At around 6 p.m., one of the blades on a wind turbine broke and fell 5 m from the base of the mast. The turbine stopped automatically. The operator was informed by a local farmer, and a technician went to the site to access the damage. The upper part of the mast was damaged by the impact with the blade, although it was not a risk of collapsing. The zone was cordoned off to prevent injury in case of any rotor components fall. Eight other turbines in the turbine farm were shut down. The remaining two, which had recently undergone a complete overhaul, were maintained in operation.
The site was secured the next day. The blade was moved out of the farmed area, and the large debris consisting of composite materials and metallic mechanical elements, thrown over 50 m, were all brought together for inspection and assessment. All of the 54 ball bearings were recovered. As all the small debris was unable to be completely recovered, the farmers of the plots concerned were informed. The storage area for the parts was marked out.
A rupture in the orientation system was determined to be the cause of the accident
The inspection of the mechanical components and the rotor suggests that the blade orientation system had failed. This would have resulted in the rupture of the bearing’s outer ring and then the release of the inner ring integral with the blade. The turbine had undergone a comprehensive maintenance operation in September 2015, and the bearing showed no signs of abnormal wear. However, a series of alarms had occurred on the morning of the event. A hydraulic power unit failure had required intervention by maintenance crews. Following the repair, the turbine has been restarted at about 2:00 p.m.
The operator took the following immediate measures:
- dismantling of the wind turbine involved;
- drafting of an inspection protocol, by the manufacturer, concerning the bearing and threaded fasteners of all the blades before restarting the units that had been shut down;
- inhibition of automatic turbine reset in the event of a malfunction alarm in the blade orientation system;
- limitation of the power produced to 650 kW (instead of 800 kW) for a 7-day observation period.
