Broken turbine blade problem found
Friday, June 01, 2012 8:01 PM
PAYNE - After an investigation lasting more than a month, the manufacturer of the wind turbine blades which failed at the Timber Road Wind Farm in Paulding County has determined a cause.
An investigation into a damaged wind turbine revealed the cause was a defect in the manufacturing of a blade. (TB file photo)
Documents filed Friday with the Ohio Power Siting Board (OPSB) by Vestas and by EDP Renewables show the cause of the failure of one of the blades to be a defect in the manufacturing of that single blade.
"Vestas has concluded that the root cause of the failure of the initial blade was due to a wrinkle in the carbon fiber of the spar (the support structure of the blade)," the report reads. "This wrinkle caused damage to propagate to the point of failure after the blade experienced high loads for a low number of cycles."
On April 24 at approximately 12:48 p.m., a single blade of a turbine located along Paulding County Rd. 70 broke and struck the tower while rotating. That breakage was picked up by a sensor and the turbine immediately shut down. However the turbine was quickly restarted remotely by a Vestas technician working at the monitoring station in Portland, Oregon. As it was restarted the two remaining blades began to rotate, but after a few revolutions a second blade struck the tower and scattered debris in the surrounding fields. EDP personnel were on the scene by 1:20 and contacted Vestas which put the turbine into a paused state.
Although the failure of the first blade appears to be from a manufacturer defect, that is not the case with the second blade. According to the report, "Vestas has also concluded the second blade failure was the direct result of an overload caused by failure of the first blade. In other words, had the first blade not failed the second blade wold not have failed."
The report from EDP states that the turbine manufacturer has not yet been able to confirm whether any other blades in the Timber Road Wind Farm are affected by the same defect. However by April 30 Vestas had inspected and formally approved the blades of 53 of the remaining 54 turbines to return to service with the remaining turbine showing blade damage unrelated to the incident. That damage has since been repaired.
The report noted, "These failures are the first of this kind on the v100 turbine in North America.When the Times Bulletin spoke with an official with EDP Renewables nearly two weeks after the incident, he pledged to keep the wind farm shut down until it could be deemed 100 percent safe. Now, with approval of the OPSB, the turbine blades of Timber Road Wind Farm could begin turning again soon.
Any restart of the 55 turbines would be done in Load Reduced Mode (LRM), an alternative operation mode designed to reduce the loading on the blades. "For operational wind speeds, the operational extreme load levels are reduced, on the average, by more than 30 percent compared to the design load level," the report states. "This means that by using the Load Reduced Mode, the risk of blades breaking is dramatically reduced, as any damage in the blade remains at its current level."
In addition to operating in LRM until all the loose ends of the investigation can be tied up, EDP is also making adjustments in its operations including eliminating the ability to remotely restart a turbine after the specific sensor alarm that occurred April 24 is set off. Blades will also be inspected by representatives of the manufacturer on a monthly basis, and if any further issues are found the turbine will immediately be shut down for further investigation. Loads on the blades will be monitored to be sure LRM is functioning effectively.
In its request to restart, EDP states that it plans to restart approximately 15 turbines each consecutive day to confirm the effectiveness of operating in LRM, and if any issues arise all running turbines will be shut down for further investigation.
The Timber Road Wind Farm is made up of 55 Vestas v100 1.8 megawatt turbines, each of which is located in Paulding County.