Reach for the skies

Currently 2 megawatt (MW) wind turbines on 80 to 100 metre towers are a standard size throughout the wind turbine market for onshore wind farms but this is changing. Now 3 MW turbines, on towers up to 150 m tall, which are more commonly erected offshore, are being installed at onshore wind farms across Europe.

At the time of writing in March 2013, reports from the European Wind Energy Association (EWEA) say that, “The EU wind energy sector installed 11.6 GW of capacity in 2012, bringing the total wind power capacity to 105.6 GW. Wind energy represented 26% of all new EU power capacity installed in 2012, and investments of between €12.8 billion and €17.2 billion. It is now meeting 7% of Europe’s electricity demand – up from 6.3% at end 2011.”

Although most EU member states are meeting or exceeding their country’s individual targets for wind energy, 18 member states are falling behind. These countries include Slovakia, Greece, Czech Republic, Hungary, Portugal and France.

With countries around the world striving to meet their wind capacity production targets, contractors in Europe and the USA are experiencing both a demand for larger wind turbines and an increase in the number of wind turbines being erected.

BMS Heavy Cranes (BMS HC), a contractor for onshore and offshore wind turbine projects, is already witnessing the move to larger turbines, “We are currently erecting 26 x SWP 2-3 DD wind turbines on 115 metre shell towers near Stamåsen in Sweden. At another project site we are busy setting up an onshore wind farm near Vetlanda in Sweden called Lemnhult. We started in September 2012 and have been setting up 32 x V112 3 MW turbines on 129 metre steel towers.”

Further south, in the Dutch town of Eemshaven, Netherlands, are some even larger wind turbines. A wind turbine with a machinery housing in the 6 MW class has been installed on a tower at a height of 110 m using a 1,350 tonne capacity Liebherr LR 11350-P1800 lattice crawler crane with the manufacturer’s new parallel Power Boom. The housing weighed 340 tonnes. Plans are in place for 48 turbines of this type to also be installed from 2013 onwards in the North Sea East offshore wind park, off the island of Heligoland, crane manufacturer Liebherr adds.

Nordic Crane, a provider of mobile crane and specialized transport, which operates solely in Scandinavia, is also seeing this emerging trend. One of its ongoing onshore projects in Jädraås, Sweden, has included the erection of 66 Vestas 3 MW turbines on 119 m towers.

This trend for high numbers of turbines is not expected to last forever, as a company spokesperson from international heavy lifting and transport engineering company Sarens, explains, “The trend for the coming years seems to be that for Western-Europe there are going to be fewer of the big parks that have more than 20 turbines. Instead there will be smaller parks, with 1 to 5 relatively large turbines.”

Outside Europe, the height of wind turbines has also increased in the USA. This has proved to be a challenge for contractors. In Eastbrook, Maine, construction contractor, Reed & Reed is installing 19 wind turbines at the Bull Hill wind farm. Ron Babb, a crane operator with the Woolwich, Maine-based company says, “This job was a real challenge for us because we moved from 262 feet (80 m) towers up to 312 feet (95 m) towers.” A Boom Raising System from Manitowoc was eventually used so the company could complete the onshore wind turbine installation project.

Safe heights
As the height of wind turbines, whether onshore or offshore, increases, safety legislation and guidelines become ever more stringent. At the time of writing, all mobile cranes working in the European market must fulfil the requirements of the European Machinery Directive 2006/42/EC. The relevant European standard for mobile cranes is EN 13000 and the regulation includes load assumptions for calculating the load bearing structure of a mobile crane.

Even when safety standards have been met, however, wind turbine installation projects can still present a danger. As explained in the FEM (the European Association of Lifting Equipment Manufacturers, Product Group Cranes and Lifting Equipment, Mobile Cranes) Guideline Safety Issues in Wind Turbine Installation and Transportation, “lifting loads in strong wind conditions can present a potential danger that should not be underestimated... When lifting loads with a large surface area exposed to wind such as rotor blades or complete rotor units of wind mills, the conditions and assumptions for calculation of wind loads may differ significantly from the standard values provided by EN 13000.” As the industry has witnessed, when loads are affected by wind forces during lifting operations, serious accidents can, and do, happen.

Preventing injuries of any kind is crucial for contractors and manufacturers alike. Unfortunately, due to a growing amount of pressure on contractors regarding time constraints, there is a general concern that “corners will be cut” to meet tight deadlines. As the FEM Guideline states, in some cases lead time is often reduced to an unacceptable level, which can jeopardise worker safety.

To avoid injuries of any kind, contractors are implementing safety procedures into their project policies. BMS HC, for example, includes a “zero risk policy” into project schedules. A company spokesperson explains, “We work according to the HSEQ (Health, Safety, Quality and Environment) principle and have high standards for these. This includes documentation with lift studies, risk assessments, on site frequent meetings and an assigned project manager for each separate project.”

For crane manufacturer Sarens, lifting studies are drawn up for every wind turbine project, identifying effective wind sail areas of all wind turbine components to be lifted.

Calculating wind speeds
What contractors must be aware of is that the permitted wind speeds in the crane’s capacity charts are often not valid when lifting rotor blades, rotor assemblies or other structures with big sail areas. As stated in the FEM Guideline, “lifting of these items will require lower wind speeds, compared to the wind speeds allowed when lifting tower sections, a nacelle or other heavy items.”

Crane and transport rental company Dufour Cranes, devises safety plans prior to lifting projects to accommodate this element. Its safety plans inform customers on wind speed limits based on manufacturer recommendations. The company also carries out inspections and periodical checks to ensure the safety of its equipment. “For the lifting equipment and cranes, this inspection is performed every six months in France (by external party) and every three months in Belgium (by external party) at each assembly.” In addition, the company sates that no lifts are allowed in “gusting” conditions, a weather which is a weather condition of universal concern throughout the lifting industry.

In reference to “gusting” conditions, the FEM Guideline states that, “Regarding EN 13000 the wind speed referred to in capacity charts is the so called ‘3-second gust’ measured at the highest point of the boom system, and not the average wind speed measured at a 10 metre elevation over a time period of 10 minutes as given by most weather stations. The 3 second gust wind speed can easily be higher by a factor of two and more; i.e. taking into account the average wind speed at 10 m elevation may significantly underestimate the real conditions.”

The three factors to take into account here are wind surface area of the rotor and rotor assemblies; drag factor; and “3 second gust” wind speed, which is measured at the highest point of the boom system. “These factors are among the reasons why thorough planning is required, the weather conditions need to be observed and why waiting time should be expected and calculated when planning the lifting of rotor blades and rotor assemblies,” the FEM Guideline states.

To meet these requirements, crane rental and transport company Felbermayr, Austria, uses Liebherr and Terex cranes for wind turbine projects. As a company spokesperson says, this is because “each of these cranes has a producer manual in which it is clearly stated under which conditions it is not allowed to lift.”

Nordic Crane has a similar policy, whereby they follow the tables provided from crane manufacturers regarding maximum wind speeds. “However, it is always up to the crane operator to stop lifting activities even below these figures if he or she cannot guarantee a safe lift,” a Nordic Crane spokesperson adds.

Reliable and versatile
With pressure on contractors to keep to tight schedules, deciding what cranes to use for a turbine project isn’t a simple choice for end users. Nordic Crane uses a Terex Demag CC 2800 for some of its wind turbine projects, “Their superlift is easy to handle and the crawler crane can move fully rigged on a hardstand,” a spokesperson explains, “But whenever the turbines are small enough we use a Liebherr LTM 1500. This ‘small’ 500 tonne crane is hydraulic and easy to move.”

BMS HC use three main cranes to set up wind turbines, “These are the Liebherr LG 1750, the Liebherr LR 1750 and finally the Liebherr LR 1600,” a company representative says. “For port-handling operations we primarily use our LR 1750s and LR 1600, whereas our LG 1750 cranes are typically allocated to be used for onshore projects. The LG 1750 has a very high load capacity and has a very small chassis of only 3 metres wide, allowing it to travel on the public road.

“The LR 1750 has about the same capacities as the LG 1750 but cannot drive on the public road. But it can drive short distances while carrying the heavy load. Finally, the LR 1600 is our ‘smallest’ crane. It has a smaller engine and can, therefore, lift up to 600 tonnes. Just like the LR 1750, it has to be moved on the back of a flatbed, but it also has the same advantage of the ability to drive while carrying a heavy load.”

To meet varying demands, the Dufour Group owns a large range of crane models, “Our fleet offers a lot of different setup matching with most of the turbines, so we can easily reply to customer needs,” a company spokesperson says. “The main production equipment includes a LG 1750, which has a load capacity of 750 tonnes at 7 metres, a TC 2800, which has a lifting capacity of 600 tonnes and has great flexibility, and an AC 700 [Terex] telescopic crane, which is fast to rig and has optimised transport weights for all configurations.”

New technologies
With varying time constraints and the increasing “standard” turbine size and height, new engineering technologies are appearing across the lifting industry. Manitowoc has introduced its Boom Raising System for the 400 tonne model 16000. Also with the Wind Attachment this crane was used on the Bull Farm project, mentioned previously, to prevent the need for an assist crane.

“The boom raising system allows end users to lift up to 351 feet [106 m] of wind attachment boom plus 25 feet [7.6 m] of extended upper boom point (EUBP),” crane company Manitowoc explains.

The boom attachment has been used by crane rental company Guay Crane, “When new wind farm projects came along that required the erection of 80 metre turbine towers, we purchased a Manitowoc wind attachment (WA). With the WA, we have erected more than 100 wind turbines in the last year on projects such as Massif du Sud and Lac Alfred, with more coming this year. The WA gave our 16000s a second life.”

Other crane manufacturers are also meeting demands for the increasing heights of wind turbine projects. Terex’s most recent example is the Superlift 3800, a 650 tonne capacity class lattice crawler crane, which replaces the Terex CC 2800-1. For more on this crane see IC November 2012, page 14.

In June 2012 Liebherr introduced a 750 tonne capacity telescopic wheeled mobile crane, the LTM 1750-9.1. It also introduced a new boom system for the lattice boom mobile crane LG 1750, the SL12D2FB. “With a new and even more powerful boom system, the LG 1750 is now in a position to erect the new large types of wind power systems at tower heights from 140 metres to 150 metres,” a Liebherr spokesperson says.

The Liebherr crane uses a three strong 12 m lattice sections with a width of 3.5 m. It has a lifting capacity of 141 t at a height under hook of 143 m and 97 tonnes at 160 m. The basic machine of the LG 1750 can also be driven on public roads. At Bauma the LR 11000, a 1,000 tonne capacity crawler crane, which will be suitable for wind power thanks to its quick set up and compact design, will also be presented.

Of course, as turbines get larger and taller, for many companies transport problems are going to become even more complex, especially when travelling to and from different wind turbine project sites. As a spokesperson from Nordic Crane explains, “Our main concern is that roads will not be wide enough, especially since the cranes are much wider than the trailers.” This concern is felt by most crane manufacturers and contractors throughout the industry; but with road regulations becoming ever more stringent, this issue looks set to become even more of a challenge.”

For more on transport issues on wind turbine projects, look out for the wind power transport feature in an upcoming issue of IC.

Dismantling wind turbines
As demand for larger and taller wind turbines increases, smaller wind turbines are ageing and need more maintenance before becoming obsolete and requiring dismantling.

At a site in northern Germany, the dismantling of some smaller wind turbines has already begun. A 300 tonne capacity Grove GMK6300L all terrain crane dismantled two Enercon wind turbines in a day. Dismantling was at the Simonsberg wind park near Husum in northern Germany. The crane was rigged with a 34 tonne capacity heavy lift jib.

The first part of the project was removing the rotor blades. This was completed in a single 24 tonne lift, from a height of 42 m and working at a radius of 14 m. The 5 tonne gearbox was also removed. The crane is owned and operated by Heider Kranverleih, from Heide in northern Germany.

Nordic Crane has also experienced several dismantling projects. Fortunately the turbines dismantled so far have been “in good shape if you look at lifting points”, a company spokesperson says. Although the turbines can be in good shape, however, access issues can arise during dismantling projects. As a spokesperson for Dufour Cranes explains, “Access requirement must be the same as it was for the first installation of the turbines. A security margin between 10 and 20% must be calculated.”

Guntram Jakobs, Terex Cranes product manager, explains another potential problem during dismantling, “In Europe for the smaller wind turbines there are issues with picking up something that could be ‘fixed’ – but you don’t know how fixed it could be.”

Although not directly involved in any dismantling projects of late, BMS Heavy Cranes sister company Krangården/BMS, has been carrying out service work on existing wind turbines with hydraulic mobile cranes.

Laramie Equipment Company, Detroit, Michigan has also been involved with wind turbine repair work at a wind turbine site in North Dakota. During the project the company erected 100 wind turbines and repaired three using a Manitowoc 16000 crawler.

Dismantling turbines can be an issue. A spokesperson from Sarens explains some of the issues faced with dismantling projects. “The main problem to overcome when dismantling existing wind turbines is that the empty hook goes up and the rope on the winch drum is spooled on with almost no tension. When the load gets in the hook, there is a risk of snagging of the tensioned hoist rope through the windings on the drum, leading to shock loads and possible damage to the hoist rope.”

This issue is something that is recognised throughout the lifting industry. IC spoke to Dave Hewitt, application specialist at Bridon, manufacturer of wire ropes, who discussed an alternative method to overcome this problem.

“Traditionally, when employing long lengths of rope for lifts at large tension differences, a simple ‘safe’ rule is never to spool a rope off a winch drum at a tension that is greater than twice the tension at which the rope was spooled on to the drum. However, there are numerous variables that should also be taken into account for application specific accuracy. Such variables include rope diameter, rope construction, and the number of wraps and layers. Bridon recommends that such factors are always taken into account.

“One alternative method to spooling rope on to a single winch drum is to utilise a twin capstan traction winch in conjunction with a storage winch. Passing the rope around the dual capstans diminishes the tension in the rope, which reduces the tensile imbalance between the rope winding on and the rope winding off winch drum. This method can also reduce spooling and crushing damage that can occur in cross-over zones when employing multi-layer spooling.”