Multi-megawatt plants struck by lightning more than ten times a year
Lightning strikes to wind turbines are not uncommon. According to the industry portal Windbranche, each wind turbine is struck by lightning 0.6 to once a year on average - usually on a rotor blade. The risk is even higher for multi-megawatt turbines. Studies show that these are exposed to direct lightning strikes at least ten times a year. No wonder, due to their exposed location on hills or off coasts, wind turbines attract lightning particularly strongly. Strikes can have serious consequences - from repair-related failures to the destruction of the entire plant.
What happens when lightning strikes
When lightning strikes a wind turbine, currents of several tens of thousands of amperes flow within fractions of a second - even maximum values of 200,000 amperes have already been recorded. The electrical voltage reaches several million volts.
If the lightning protection now fails, the consequences are serious: Not only can overcharge damage occur in the electrical control system, but the rotor blades can also snap off. And not only that. Since the air temperature inside the lightning channel rises abruptly to several tens of thousands of degrees Celsius, fires easily start.
This is why wind turbines are susceptible to fires
We know from experience: Fires have devastating effects on wind turbines without functioning lightning protection. This is because wind turbines are mainly made of carbon fiber composites. Although the material is particularly light, it has very poor electrical conductivity. Without lightning protection, the energy of lightning can poorly dissipate into the ground, and the system takes damage, which can cause high costs.
The consequences of lightning strikes for wind turbine operators
The consequences for wind turbine operators are severe: in 2019, the European research and development information service cordis put the annual damage caused to operators by lightning strikes at 1.5 million euros. In addition to repair costs, this also includes lost revenue.
How to reliably protect wind turbines against lightning strikes
To avoid these damages and costs, reliable lightning protection is needed. Lightning protection systems are used to divert incoming electrical current into the ground, protecting rotor blades or nacelles from damage.
The complete lightning protection system of a wind turbine consists of the external lightning protection system and the surge protection system. The external lightning protection is realized by receptors as well as arresters, which conduct the lightning current into the ground via defined paths.
How lightning protection systems for wind turbines worked
Lightning protection of wind turbines concerns the protection of two subsystems: Rotor blades and mechanical drive train with gearbox and generator. Verification of the protective effect is the subject of DIN IEC 61400-24. The standard recommends that the lightning current resistance of protection systems be verified by high-current tests with a lightning impulse current and long-term current.
Lightning protection systems must ensure that lightning is safely "captured" by the lightning receptors of the rotor blades and discharged to the grounding system via the natural components such as bearings, machine supports, tower and/or the surrounding systems such as spark gaps or carbon brushes.
Here's how to use lightning protection systems effectively
To ensure that lightning is reliably discharged, we deploy lightning protection systems at our customers' facilities that effectively protect bearings as well as gearboxes and generators. These systems route the current past the bearings and divert it from the blade to the tower into the ground.
Turbine manufacturers install our lightning protection systems on the rotor bearing and on the azimuth bearing on which the nacelle rotates. Some users mount additional lightning protection carbon brushes on the shaft of the blades.
Due to the low rotational speed, the wear of our carbon brushes is very low, so they have a service life of three to five years. During maintenance work, we recommend that plant operators regularly check whether the carbon brushes move freely in the brush holder. If this is not the case, they cannot fulfill their function in the event of a lightning strike and must be replaced.
How wind turbines can withstand the challenges of the future
As a long-standing partner to the wind industry, we know: The demands on wind turbines and future turbine generations are increasing. On the one hand, thunderstorms are becoming more frequent as weather extremes increase. On the other hand, wind turbines are increasingly being installed off-shore and in remote regions. Both factors increase the risk of lightning strikes.
To ensure that our customers are protected against damage and expensive plant breakdowns in the future, we have successfully tested other of our components for high-current transmission for their suitability as lightning protection components in accordance with DIN IEC 61400-24 in addition to our classic lightning protection systems. This means that we can provide you with designs for almost all installation conditions at short notice.
"Lightning conductor" for wind turbines rethought
And we're thinking even further ahead. Carbon materials are lightweight materials with excellent electrical and thermal properties. We are currently working on projects with leading manufacturers of blades for wind turbines to implement these advantages over significantly heavier metals in "lightning conductors" on the blades. The background: The higher weight of metal has negative effects on the dynamics of air movement (turbulence) on the blade and on noise generation. This effect can be avoided or at least greatly minimized with lighter components.