Material fault identified

Five Enercon E40 machines in Hesse have failed this year. The nacelles of two machines recently crashed to the ground, both suffering from a failed "kingpin," a cast iron component used to attach the nacelle to the turbine tower. The material of the failed component in each case was sub-standard, says Enercon.

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Only three more wind turbines could potentially suffer the same fate as two Enercon E40 machines in Hesse that failed earlier this year, according to Enercon's owner, Aloys Wobben. The nacelles of the two machines crashed to the ground within weeks of one another, both suffering from a failed "kingpin," a cast iron component used to attach the nacelle to the turbine tower. The material of the failed component in each case was sub-standard, says Wobben. There is no intrinsic design error, he stresses. Enercon, Germany's flagship wind company, has sold about 1600 E40 machines worldwide.

Wobben says that only three further E40 machines have been identified as having kingpins produced in a batch of five of sub-standard quality. They were supplied by a Spanish foundry which he declines to name. Enercon no longer uses this supplier, relying now on two Germany foundries, in Bavaria and Brandenburg, and one British foundry.

The first E40 failure occurred on January 16 on one of three machines owned by Vogelsberg Windenergie in the Vogelsberg hills (Windpower Monthly, March 1999). Six weeks later the same failure occurred on a turbine at the Windstation Helphershein, also in the district of Vogelsberg. As with the first incident, the nacelle and blades toppled from the tower and crashed to the ground, reports Erich Ruhl of the Vogelsberg local authority.

That same day, March 1, Enercon and the district government agreed to stop all 16 Enercon E40 machines operating in Vogelsberg until safety inspections were complete. The turbines were all back on-line by mid-March, says Wobben. Enercon adds that some of the components were strong enough to largely withstand the impact and are being repaired. The safety inspection was carried out by the Bavarian Technical Association for Inspection (TUEV) of Munich, according to Ruhl.

The control systems of the three suspect machines have been retrofitted with additional software to bring them to a halt should proximity switches detect any untoward movement of the nacelle. In addition a mechanical safety system, "basically bolts," has been fitted to prevent the nacelle from toppling should the kingpin snap, Wobben says. The kingpins of the three machines will soon be replaced, he adds. The retrofit has been approved by Germanischer Lloyd, confirms GL's Christian Nath.

Ruhl stresses that the safety inspections were carried out with "no bad feeling." Communication and co-operation among TUEV, Enercon and the district government has been good, he stresses. The district is concerned that the problems are overcome as soon as possible. The Vogelsberg area has promoted wind energy as a progressive development. It now has 93 turbines operating within its boundaries and views the machines as a trademark of the district.

All costs incurred by the operators of the five machines, including those for lost power generation, will be covered by Enercon, says Wobben. "Even though legally speaking we have sold the machines, we still feel it is our responsibility. We say that our machines will run for at least 20 years, and so they will," he adds. "There will always be room for human error in the production of cast iron parts," he says. "Even greater efforts are being made to maintain high quality. We have had discussions with all the foundry companies."

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