Isolated failure and a new prototype -- Vestas 2 MW and 3 MW

Negative publicity for Vestas' flagship 2 MW wind turbine continued last month when the design prototype, installed at Tjærborg Meadow in western Denmark, suffered a major failure on November 4. Human error was behind a control system error, which resulted in the machine running out of control in winds of just 5-8 m/s. The secondary automatic emergency stop system cut in, bringing the turbine to such an abrupt halt that all three blades were severely overloaded and suffered serious damage, reports the company.

"The failure in the prototype's safety system was caused by human error in connection with a retrofit of the turbine's control system," says Vestas. The retrofit was carried out on October 24. As a precautionary measure, Vestas temporarily halted all 80 turbines in the Horns Rev offshore wind plant while the cause of the failure was established. Vestas stresses the failure was an "isolated incident."

The 2 MW turbine was also in the news three months ago when Vestas said it was setting aside an unspecified sum of cash to correct a series of errors, differing from turbine to turbine, on all the 2 MW machines in Germany -- at least 170 according to industry sources. Vestas originally referred to errors on a 1.8 MW turbine, but later confirmed they related to the 2 MW, V-80 model, an offshore version of which is installed at Horns Rev.

Vestas Svend Sigaard calls the errors "teething problems," indicating that the turbine was not exhaustively tested before being released onto the market. He admits that one of the problems has related to the hydraulic pitch regulation of the blades, a much discussed subject in Germany (Windpower Monthly, September 2002). All the known problems with the 2 MW were fixed on the offshore version at Horns Rev before they were set in operation, says Sigaard. The owner of Horns Rev, utility Elsam, says it is satisfied with Vestas. "We've been told that the machines we received have been improved upon," says Jens Bonefeld of TechWise, the Elsam subsidiary in charge of Horns Rev.

The offshore V-80 units are otherwise modified slightly from onshore versions. A different gear box allows for 10% faster blade rotation and the units are equipped with more comprehensive vibration monitoring and corrosion protection. There is a hoist inside each tower for service crews as well as a bivouac room with emergency rations and even a set of playing cards, says Bonefeld. Horns Rev is due for final commissioning next month.

Testing 3 MW units

Meantime, Vestas is installing a whole series of prototypes of its new V-90 3 MW model in three countries. The first was installed in May, 20 kilometres north of Husum, Vestas' base in Germany, and another went up in west Denmark on November 7, at the country's new test centre for wind turbines at Høvsøre.

Also last month, a 3 MW unit was installed at Näsudden on the Swedish island of Gotland in the Baltic Sea for state owned energy giant Vattenfall. Back in Denmark, installation of three more units is starting on December 2 at Stensø, south of Vestas' factory at Nakskov in south east Denmark.

Although Vestas says the V-90 is not yet on the market, not only has it sold one to Vattenfall, but Danish industrial company Danisco owns one of the Stensø turbines. Series production of the machine will not start until 2004, according to Vestas Deutschland. Particular interest is being paid to Vestas' choice of carbon fibre spars for the V-90's 44 metre blades, which makes them as light as a 39 metre blade. Vestas expects to series produce the blades, a new design, in either 2003 or 2004.

The Gotland turbine is the latest step in Vattenfall's experimentation with large scale wind turbines after the utility was forced earlier this year to abandon plans to install ABB's now mothballed Windformer technology (Windpower Monthly, March 2002). The Vestas 3 MW is being installed on the same spot originally designated for Windformer.

Despite the collapse of the ABB project, Vattenfall's Kenneth Averstad says the utility remains firmly committed to wind power. "We've been interested for a long time in developing and testing large wind turbines because we think they will be the future both on land and offshore, and in Sweden the greater potential is offshore." Vattenfall has said it is testing the V-90 for future offshore projects off Sweden's south east coast.

Averstad says Vattenfall will inherit full ownership and rights to the turbine, dubbed Olsvenne II, once it had been tested, which could be this month or next. The machine is sited close to Vattenfall's two other turbines at the site -- a Kvaerner Turbin WTS80 3 MW turbine known as Näsudden II and commissioned in 1993, and a Bonus 600 kW plant installed in 1996. Olsvenne II will increase Vattenfall's combined wind turbine headcount to 42 machines, with a total capacity of 27 MW.

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