A 60-m-high wind turbine snapped in two in the early morning during a storm. The upper 55 m of the turbine fell to the ground, scattering debris over a fairly large area and driving the rotor into the ground. Firefighters set up a cordon. The operator shut down the wind farm’s seven other wind turbines and hired a security firm.
The operator and the turbine manufacturer conducted an investigation. The turbine had been commissioned in 2003. Three days before the accident, while the wind was blowing at more than 40 m/s, the turbine’s pitch control system failed. This caused the turbine to stop automatically. As the weather conditions made it impossible to go up the turbine, the situation was diagnosed remotely. Due to a data interpretation error, a technician moved the turbine to a position that caused the rotor to quickly increase in speed past the safety limit. The overspeed protection system activated, but abnormal wear on the brake blocks of the pitch control system prevented the turbine stopping. This subjected the tower to mechanical loads that greatly exceeded the turbine’s design limits and caused it to collapse. The operator’s investigations revealed that the mechanical linkage between the motor and the brakes was not covered by the maintenance inspection protocol. As a result, the accumulated wear had not been detected during the annual inspections.
The other turbines at the wind farm were restarted after checking them for specific issues and replacing the brake blocks on their pitch control systems. The operator:
- revised the procedure to follow in the event of failure of the blade pitch control system and trained their maintenance technicians accordingly.
- updated the maintenance instructions for this system (now, each brake block must be replaced in whole or in part once every five years);
- implemented a specific tool for diagnosing potential failure of the brake blocks (it compares the actual position of the blades to the reference position);
- sent a safety memo to wind-farm operators who use the same type wind turbine.