Wind turbines need to be built high to be effective but this makes them a magnet for lightning which can be disastrous –– and nothing a modern lightning rod has been able to solve. While some damaged wind turbines can be upcycled into glorious tiny homes (yes, we’d be happy to review a sample!), investors in turbine projects expect a return on investment.
Lightning strike on an unprotected wind turbine blade can raise its temperature to as high as 54,000° F (30,000° C), and result in an explosive expansion of the air within the blade. This expansion can cause delamination, damage to the blade surface, melted glue, and cracking on blade.
A team from Korea has developed the world’s first technology to prevent damage caused by “positive lightning,” which frequently occurs in offshore wind farms during winter.
Just as voltage has positive and negative poles, lightning also has positive and negative polarities. When clouds carry a positive charge and the ground carries a negative charge, positive polarity lightning strikes, while the opposite case results in negative polarity lightning.
About 90% of the lightning strikes that occur are negative polarity lightning, while positive polarity lightning occurs with a relatively low probability. However, positive polarity lightning has a much higher current intensity, increasing the likelihood of causing major accidents.
Additionally, positive polarity lightning primarily occurs in winter when the altitude of clouds is lower.
With the recent increase in demand for renewable energy, the construction of wind turbines has also been on the rise. In particular, in South Korea, there is a growing trend of large wind turbines specialized for low wind speed environments being moved offshore. However, offshore wind farms are highly vulnerable to lightning strikes from thunderclouds because the turbines are tall and there are few other structures around.
Damage to the blades (rotors) caused by such lightning strikes can lead to the shutdown of wind turbines, resulting in significant losses, including repair costs.
KERI’s achievement is the development of a new edge receptor to protect wind turbine blades from positive lightning.
Currently, wind turbine blades are equipped with an air-termination system, a type of lightning rod that attracts lightning strikes to minimize damage. However, this system has low protection efficiency against positive lightning. Positive polarity lightning has a highly irregular pattern and a much higher current, requiring more advanced technology for effective protection.
Researcher Woo Jeong-min’s team conducted in-depth research on various polarities and conditions, and thoroughly analyzed the effects of the blade’s rotation angle and material. As a result the team found that, unlike negative polarity lightning, positive polarity lightning strikes the side edges of the blade, bypassing the air-termination at the tip and causing damage.
This happens because the positive charge in the air accumulates near the air-termination, and the positive polarity lightning, having the same charge, avoids it and strikes the middle part of the blade, which carries a negative charge.
The research team created a scaled-down model to thoroughly analyze the blades affected in these specific lightning vulnerability areas, and repeatedly conducted artificial lightning experiments using high-resolution cameras to accumulate data. They also used precision measurement systems and simulation technologies to replicate various blade rotation angles and environmental conditions during the experiments.
Through this, the research team was able to design a new edge receptor that optimally positions the air-termination along the side edges of the blade. They confirmed that this method can control the charge distribution of positive polarity lightning, minimizing the damage.
“With our technology, we will greatly contribute to improving the stability and efficiency of wind turbines, promoting the expansion of renewable energy, and ultimately have a positive impact on reducing electricity bills for consumers,” says Jeong-min
The results of this study are published in Results in Engineering.
