A freedom of information request has led to the publication of hitherto unseen documents which explain why two wind turbines crashed to the ground during unexceptional weather conditions.
The findings of the restricted reports suggest that the first incident was caused by a design shortcoming, while the other was due to installation error.
The investigations have prompted the Health and Safety Executive to work with wind turbine makers to improve safety standards and collect accident and incident data, encouraging them to share best practice through the industry.
The HSE was called in to investigate the collapse of two wind turbines in 2013. The first involved a 40m Gaia GW133 11kW wind turbine at Winsdon Farm in North Petherwyn, Cornwall. Initially, suspicion fell on design features to combat the hazards associated with rotor over-speed, but these were found to be suitable and sufficient.
Eventually the investigation led HSE inspectors to consider the securing arrangements for the tower, which were found to be susceptible to fatigue failure.
The report said: “The most likely cause of the failure lies in the limited design margins offered by the detailed design of the securing arrangements at the tower base on the first-generation design.
“The margins available in this design didn’t appear to offer sufficient resilience to the combined fatigue loading and stress concentration effects that might be expected, particularly when other factors such as poor site choice and reduced product quality came into the equation.”
Meanwhile, a second report looked into the collapse of a 50m Endurance E-3120 50 kW wind turbine at East Ash Farm in Bradworthy, Devon.
In this instance, HSE said that the most likely cause of the incident was failures to the foundation rods caused by “a significant deviation by the installers from the prescribed tower base design and installation process”. This, it said, had resulted in “increased fatigue loading, which promoted premature failure of the securing rods”.
According to HSE, Gaia Wind and Endurance Wind Power put in place remedial plans to ensure that design and installation shortcomings were addressed. It said: “We instructed the companies to examine similar installations and take any necessary action. This work has now been completed.”
HSE has said that dialogue with the wind turbine industry is ongoing. It added: “We are working with RenewableUK, the principal trade association, providing valuable
input to its health and safety initiatives at strategic and working levels. We are supporting their initiative to collect accident and incident data that will be beneficial in enabling industry benchmarking and the sharing of information.”