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Blades on collapsed turbine may have spun too fast

Investigators at the Klondike III wind farm east of The Dalles believe the huge blades on a wind turbine that collapsed and killed a man were spinning too fast.

The collapse killed 34-year-old Chadd Mitchell from Goldendale. The father of three was inside the top of the turbine, performing a 500 hour service inspection.

“While investigation is not yet complete, based on the information we have so far, there are indications that what we call an ‘over speed operation’ may have occurred after a sequence of procedures performed during the service inspection,” said Siemens spokesperson Melanie Forbrick.

“Over speed” means the wind turbine is operating at speeds above normal parameters, said Forbrick.

Siemens is the company that built the wind turbine which suddenly collapsed Saturday afternoon.

Forbrick confirmed workers at the scene reported after the incident that the blades of the wind turbine were spinning out of control.

“What would occur would be similar to a ceiling fan spinning on high – it would be similar to that,” Forbrick said.

Oregon OSHA investigators spent Tuesday at the scene and are investigating the “over speed” incident.

“We’ve heard that and are looking into the possibility of excessive vibration,” said Oregon OSHA spokesman Kevin Weeks.

Weeks said state investigators would work with engineers from the Siemens company, but will also draw on outside experts to maintain objectivity.

Tuesday Siemens investigators searched for and found a black box device held in the nacelle, the capsule at the top of the wind turbine.

A second “controlling” computer sits at the base of the turbine’s tower and has also been recovered.

Fobrick said engineers will analyze both computers to reconstruct exactly what happened inside the turbine before its collapse.

“That will help us understand why and how the machine could have been in this mode”, she said.

The company spokesperson said early indications suggest there was nothing wrong with the wind turbine itself.

“The over speed operation indicates the root cause of the collapse is not a tower issue,” said Forbrick.

“We’ve found nothing to indicate there’s a structural design issue with that tower,” she said.

Forbrick pointed out Siemens has 6,400 similar wind turbines operating around the world.

None, she said, have snapped in half like the turbine east of The Dalles.

By Pat Dooris


28 August 2007