More technical problems at flagship project -- Vestas weighs option of dismantling all turbines at Horns Reef

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Vestas is considering bringing all 80 wind turbines at the Danish Horns Reef offshore wind farm ashore to carry out repairs to faulty transformers, generators and correct "other small things," confirms the company's managing director, Svend Sigaard. The Vestas V80 2 MW machines were installed two years ago 14-20 kilometres off the west coast of Denmark in the North Sea.

The news that Vestas may take the blades off each machine and bring the turbine nacelles back to shore surfaced last month in a prospectus released by the publicly traded company prior to its long planned capital increase. The brief reference was followed by a statement by Danish utility Elsam, the owner of the 160 MW Horns Reef station. The generator problems have not been widely known about until now, but the transformer problem has been openly discussed since autumn 2003. The replacement of all transformers was started earlier this year (Windpower Monthly, March 2004).

"The harsh conditions on the North Sea have made work difficult," says Elsam. For this reason Vestas may prefer to carry out the more comprehensive repairs which now appear necessary under "optimal conditions" on land. "It is important that Vestas, as responsible supplier, takes action as fast as possible," Elsam states, adding that the goal is to complete the entire retrofit by the autumn. The utility's financial loss will be minimal, due to Vestas' warrantee on technology and availability. Elsam declines to comment further.

Generator windings

Sigaard says the newest trouble has been discovered on some of the generators, all of which were supplied by ABB. Vestas is still assessing the number affected. A production fault leading to loose generator windings has caused some generators to break down, says Sigaard. The company is working with ABB to repair the damage.

The longer standing problems with the transformers, also supplied by ABB, have been further localised, adds Sigaard. While Elsam described the combination of factors that lead to the transformer breakdowns in detail three months ago -- including insulation thickness, ventilation placement and under-dimensioning of components for the site's extreme wind conditions (Windpower Monthly, March 2004) -- Sigaard says that all involved parties are not completely in agreement about the reasons for the failures, other than that "they are due to a short-circuiting in the transformer, which has not been sufficiently insulated for the very salty environment in which the turbines are placed. In other words, it's a problem that insulation will solve." ABB declines to comment.

Problem seen before

The insulation fault is similar to that experienced with Siemens transformers in 12 of the 20 Bonus 2 MW wind turbines at the Middelgrund offshore station near Copenhagen. All of the transformers were exchanged, most of them in 2001.

In all of the faulty Middelgrund transformers the insulation thickness was found to be 2.5 millimetres at the point of the short circuit; the supplier's manual stipulates it should be eight millimetres. After failing to reach an agreement with Siemens, the owners of the Middelgrund station decided to replace the Siemens transformers with transformers from ABB, but of a different type than those used at Horns Reef. Insulation on the new transformers was increased to six to eight millimetres. The capacity of the transformers was also upgraded to 2.5 MW, which has significantly lowered both operating temperature and their temperature variations.

Furthermore, Danish utility Energi E2, which owns ten of the 20 Middelgrund turbines, moved all the transformers to the bottom of the towers, where the environment is dry and controlled and free from machine vibrations. The remaining ten machines are owned by a local co-operative, Middelgrundens Vindmøllelaug.

SAME supplier

Bonus managing director Palle Nørgaard says that at the newer 165 MW Nysted offshore wind station, which Bonus installed last year for Energi E2, the company uses the same ABB 2.5 MW transformers used at Middelgrund and the same installation technique. No transformer problems have been experienced there, he says. Nysted is the second big offshore demonstration plant constructed under an agreement between the Danish government and the country's utility sector.

While the Middelgrund owners moved from Siemens to ABB as transformer supplier, Vestas is exchanging about two-thirds of the ABB transformers with units from Siemens, with the rest coming from Starkstrom-Gerätebau (SGB), also a German company. Sigaard says it is news to him that the damaged Siemens transformers in the Middelgrund turbines were replaced with ABB units. Although there appear to have been discussions between Bonus and Vestas about the transformer problems, it could be that Vestas has not been made aware by Siemens that it did not solve the transformer problems at Middelgrund, says a source.

Sigaard stresses that Vestas has still not decided whether it will dismantle the Horns Reef turbines and sail them to shore for repair. In addition to the transformers and generators faults, there are "several other different small things" that need adjustment or repair, he says.

In its 181 page prospectus released last month, Vestas mentions the Horns Reef problems in three short paragraphs. It states it is trying to "identify how difficulties involving certain principal components can be remedied, including the possibility of performing part of the work onshore," adding that "if these difficulties prove to be greater than expected, they could have an adverse effect on the group's business, financial condition and results of operations." Otherwise the prospectus states that management does not expect the situation at Horns Reef "to have a material adverse impact on the group's financial results."

Repair costs for transformers alone have been estimated by external sources to run between DKK 400,000 and DKK 750,000 per turbine, mounting to a total of DKK 32-60 million (EUR 4.3-8 million), plus production losses to Elsam. The cost of fixing the generator problem and any further repair work is not known.

The Vestas 2 MW turbine was type-approved for offshore use by Germanischer Lloyd (GL) of Germany, which certified the entire machine as complying with specified design criteria in December 2001, confirms GL's Axel Andrea. He declines to comment further on the faults experienced by a wind turbine with full GL approval.

Vestas in Britain

The troubles seen at Horns Reef have not been observed on the Vestas 2 MW turbines installed in the British offshore wind station at North Hoyle towards the end of last year. John Warren of project developer National Wind Power (NWP) says much of the Horns Reef problems were known before the North Hoyle turbines were installed. "Remedial work was able to be done before they went out," he says of the turbines.

"The technology is notionally the same but that does not mean that the components are from the same source," says Warren. NWP has requested information from Vestas on what the problems at Horns Reef might mean for North Hoyle, where all 30, V80 machines are now installed and under commissioning. "We are getting that information. We have good communication with Vestas," Warren says. "Our view -- without having the full details back from Vestas -- is that there is very little at Horns Reef that would relate to North Hoyle." The Vestas 2 MW is also being used by PowerGen at Scroby Sands, an offshore project of 30 turbines off the east coast of England, currently being installed.


How well Vestas handles the problems, both technically and in relation to its customers and suppliers, will be the key for whether Vestas can maintain its lead in the burgeoning UK offshore wind industry, according to Gordon Edge at the British Wind Energy Association. Edge says it is difficult to tell yet whether the Horns Reef problems will adversely affect the fledgling UK market for offshore wind power, particularly because any future UK projects using Vestas machines will use 3 MW V90 wind turbines.

"The issue for UK developers will be more about how Vestas goes about fulfilling its obligations to Elsam," says Edge. "Problems happen, but if they are fixed well then people should have some reassurance. A parallel can be drawn with how GE dealt with the problems that affected its 9F gas turbines in the late 1990s. That said, if too many problems were to happen in too many projects, any turbine company would be in trouble. Hopefully Vestas will be able to learn from the experience and prevent that from happening."

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