Poor service behind dramatic accidents -- Exploding turbine video

After several hours in overspeed operation a runaway wind turbine in mid-Denmark dramatically fell apart in windy weather late last month, an event captured on home video. Within hours the video was being circulated worldwide on the internet, causing a deal of consternation about public safety in the vicinity of wind power stations. Since the 1980s, however, runaway incidents have become rare events as the industry has matured.

The ten-year-old turbine in question was a 600 kW model produced by Nordtank Energy Group before that company merged to form NEG Micon, which was subsequently absorbed into the Vestas empire. Poor service has initially been blamed for the atypical incident, in which both the turbine's mechanical brake and tip brake system failed.

The publicity created by the "exploding turbine" video, broadcast on web news sites and national television, prompted a rash of equally dramatic questions to climate and energy minister Connie Hedegaard. She has requested that Vestas reassure the public about how it will prevent a repeat of the accident, in which sections of the machine's blades were flung several hundred metres. Police had cordoned off the area to a distance of 400 metres and nobody was hurt.

On the day of the turbine disintegration, Vestas' head of communications, Peter Kruse, told television viewers that there were strong indications that poor service of the wind turbine rather than the technology was at fault. "We must face the fact that the bottle is pointing at us," he added, with reference to a popular "spin the bottle" party game.

The country's wind turbine owners association immediately asked all its members to ensure that quality service was being carried out on their machines at the intervals specified by maintenance experts. Thirty years ago, the association successfully pressured for all wind turbine blades to be equipped with tip brakes, which are automatically released if the rotor starts overspeeding. Today the requirement is standard for type-certified wind turbines. But as the association points out, tip brakes only work if they are not rusted solid or broken off. It recommends an annual tip brake test.

Exacerbating the public relations problem for wind power in Denmark, a Vestas turbine on the other side of the country shed a blade the morning after the disintegrating Nordtank drama on February 22. The blade was thrown 100 metres from a Vestas 660 kW machine installed in 2000, without causing injury. A turbine of the same model collapsed in Scotland on November 8 during heavy winds (Windpower Monthly, December 2007). The reason for the loss of the blade in Denmark has been put down to insufficiently tightened bolts. Similar human error was blamed for the loss of a blade from a Vestas NEG 850 kW turbine in Sweden in January. That machine had been running since 2002.

The Danish owners association has asked Vestas for copies of the detailed analysis reports from the Danish accidents when they are available. Until such time, association members are requested to study the service reports on their wind turbines and contact the service company or the association's technical advisors if they have reason for concern.

"Finally, we must stress that these accidents are sensational also because in recent years they are rare occurrences. Today there are more than 5000 turbines turning in Denmark. It would be out of proportion to change the law because we've seen two accidents within a few days of one another," says association director Asbjørn Bjerre.

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