September 2012

Many 3D cutting jobs worldwide are done through HGG machinery. Founded in 1984, HGG Group is the world’s only company fully devoted to steel profile cutting, providing both tailor made machinery and knowledge to the highest standards. Their machines are sold worldwide to leading companies in the offshore, steel construction, process piping, shipbuilding and other industries. Figure 1

HGG profiling machines provide quality cutting according to the latest ISO standards, (ISO 9013) which enable easy operating, programming, industry specific customization, and durability. HGG manufactures bevel cutting machines that are particularly suited for processing large components. “We like challenges,” says Peter Tool, R&D manager at HGG. “Our greatest strength is that we design our systems and software from the bottom up – so we retain flexibility. Short channels of communication allow us to come up with completely new processes in very little time.”

Measuring Technique: The Key to Success
A German manufacturer of wind turbine components, EEW located in Erndtebrück Germany, placed an order with HGG. EEW wished to manufacture foundation structures, known as tripods, for an offshore wind farm using high quality steel. The task was to produce cylindrical members cut precisely in 3D from 400-ton, 60-meter long, 6-meter high steel tubes. HGG realized from this basic information that adopting the correct measuring technique would be key to the success of the project.

A tube weighing 400 tons deforms under its own weight when placed on the cutting machine. This deformation changes the diameter of a tube by up to 20 millimeters and leads to undesirable drifts. However, the changes in diameter are not constant; when the tube rotates on the cutting machine – the ovality changes with the movement of the tube. In addition, a 60-meter long tube sags several centimeters at mid-span between supports. The structural frame of the cutting machine itself also deforms while supporting this extremely heavy load. In the face of deformations like these, even the most accurate machines are incapable of delivering a clean cut. With tubes costing around 100,000 € (approximately $122,000USD) each, cutting errors cannot be allowed to happen. Therefore Tool and his team decided to integrate a measuring system into the cutting machine.

No Expensive Scrap
To address this challenge, the users needed to know the position of the tube relative to the cutting machine at all times. If the exact coordinates and deformation of the tube on the machine are always known, it is possible to continuously compensate for the movement of the cutting head thereby eliminating expensive scrap. Figure 2

Peter Tool quickly found a suitable method of control. He had become aware of the potential of laser trackers at an earlier trade show and recognized that there was no alternative to the range capability of laser metrology for the dimensions of the parts in the EEW project. HGG decided to couple the Leica AT901 Absolute Tracker to the cutting machine to ensure the necessary accuracy and adequate measuring range for the 60-meter long tubes. Their requirement necessitated the positioning of the measuring instrument in front of the tube. The typical measurement volume of the tracker can extend to 160 meters and no other laser tracker could offer the desired accuracy over the large distances.
 
Laser Tracker Monitors Cutting Head and Component
From the start, the company had one objective: the machine had to be capable of being properly operated by a single person. Therefore HGG fully integrated the laser tracker into the cutting machine so the operator does not even have to know how to use it. The instrument tracks several reflectors on the cutting head and on the tube. Every section of the tube is fitted with a reflector, which lets the cutting machine operator know how much the tube bends. The laser tracker supplies the coordinates of one point every 100 milliseconds. These coordinates are then fed back to the cutting machine software, which has also been configured to control the tracker – a task made possible by the programming interface of the system. Figure 3

HGG installed the new cutting machine in the EEW production facility in Rostock, Germany.  Mounted on an 8-meter high platform, tracker monitors the movement of the cutting machine and the supported tube. This measuring system has to work in a very difficult environment. Components of these extreme dimensions and weights frequently give rise to vibrations. The tracker dealt with these issues without any problems and the dust created from the cutting operations did not adversely affect measurements. As Tool mentions, “Even with several millimeters of dust in the reflectors, they always continued to work perfectly.” Leica Absolute Tracker

Perfect for Wind Farm Infrastructure Dimensions
HGG developed a new type of bevel cutting system, which integrated the laser tracker to continuously monitor the cutting process. Using the measured data in the metrology-aided cutting system, the machine cuts the 60-meter long, 400-ton tubes into individual sections with an accuracy of 0.5 millimeters. Peter Tool is proud of this development, “Thanks to the Leica Absolute Tracker, the HGG machine is capable of cutting extremely large components such as those now in common use by wind turbine manufacturers. Our customer successfully performed this task with precision and reliability.” 

The world has seen a significant expansion of renewable energy generation over the last decade. Wind energy has become the greatest contributor to this growth. The wind turbine generated energy depends on the wind potential and the turbine availability impacted by faults and repairs. Faults are responsible for reduction of the overall capacity of wind turbines. Supervisory control and data acquisition (SCADA) systems record wind turbine parameters, which can be used to monitor their performance. Successful applications of SCADA data usage include: power optimization [1], power curve monitoring [2], and fault diagnostics and prognostics [3].

Data envelopment analysis (DEA) is an analytical technique to assess capacity factor of wind turbines. DEA has been successfully applied in healthcare, marketing, and manufacturing. However, the application of DEA in wind energy is new. Assessment of turbine capacity in presence of faults is performed using SCADA data and fault logs. The results of this analysis are useful in prioritizing maintenance operations.

Turbine Capacity and Data Envelopment Analysis
The capacity of a wind turbine can be measured by its power producing capability in a given operational time period. Of two turbines operating for a certain fixed time, a turbine producing more power is considered to be more efficient. Apart from the wind speed, downtime caused by turbine faults and power curtailment leads to power generation losses. In simple terms, the capacity factor of a wind turbine is expressed as the ratio of actual power generated by a wind turbine over the maximum power that could be produced. The capacity of a wind turbine can be affected by factors such as repair and maintenance downtime and external downtime (power curtailment), and fault downtime. Analysis of the impact of the faults on the capacity of wind turbines is imperative.
 
Data Envelopment Analysis Single Input-Single Output
Data envelopment analysis is a powerful technique for the assessment of relative capacity of wind turbines [4]. The analysis presented in this article is based on data (Jan 2006 – Dec 2008) from 10 wind turbines, each 1.5 MW. The cut-in, cut-out, and the rated wind speed were 3.5m/s, 25 m/s, and 12 m/s, whereas, the rotor speed ranged from 0-23 rpm. Figure 1 illustrates the performance of wind turbines by DEA. Clearly, turbine 1, turbine 5, and turbine 8 are efficient and thus makes the capacity frontier, whereas, turbine 4, turbine 6, and turbine 10 are inefficient. DEA assesses relative capacity of wind turbines. Turbines with relative capacity score of 1 are considered to be efficient, whereas turbines with relative capacity less than 1 are inefficient.

Multiple Input-Single Output
To gain more insights into turbine performance, operational time, maintenance and repair downtime, external downtime (power curtailment), and fault downtime are considered. An input oriented data envelopment analysis approach is used to assess the turbine capacity under different downtime scenarios. Figure 2a, Figure 2b, Figure 2c, Figure 2d illustrate the capacity of 10 wind turbines for different downtime scenarios. The results provided in Figure 2 (a)-(d) are summarized in Table 1. Based on the analysis, the capacity degradation is higher in scenarios considering fault downtime (Figure 2c), and external downtime (Figure 2d). Turbine 8 found to be the efficient in all scenarios. While the downtime due to scheduled repair and maintenance, and power curtailment cannot be avoided, analyzing the fault information is useful in improving capacity factors of wind turbines.

Even though the turbines analyzed here are from the same original equipment manufacturer (OEM), certain replacement components such as generators, brush type, and bearings might possess different characteristics.Figure 3b – Figure 3a For example, the ABB generators installed in certain wind turbines may have poorer performance (due to overheating issues) than the Hitachi generators. Thus, the inefficient turbines identified here can be made efficient by closely following the components of efficient turbines.
 
Multiple Input-Single Output With Fault Information
A typical wind turbine issues many status codes. Wind turbines statuses can be a system update only (turbine curtailment, turbine idling) or fault informative (blade pitch fault, generator fault). The fault informative statuses triggering more than the specified limit may cause the turbine to shut down or run sub-optimally, resulting in poor capacity factor. Figure 4 represents such fault informative statuses observed from 10 different wind turbines over a period of three years. Table 1

The Figure 5 graph presents the turbine capacity under different fault scenarios. The analysis is done on the data combined from 10 wind turbines. Based on the results, turbines without any statues is the ideal condition, however, while just fixing the critical statuses (as mentioned in Figure 4); the efficiency can be improved to a greater extent. Among faults, fixing the blade pitch faults and timely performing the battery test can improve the turbine capacity. Generators, gearbox related faults do not differ much from the original (real) capacity due to their less frequent observations in the data. While the relative capacity score under different fault scenario does not seem to be differing, it has bigger implications in terms of overall production loss (Figure 6). Based on the historical data, turbines on average produce 39000 KWh of energy per month. Thus, in one year, by fixing certain faults, the overall yield can be improved.
 
Conclusions
The downtime related with power curtailment and faults are the main factors responsible for turbine inefficiency. The analysis performed here clearly indicates the role of data envelopment analysis approach in wind turbine capacity evaluation. The approach is particularly useful in prioritizing maintenance tasks. In the event of several concurrent faults in a wind farm, faults causing the most degradation in turbine capacity should be fixed first.  

Hurricane season officially began June 1, but activity started early this year with four named storms appearing before July 1, making 2012 the only year on record that this many storms developed so early in the season. This continues the enhanced storm activity that we saw in 2011, which produced 19 named storms compared with a typical year’s 11. This total tied the record for the third highest number of named storms in a single year.

While traditional hurricane season forecasts attempt to estimate the number of named storms that will form during the year, of greater interest is how many of these storms will impact the U.S. and its business operations. On average, the U.S. experiences 1.78 hurricane landfalls per year. The most likely number for annual hurricane landfalls is one, which occurred 30 percent of the time between the start of hurricane records in 1861 until 2011. In recent years, hurricane landfalls have been much less frequent, with only one U.S. strike in the past three seasons (Hurricane Earl landed on the Eastern Seaboard last year).

It’s important to avoid complacency, however from this recent quiet landfall trend: The challenge for the wind power industry – especially operations in the Gulf Coast states – is to stay alert and be aware of the nuances in this year’s climate conditions and how these patterns and storms could affect operations.

The Big Picture
Each hurricane season depends on two ocean temperature cycles, one short-term and one long-term. The long-term Atlantic multi-decadal oscillation (AMO) cycle is, as the name suggests, a time of either warmer or colder water in the Atlantic Ocean that can last for several decades. We are currently in the warm phase, which typically leads to an increased frequency of hurricane development in the Atlantic Ocean (while the cooler water phase inhibits them). The short-term, more annual cycle is the better known as El Niño/La Niña climate patterns in the Pacific Ocean, which can influence storm numbers from year to year.

The El Niño/La Niña patterns can vary from year to year and refer to deviations in the surface temperature of the tropical eastern part of the Pacific: warmer surface temperatures are known as El Niño (“little boy” in Spanish), named after the Christ child because the effects of the pattern are often felt around Christmastime in South America. The opposite, cooler temperature pattern is dubbed La Niña (“little girl”). The more extreme the El Niño or La Niña is, the more extreme the weather can become in many regions, bringing about floods, droughts and storms.

Climate scientists and weather forecasters recognize the formation of an El Niño climate pattern when the surface pressure over the Indian Ocean and South Pacific begins to rise, accompanied by a fall in air pressure over the central and eastern Pacific. The sustained warming of the central and eastern region often brings heavy rainfall with it, while the western Pacific is steeped in drought.

An El Niño also brings about increased wind shear (differences in wind speed or direction over a short distance in the atmosphere) downstream into the Atlantic region. Increased wind shear creates unfavorable conditions for storms to form or intensify in the Atlantic basin because there are stronger winds aloft in the tropical regions. In general, the El Niño effect tends to inhibit tropical storms from developing in the Atlantic (or if they do develop, they are more likely to remain less intense or of fewer numbers), while La Niña conditions are more favorable for the formation of storms. Studies have shown that there are many more storms on average during La Niña years, and fewer during El Niño seasons.

We are currently in a developing El Niño phase, although a weak one. We are predicting these conditions continuing through the fall and impacting hurricane development by making it a relatively quieter end to the year in terms of total numbers of storms that form in the Atlantic during the more active September/October part of the season. Conversely, the warmer waters we have been seeing in the Gulf of Mexico and off the southeastern coast of the U.S. this year are more likely to feed any storms that do develop and may help them reach hurricane intensity more quickly as they approach the mainland.

The bottom line: We are predicting an average or below-average year for the number of tropical storms and hurricanes that form, especially the latter half of the season due to El Niño, but those storms that do develop and head into the Gulf of Mexico and the southeastern U.S. could become more intense due to the warmer waters near the U.S. this year.

The Good News: The Atlantic Coast
As mentioned above, El Niño’s increased wind shear creates less favorable conditions for storms to form in the Atlantic basin. In addition, this year there is a large patchwork of cooler than normal sea surface temperatures in the central and eastern Atlantic area, where many late-season storms develop. This colder water may also help to reduce the number of the longer-tracked hurricanes that develop off the west coast of Africa and track westward. These storms can become stronger hurricanes as they travel for a long time over the open waters of the Atlantic. Many of these storms tend to curve north as they approach the East Coast of the U.S., so reducing the number and probable intensity of these storms is a step in the right direction. The exact track of any individual storm however is dependent on the steering winds in place at the time of each storm, so land falls or lack of them anywhere cannot be foreseen more than a few days in advance.

These conditions lead us to forecast a near-average or below-normal number of tropical storms in the Atlantic region this season. This is good news for the relatively few wind farms up and down the coast: Although operators should always have a plan in place, we believe there is a reduced risk compared to average for an interruption because of tropical storms or hurricanes.

Where to Be Watchful: The Gulf Region
While the wind shear conditions generated by El Niño lower the likelihood of storms and hurricanes, we have also been watching the warmer sea surface temperatures in the Gulf of Mexico that have existed since the spring. This warmer water could contribute to more hurricane development closer to the U.S. mainland. In addition, we don’t have the strong area of high pressure that we saw last year in the Gulf, which helped steer away hurricanes (and which also caused the unprecedented drought conditions).

These factors have led us to forecast an average or slightly above-average risk of tropical storms in the Texas coast and Gulf region for the remainder of the season.

But the simple number of storms isn’t the whole story: The warmer waters in the Gulf also create more favorable conditions for storms to intensify quickly as they near the U.S. We are concerned that storms could strengthen rapidly as they approach the continent, giving us a shorter lead-time to secure business operations and evacuate the area. Figure 1

This is one of the most important details to be aware of if you are in the wind power industry: conditions that encourage storms to intensify quickly mean shorter notice of destructive storms. Storm intensity is generally volatile and difficult to predict, and the warmer Gulf waters may make that even more challenging. This year, do not assume a multiple-day lead-time on hurricane development: Ensure crews and available equipment are ready to move on short notice.

What This Means for the Wind Industry
While we don’t believe this will be a gangbuster year for tropical storm total numbers, any wind power operation in the Gulf of Mexico region should be aware that current and forecasted conditions can facilitate more storm development in the area and contribute to a storm swiftly intensifying. Rather than a week’s notice, operators may only have a few days, so monitoring storm conditions closely will help ensure crews are kept safe and damage to movable equipment is minimized.
 
Typical threats to a wind farm from hurricane landfall include strong winds, storms and flooding: An average hurricane is about 300 miles wide with outer rain bands made up of dense thunderstorms. Damaging winds are generally confined to within 100 miles of the coastline, but tornadoes from the outer bands of a hurricane can reach as far inland as several hundred miles and are a risk for several days after the storm makes landfall. The stronger the hurricane, the more likely that tornadoes will result. Flooding rains can travel even further inland – even as far inland as the Midwest – where wind farms are more prevalent.

Tools for Mitigating Risk
While good wind farm operators always keep an eye on the weather, there are a few tools that can help increase an operator’s understanding of conditions, how they will affect operations and when action needs to be taken to prepare for damaging weather and evacuate crews.

A comprehensive weather forecasting and detection solution should provide fast, accurate information with features specific to the wind industry, including wind speeds and lightning detection. Telvent’s MxVision WeatherSentry Online® provides this level of service, including location-specific information, precipitation forecasts that have earned awards for accuracy and the best lightning-alerting technology on the market.

MxVision WeatherSentry Online allows wind farm operators to easily assess risk with a display of all active hurricanes and tropical storms around the world. Users can also select individual storms for viewing, along with the ability to view multiple forecasts along with the official track for any tropical storm or hurricane across the globe.

Because field workers typically do not have access to a computer, communicating via cell phone is critical. Telvent’s MxVision WeatherSentry Online solution and its mobile application can provide detailed weather information about a wind farm maintenance crew’s specific location based on a cell phone’s GPS signal. This is especially helpful to the wind industry, which often has crews moving across vast areas that would typically require them to enter new GPS coordinates into the weather detection system every time their location changed. Instead, a crew’s location is automatically updated, the forecasts are adjusted accordingly, and alerts will sound on a crewmember’s phone when severe weather moves into a predefined area (30 miles out, for example). Specific thresholds can be set for conditions like wind speed and lightning, providing crews with a customized detection system and alerts for their geographic area. This efficient solution gives them enough time to exit the area safely and seek shelter.

Lightning can be a major concern during tropical storms, especially for wind farm maintenance crews working on turbines. Telvent’s tool is the only one in the industry to offer future lightning forecasts, which allows users to better visualize where lightning may strike in the next hour through a color-coded map, demonstrating the probability of lightning strikes.  Future lightning allows wind farm operators to plan appropriately for crew safety.

Telvent’s tool provides detailed, hourly forecasts three days out, making it particularly useful if hurricanes are approaching and crews need to be aware of high wind speeds that put maintenance activities at risk, or potential lightning strikes from subsequent thunderstorms. While operators will be aware of a hurricane’s landfall several days out, the erratic nature of the resulting weather can affect operations for several days. Close monitoring of weather conditions and readiness to change course quickly will ensure that no one is caught off guard.

The Forecast: Keep An Eye Out in the Gulf
The good news is that we expect an average or quieter-than-average fall season for total tropical storm and hurricane activity in the Atlantic basin. In the event that storms do develop, there is a greater chance however that they will be located near the U.S. – especially the Gulf region – and gain strength more quickly than expected. Wind farm operators who have the right tools and an emergency plan that can be executed on very short notice will be able to weather any storm as best and as safely as possible. 

Silent behemoths supporting 60-meter blades that rotate at up to 300 km/h, industrial wind turbines are modern engineering miracles. These sentinels of electric power stand up to 152 meters tall and must withstand decades of harsh environmental conditions found offshore, in coastal regions and on mountaintops.

Industrial wind turbines cost roughly $1.2 to $2.6 million to build, and installation costs increase the average investment to approximately $3.5 million per turbine. Turbine manufacturers and owners are constantly looking for ways to reduce manufacturing and maintenance costs and increase profitability by shortening production cycles, increasing production volume, and simplifying maintenance requirements.

Adhesives, sealants, lubricants and surface treatments play critical roles in the life, health and financial soundness of wind turbines. These materials are used during every phase of manufacturing, installation and day-to-day operation.

Turbine Manufacturing and Assembly
For blade and nacelle production, gigantic molds are first treated with semi-permanent mold release agents that allow large-scale composite parts to be easily removed from the mold. Blade halves and nacelle body components are bonded together and sealed using structural adhesives such as two-part polyurethanes that prevent crack propagation, micro-cracking and fatigue, and ensure the long-term integrity of the structure. Two-part polyurethanes also fill voids found on the molded assemblies.

Two component polyurethane adhesives and MS polymer sealants are used to permanently bond components such as access doors, rain deflectors and gurney flaps to the blades. Color-matching, weather-resistant MS polymers and high performance sealants protect and seal the blade and nacelle interior and exterior from moisture and environmental contaminants.

When metal tower components are manufactured, surface treatments such as coatings, conversion coatings and cleaners/degreasers prepare the surface to improve corrosion resistance and paint adhesion. These large parts are then ready for assembly.

On the tower, sealants prevent moisture from penetrating in through tower section breaks and prevent corrosion on load support plates, platforms, bolt heads, ladder frames and other metal surfaces. Anaerobic threadlockers lock and seal large threaded fasteners. Structural adhesives are used to bond and secure ladders and other components.

Anaerobic adhesives play critical roles throughout the turbine assembly, locking and sealing threaded fasteners found on the base, tower, nacelle and blades. Anaerobic materials are widely used in hub, bearing and the gearbox assembly where they retain pitch and yaw bearings, and seal gearboxes, flanges and hydraulic fittings. Anti-seize lubricants protect power train splines, mounting bolts, and exposed fasteners.

Throughout the turbine, heavy duty solvent-based and aqueous cleaners remove dirt and residues from composite and metal parts and prepare them for installation and operation in the field.

During installation, epoxy grout materials are used to create a level, secure base for tower assembly. High strength epoxy grouts bond to steel, concrete and other construction materials and withstand high torque loads.  Urethane sealants bond, seal and waterproof tower bases.  Cables that route out of the turbine to deliver electricity must be sealed to stop moisture/water from entering the turbine, preventing corrosion. Highly flexible silane modified polymers demonstrate good adhesion to many substrates and create a soft, elastic seal. Figure 1

Turbine Maintenance
From the moment a turbine is assembled and begins to turn, it is exposed to environmental hazards. Lightning, turbulence, sand, rain, hail, snow and bird-strikes all contribute to wear and damage to the blades and nacelle.  Corrosion affects the aesthetics and eventually compromises the strength of the tower, while erosion damages the concrete foundation, causing cracks, chips and spalling.

Composite blade tips commonly experience micro-cracking and structural cracking that can be significant and require installation of a new tip or a structural patch. Bird and lightning strikes can penetrate the blade and require repair to the core material, the blade substrate and the blade surface. Pitting and wear caused by weather and environmental elements can decrease the aerodynamics and efficiency of the wind turbine.

High viscosity, structural polyurethane putties are hand applied to the eroded edges of the blade. Fast-curing, abrasion-resistant putties fill large gaps and holes caused by lightning or bird strikes. Cartridge dispensed two component polyurethane adhesives patch damaged tips and fixture in just 75 minutes. To reduce the chance of subsequent lightning strikes, lightening diverter strips designed to transmit and ground lightning away from the blades, can be applied to blade surfaces using a structural adhesive. Working together, these adhesives and sealants return the blades to their original smooth and wind resistant design and allow the blades to rotate again with little downtime.

On and in the nacelle, sealants are used to protect the generator and motor housing, panels, hinges, service doors, man-holes and exterior appliances such as wind indicators, lights, rails or cable breakthroughs from moisture ingress and corrosion. Anaerobic materials protect yaw bearings and keep gearboxes operating efficiently and reliably. Anti-slip coatings create walking surfaces with good traction so that maintenance workers will not slip in cold, wet and icy conditions outside the nacelle or slippery, lubricant and coolant-coated surfaces inside the nacelle.

The tower assembly must be treated on an ongoing basis with maintenance chemicals to keep it strong and solid throughout the long life of the turbine. High flexibility adhesives and sealants ensure the tower sections stay together and seal out water and chemicals that can cause corrosion and enter the tower assembly. Chemically resistant coatings and galvanizing compounds protect the metal towers from corrosion and damage. Threadlocking and structural adhesives keep accessories such as ladders and platforms in place and prevent threaded fastener failure. Figure 2

To ensure that blades achieve maximum aerodynamic efficiency, they must be regularly cleaned of contaminations such as algae, dirt and sand.  Water-based cleaners quickly cut through grime and reduce the effort and time required for cleaning.  By applying specially formulated coatings, maintenance crews can reduce the likelihood of new contaminants sticking to the blades and can increase the turbine’s total power production until the next scheduled cleaning.

On the base of the turbine, damage and cracks in concrete pads will deteriorate over time from exposure to outside elements. Repairing damaged areas using crack fillers and fast-fixturing concrete repair products increases the life of the concrete structure and helps it resist future damage.

By incorporating adhesives, sealants and surface coatings from start to finish in wind turbine production, manufacturers can produce more robust turbine components and longer-lasting assemblies. Automated processes shorten production cycles, increase production volume and reduce manufacturing costs.  And stronger, more reliable turbine components mean less maintenance when the turbine is assembled and in operation in the field.

During installation and maintenance, wind farms that use adhesives, sealants, lubricants, surface treatments and cleaners top to bottom on their turbines simplify and speed installation, minimize downtime and ensure a safer work environment for crews.  The turbines are more efficient structures that operate more reliably and provide greater energy output over the expected lifespan, therefore the wind farm is more profitable and less manpower and money is dedicated to maintenance issues.