Wind turbines are an increasingly popular form of energy generation. Although dependent on size, their ability to potentially power a home for two days with a single rotation (opens a new window) has contributed to a 9% YoY growth of total installed wind capacity to 906 GW in 2022, according to the Global Wind Energy Council (opens a new window). However, a recent incident in the UK where a wind turbine shed blades highlights the changing weather conditions that designers have to address when looking at the extremes of weather.
In December 2023, the blades of a 34-metre (110 foot) wind turbine in Galston, Ayrshire, broke off and flew through the air (opens a new window) during storm Gerrit. While there were no injuries or other damage, such accidents may happen more often in future as both the frequency and severity of storms increase due to climate change.
Potential loss drivers
Manufacturers engineer the hub of wind turbines to withstand the potential loading forces for the average and an excessive wind speed over a defined period. However, as the centrifugal force on the blades increases, the structure’s sensitivity to overspeed also rises.
Wind turbines are a complex engineering feat, and there are many reasons why a blade failure may happen:
Tensile stress throughout the blade due to excessive centrifugal forces.
Poor quality control, lack of maintenance and component failure.
Failure to monitor the turbulence level (caused within a cluster of turbines) that is the main cause of fatigue loads of many major components, including blades. The height and positioning of the wind turbine are an important factor for turbulence levels.
Climate change makes wind levels less predictable and potentially more forceful.
Hail (amongst other examples of impact damage) can strike the leading edge of the blade as it rotates.
In colder climates, the blade can get loaded with ice, causing an imbalance that could lead to a blade failure.
Weather causing wear to the leading edge of the blade, hail, rain, sand, etc.
Repairs carried out to blade damage, without balancing causing a stability issue at speed.
The blade control and emergency stop systems that are not tested routinely
Lightning strike to blades causing delamination, not affecting blade balance at standard operating conditions (These may not be detected until a post loss investigation).
Defects during manufacture, causing delamination, root (connection to hub flange) failure, etc.
Claims impact
The costs to remediate the detachment of blades from an onshore wind turbine can vary due to several factors:
Larger turbines require specialist cranes to access the hub and the blade replacements, creating delay in the return to operation because of the high lift crane’s availability and location.
Lifting of the blades is also dependant on the wind conditions around the turbine at the time. A limitation is usually placed on safe lifting due to wind speeds.
High rope access to the blades left in place to ascertain if they have been impacted by the material thrown from the detached blade.
The investigation of the possible damage to the Nacelle due to the vibration on the hub with a single blade detachment at high velocity and cost of repair to the Nacelle and tower.
The costs depend on the location – offshore and onshore, remote and local. Onshore turbines offer easier access for lifting equipment or climbing gangs, but can still be in difficult to access locations.
Risk mitigation
The risk of a failure can be inherent within the manufacturing process and a full manufacturing quality document should be supplied and inspected by or on behalf of the client, especially as the blade length increases. Increasing the focus on servicing and adjusting the maintenance regime should contribute to reducing the risk of an incident. Appropriate, regular servicing and checks (particularly on the overspeed system) can play a major role in detecting any potentials issues early. The overspeed protection system is maintained by a monitoring system that will look at vibration, speed, and axial displacement of the turbine rotor, with an increase in blade speed limit to ward against overspeed. If necessary, the electronic monitoring system will take an executive action to slow the speed of the blades down, by altering the angle of the blades related to the wind and applying a shaft brake.
Wind turbines generally require preventative maintenance checkups two to three times per year, particularly on the nacelle (containing the gearbox, generator, brake, and the low or high-speed shafts). The blades should undergo a visual inspection at least every two years for potential damage, but monitoring of weather condition in the location of the turbines should determine if a more regular inspection should be implemented. The life cycle of the turbines installed should also be considered in the same way as other items of equipment to avoid ‘running to failure’.
As more wind turbines are installed there will be an increase in the number of turbine failures. Good quality control on the design and build and good maintenance and inspection of the installed turbines can ensure that the frequency of failures, as a percentage of the overall numbers in service, can be maintained at a low level.
For more information, please visit the Lockton Energy and Power page (opens a new window), or contact:
Philip Hewer, Risk Engineer
E. philip.hewer@lockton.com
Paul Clarke, Risk Engineer
E. paul.clarke@lockton.com
