The future of lightning risk control

Blade length

Wind turbines are placed in a large variety of diverse environmental conditions around the world. Local changes to topography, lightning intensity, and altitude can have a significant effect to the overall lightning risk to the turbine. Adding to that is the blade configuration where length, reinforcement materials, and lightning protection system (LPS) composition all play a part in how likely a lightning strike is to cause a structural damage.

Increasing the blade length proportionally reduces the relative distance to the lightning cloud; coupled with a high altitude, this adds a risk of the turbine operating within the lightning cloud. An increased focus on utilising high tier composite materials like carbon as reinforcement material does reduce the blade weight and has, for many manufacturers, been the linchpin allowing longer blades above 100 m.

Changing to carbon reinforcements adds more requirements to the LPS; this is due to the conductive properties of carbon and its attractiveness to lightning. This means that during a lightning event, it will interact with the lightning cloud similar to the lightning protection system. In an event where a lightning strike attaches outside of the lightning protection system, it can result in immediate destruction or cause gradual damage that may go unnoticed until it reaches a critical stage. Therefore, addressing the lightning risk for wind turbines is crucial for ensuring their operational efficiency and longevity.

Mitigating the risks

To mitigate the risks associated with lightning strikes, the International Electrotechnical Commission (IEC) has established the IEC 61400:24 standard for lightning protection systems. Compliance with these standards is essential for manufacturers and operators alike to ensure the safety and reliability of wind turbines. The IEC standard provides requirements for testing and certification and guidelines on lightning protection design and lightning protection measures, including the installation of lightning protection systems and sensors to detect and monitor lightning activity. The IEC standard is an important read for any stakeholder in the wind industry with an interest in understanding lightning risk.

Attachment location

Damage propagation of blade damage caused by a lightning strike depends heavily on the location of an attachment. Any lightning damage to the tip area of the blade is in general considered noncritical, providing that the damage is limited to blade shell to trailing edge (TE) debonding. This type of damage is ‘common’ for lightning damages as the lightning strike in its attempt to find the easiest path to ground attached to the receptor cable instead of the receptors. As the cable in many traditional blade designs are located internally in the TE chamber, the lightning strike will pass through the shell and into the cable. In this process the pressure in the chamber will increase due to an increase in temperature inside the chamber. These damages are in the vast majority repairable up tower and does not provide a risk for the continued turbine operation.

More critical is lightning attachments to the blade beam laminate, due to the beam being the main structural component in the blade. In this case, any damage will have a direct effect to the blade integrity. This risk is increased with blade reinforcements made from carbon laminate due to carbon being more brittle and conductive. Any change to the carbon structure can lead to rapid defect development and early failure if not captured in time.

This emphasises the need for effective lightning surveillance and monitoring systems in wind farms.

Lightning surveillance and monitoring

Lightning surveillance and monitoring are two distinct approaches to address the lightning risk for wind turbines. Surveillance involves periodic checks and assessments to identify damages, while monitoring employs real-time data collection to detect and analyse lightning activity continuously. While surveillance is reactive, monitoring offers a proactive solution, enabling operators to take immediate action in re-sponse to changing conditions.

The choice between installing individual sensors on each turbine or implementing a comprehensive sensor network across the wind farm is a critical decision. Individual sensors provide localised information, but a networked approach allows for a holistic view of lightning activity within the entire wind farm. A sensor network enhances the ability to predict and/or manage lightning risks on a broader scale, offering a more effective and integrated solution.

Requirements for either dedicated sensor or sensor network must be made with regards to the risk for the given wind farm due to site conditions or blade configuration.

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