A 100 metre high wind turbine collapsed because of a fault in its system for controlling the blades, the company said.
No-one was injured when the giant structure worth about £2 million unexpectedly buckled and hit the ground, scattering debris across a wide area of mountainside in Northern Ireland earlier this year.
It was one of eight turbines on the Screggagh wind farm located between Fintona and Fivemiletown in rural Co Tyrone. The turbines were supplied by Nordex UK.
Doreen Walker, director of Screggagh Windfarm, said: “Nordex has concluded its interim investigation and confirmed that this was a unique fault concerning the wind turbine blade control system.
“This has not been previously seen in the Nordex fleet, and is applicable only to turbines of a similar generation to those provided for Screggagh wind farm.
“Following identification of the failure mechanism, Nordex has immediately implemented an additional protective measure to exclude any reoccurrence of this incident.”
Screggagh wind farm will become operational again from tomorrow.
It is understood the rotor blades spun out of control and the sound of the mechanical structure crashing to the ground could be heard up to seven miles away. Some people compared it to an explosion while others claimed to have heard the sound of grinding metal throughout the day.
Parts of the turbine – which had a tower height of 60 metres, an 80 metre rotor diameter, and an overall base to blade tip height of 100 metres – became embedded in the ground some distance from the main structure.
Wind speeds were “medium” measuring about 10 or 12 metres per second at the time.
Ms Walker said: ” The wind turbine had been in uninterrupted operation for almost four years. Debris from the collapsed wind turbine fell mainly close to the turbine and all contained within the wind farm site boundary.
“The furthest debris was 264 metres from the turbine. No debris fell on to the public road or neighbouring/adjoining land holdings.
“The wind farm site’s precautionary health and safety alert processes worked as intended with local emergency services alerted and in attendance within minutes of the incident taking place. There were no injuries and no personnel on site at the time of the incident.”
She said the site had been completely shut down since the collapse on January 2 so Nordex could complete a full investigation into the remaining seven wind turbines at the site and confirm that they are safe to operate.
Ms Walker added: “Nordex technicians have now performed a series of rigorous tests of the safety systems on all remaining turbines, and have confirmed that all of the turbines comply to design specifications and are now safe to restart.
“These test results have been reviewed by our independent consultants, DNV GL, and they too are satisfied that all of the turbines have passed all tests.
The £26 million wind farm was officially opened in March 2011.
It generates approximately 50,000,000 kW hours a year, enough renewable energy to power almost 11,927 homes a year.
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