to our layout and processes,” Kim says. “That saves time and money, and not just for Korindo Wind but for our customers, as well.” Figure 4

The plant features all the same high-tech, precision manufacturing, and measuring equipment that can be found in competitors’ facilities, and the quality team does ultrasonic and non-destructive testing on site. The plant’s linear production line is a model of efficiency. Raw materials enter at one end and completed tower sections exit the other with zero waste of time, effort, or material in between.

That allows Korindo Wind to produce more towers faster while maintaining its stringent quality requirements and, overall, charge less. And, with its location only one kilometer from the Port of Ciwandan, the company can cost-effectively ship towers anywhere in the world.

Consistent Delivery
Korindo Wind has never been late on a delivery, which carries a lot of weight in an industry where timing is everything and delays can cost millions a day. But it’s all in a day’s work for Korindo Wind; if the plant falls behind, the sections will literally miss the boat.

“We actually can’t be late because the vessels are scheduled in advance and we have to pay thousands a day just to have them sit in the port,” Seung says. “Whatever it takes to stay on schedule, we’re going to get it done.” Figure 5

To make sure that happens every time, Korindo Wind has developed a “comprehensive tower solution” that encompasses everything from sourcing raw materials to manufacturing and assembly to delivery duty paid (DDP) transportation. The company also owns and handles reverse logistics for the specialized H-frames that are needed to safely stack sections on ships.

With DDP the seller retains all risks and is responsible for all costs until the sections reach the agreed-upon destination. That can be a port, or because the company has strong ties with a domestic heavy hauler, all the way to the project site.

The logistics package addresses any concerns that customers may have about getting Korindo Wind towers to their U.S. project sites, according to General Manager David Choi. “It’s a full-service deal,” he says. “We provide the stacking frames and insurance, we coordinate the ships and handle the ocean freight, we take care of the duty and clearing customs, and we handle all of the port work and storage. It’s almost as if you’ve purchased from a domestic supplier, but you have the option of going to the port closest to your project site in the States or anywhere in the world.”

Choi says the logistics services also give customers certainty in what can be a highly volatile shipping market because Korindo Wind has negotiated a maximum rate with an ocean freight business partner. In addition, since all the towers arrive at the port closest to the site, domestic logistics and state-by-state permitting challenges are minimized. It also reduces inland transport costs, which can be substantial. Just to load a section and go down the street can cost $10,000 and, depending on the distance, can be as much as $50,000-$100,000 to haul it from a U.S. plant to a project site.

Another advantage that’s not quite so obvious is that all the sections arrive at the same time, ready to install. “It’s a project manager’s dream,” according to Seung. “He knows exactly when 20 towers will be arriving in the Port of Houston, for example, and he can schedule cranes accordingly. Those cranes cost an incredible amount for every day they are on site. With Korindo Wind, they’re not going to be sitting idle waiting for a top section that’s still on the line in a plant somewhere.”

Korindo Wind inspectors go over the sections at the port, and the company takes care of repairing any minor handling damage that may have occurred in transit. The company works with independent maintenance and repair providers to address issues once the towers are installed. “We do everything in our power to ensure customers get exactly what we’ve promised,” Seung says. “It all flows from Korindo, which has kept customers at the center of its corporate philosophy and vision more than four decades.

Strength from Strength
Founded in Jakarta in 1969, Korindo is a multibillion-dollar company comprising 14 divisions that serve diverse industries worldwide. They are engaged in timber and forest management; paper manufacturing and recycling; and the manufacturing of buses and trucks, parts for commercial vehicles, chemicals, palm oil, heavy vessels, and containers. They are also in trading, financial services, insurance, real estate development, logistics, and shipping. Overall, Korindo companies employ more than 30,000 people who export products and services to every corner of the world, including the United States, Japan, Korea, China, Singapore, Taiwan, Malaysia, India, the Middle East, and Europe.

In 2006 Korindo built the Ciwandan plant and entered the global wind energy market. It was a natural extension for a business that has long focused on sustainability and conservation. One of Korindo’s guiding principles reads that “We must not only provide great service and value for our customers, we must also respect and protect the environment.” Seung says every division is held to that standard.

“Sustainability is a general theme and way of doing business throughout all of Korindo,” he says. For example, when the timber division takes trees from a tropical forest, the company replants multiple new trees for each one harvested. “Anything that’s taken out and used is replaced by fivefold. Korindo has re-cultivated hectares and hectares of land, basically creating another forest in the process.”

Seung says that Korindo’s environmental and customer-friendly approach, financial strength, and multinational experience provide significant advantages in a tight market. “With Korindo behind us, we are able to take reasonable risks in putting together pricing and logistics packages that other suppliers can’t match and that help make projects feasible,” he says. “It also helps people understand we’re not a fly-by-night start-up. Korindo companies have decades of experience in heavy manufacturing, logistics, and other areas that are crucial to wind energy customers. We’ve brought all of that to bear in shaping Korindo Wind.”

Sliding electrical contacts used to transfer electrical signals or high current between two surfaces in relative motion can pose a significant maintenance burden. Traditional carbon- or graphite-based brushes used in most slip ring systems generate significant amounts of conductive wear debris, and the use of these brushes often results in electrical shorts to ground, reduced service life, susceptibility to contamination, low signal quality, restricted operating current, and the occasional fire. In the past there have been many unsuccessful attempts to solve these problems. Now, new military technology originally developed for the demanding needs of the U.S. Navy’s nuclear submarine fleet promises cleaner, longer-life brushes for wind turbine slip ring systems.

While many suppliers of “high performance” graphitic brushes add significant metal content to the brushes to improve the electrical performance, they are still burdened with the other known fundamental liabilities of carbon brushes. Some manufacturers have introduced what they term “metal fiber brushes.” These brushes are typically made from expensive gold alloy. These brushes address some of the shortcomings of carbon-based brushes, but since the fibers are oriented tangentially across the sliding surface and sequentially wear through the fibers in a transverse direction, they have relatively short service lives and are therefore not particularly suitable for high speed and high current applications.

Commercializing Military Technology
Since Navy submarines operate independently in remote regions and remain submerged for long periods of time, their electrical machinery demands high reliability with low maintenance. Several years ago the Navy teamed with the University of Virginia, HiPerCon, LLC, a Virginia small business, and DHi (Defense Holdings, Inc.) to develop a new electrical brush that could offer high reliability, longer life, and reduced wear debris having very low conductivity. The effort was successful and the new technology—a brush consisting of a bundle of thousands of very thin, flexible metal fibers (a “metal fiber brush”) running on their tips under very light spring pressure—is now being commercialized. What was originally developed for submarines is currently in use or under test in aircraft, power generation, shaft grounding, and other current transfer applications where clean, long-life power, and data transfer is important.

The patented tip-contact metal fiber brushes (MFBs, Figure 1) made by HiPerCon are much different from traditional monolithic carbon, silver-graphitic types of metal fiber brushes where the fibers make tangential contact. As might be imagined from the name, tip-contact MFBs run on their fiber tips.

Each brush contains thousands of hair-fine (50 micron) metal fibers that can flex so they stay in contact with the sliding surface (Figure 2“>). Since each fiber tip is in contact with the sliding surface there are literally thousands of contact points per brush, as opposed to monolithic carbon brushes where there might be between six and 12 contact spots at any given time. Since the carbon brush only makes contact at a few places, the brush is exposed to localized heating and higher wear at those locations. As these contact spots wear off the current is transferred to other contact spots, and then still others. This shifting of contact spots creates a significant amount of electrical noise and conductive wear debris. The hardness of carbon brushes also makes them susceptible to chattering and vibrations, which adds to the signal noise. Traditional carbon brushes don’t work well in a variety of conditions including very low or very high humidity, high runout where there are long periods of low or no current operation, or where they are required to sit for long periods of time with no current and no rotation. Tip-contact MFBs also avoid these problems.

Tip-contact MFBs can be made from copper, silver, gold, or other metals. The material selected for the fibers is based on sliding surface material, environmental conditions, and performance requirements. The fibers can be conditioned for extreme conditions such as <10 percent relative humidity or to inhibit oxidation of the sliding surface. Once conditioned by this patented process the fibers never need retreatment, eliminating the need to reapply brush lubricant during maintenance.

The specially-processed fibers in a tip-contact MFB are formed into a loosely-packed bundle. A brush is typically 1/6 fibers and 5/6 open space between the fibers. Since each fiber is in contact with the sliding surface and each fiber flexes with the sliding surface imperfections, very light spring forces can be used on the brushes. The fibers used in tip-contact MFBs do gradually wear, but because the spring pressure is so low that wear occurs very slowly. Typical MFB spring pressures are 20 percent of an equivalently sized carbon brush. Testing has shown that the wear particles produced resemble a microscopic curved oak leaf, and while the fibers themselves are highly conductive, tip-contact MFB wear debris is not particularly conductive unless the particles are compressed together tightly. As a result of all of these factors, tip-contact MFBs produce far less wear debris than competing carbon brushes, and the largely non-conductive debris causes far fewer problems and is easier to collect and remove.

With tip-contact MFBs, an outer wrap (Figure 3) retains the shape of the brush and can be made in nearly any shape or form factor. This outer wrap wears at the same rate as the internal fibers and can be made electrically conductive or insulating depending on the application. The stiffness and thickness of the wrap can be increased to handle severe vibration and runout conditions of up to 60 mils at sliding speeds of 20 meters/second.

Advantages of Tip-Contact MFBs
Service life: Since the fibers run on their tips (Figure 4) almost the complete fiber length is available for brush service, so in many cases brushes can be made longer if a longer service life is desired. Also, the very low spring pressures result in very low friction and correspondingly low brush and slip ring wear rates. Below are actual service life examples of HiPerCon’s tip-contact MFBs:

• A brush with 0.4” of fiber wear running on a coin silver 3” diameter slip ring will last 300M revolutions;
• A brush with 0.78” of fiber wear operating on a 3.5” diameter slip ring will last 400M revolutions;
• A brush with 1” of fiber wear running on a gold-plated 12” diameter slip ring will last 1.24B (1.24E9) revolutions;
• A brush with 2” of fiber wear operating as a grounding or potential energy brush running on a 1” carbon steel shaft will last 13.5B (1.35E10) revolutions.

Wear debris: Long brush service life reduces maintenance requirements only if the equipment using the brushes does not experience grounds as a result of brush wear debris from these longer-life brushes. It is counterproductive to develop a brush that can last forever if it produces so much conductive debris that maintenance personnel must frequently open, inspect, and clean the equipment to prevent grounds and shorts. Anyone who has ever worked on a carbon brushed slip ring assembly knows the burden of cleaning carbon brush debris. Figure 5 demonstrates the results of a comparison of the wear debris after 10M revolutions between a single silver-graphite brush on the left and a single HiPerCon tip-contact MFB on the right.

Electrical performance: HiPerCon’s MFB’s baseline capacity is 250 amps/inch2 of brush surface area, with 1000 amps/ inch2 possible under certain conditions. These high current capacities are achievable because there are thousands of contact spots in each brush and each contact spot has its own parallel current path through the brush. In fact, the limiting factor in the brush is generally not the brush itself, but rather the brush shunt. The data transfer capacity is also aided by these multiple contact spots. Instead of only a dozen contact spots, a HiPerCon tip-contact MFB measuring .25” X .25” has approximately 4,000 contact spots. This results in very low contact drop and very low noise. HiPerCon’s MFB’s typically exhibit an order of magnitude lower contact drop and noise compared to silver graphitic brushes.

Environmental performance: It would be nice if all carbon brushes could operate under pristine laboratory conditions, but the real world requires brushes to operate in less than ideal environments. Anyone who has replaced carbon brushes operating in an oily or hydrocarbon-filled environment will attest to the mess carbon brushes create. The oil breaks down the binder material used in monolithic carbon brushes, turning the once-solid and hard brush into a soft tar-like mess. MFBs are impervious to oily environments, and they don’t break down. Other atmosphere containments that destroy carbon brush films such as silicones and sodium chloride do not affect MFB operation.

Applications: Since tip-contact MFBs can be shaped like carbon brushes, they can be easily retrofitted to most carbon brush applications by simply reducing the spring force. HiPerCon MFBs have been retrofitted to replace carbon brushes in field excitation slip rings in Navy submarine motor-generators and for power and data transfer slip ring systems. Retrofit brushes have been designed for—but not yet deployed in—Army Black Hawk helicopter main rotor de-icing systems, E-2C & C-130 aircraft propeller de-icing systems, and hydro-electric generator excitation systems.

Wind Specifics
With its exclusive value-added reseller DHi, HiPerCon is presently introducing tip-contact MFBs for two applications of interest to the wind system community. These are: 1) brushes for wind turbine blade pitch control slip ring systems and; (2) shaft grounding brushes.

Blade pitch control slip rings: HiPerCon-DHi is offering blade pitch control slip ring systems with brushes designed to last 20 years. Since HiPerCon’s metal fiber brushes deposit so little wear debris and require no periodic lubrication, the slip ring service interval can be extended to five years and simply requires inspection and cleaning.

Grounding brush: This shaft grounding device (Figure 6) is a cost-effective means of preventing bearing damage as a result of stray shaft currents induced in shafts. This problem is particularly acute in variable frequency drive (VFD) motors. HiPerCon’s patented MFB technology allows it to offer a grounding brush system that can withstand severe operational environments with a very long life:

• Operates in oil-soaked environments;
• Service life in excess of 20 years or 1.8M miles of sliding distance at shaft speeds up to 20 meters/sec;
• Total system resistance when operating on an unconditioned bare steel shaft is ~3.7mΩ;
• One brush is capable of carrying 40 amps continuous current;
• Very small footprint and can be easily adapted to any motor or shaft with standard mounting options;
• Uses silver alloy fibers which are much less expensive than competitors’ gold fibers and can run directly on a steel shaft without shaft modification;
• Can easily be replaced during operation.

No shaft grounding system lasts forever, since any shaft grounding device must make contact with the rotating shaft to conduct current. The contact of two metals in relative motion always results in friction, and friction results in wear. These brushes, however, do have a long service life because they incorporate the very low wear rates of a light spring pressure metal fiber brush with very long fibers.