Wind farms are a great way to harness the energy nature provides without burning fossil fuels, providing a cleaner energy source. However, harnessing wind power also comes with a danger nature affords us: lightning.
Because of the high energies involved, a lighting strike to a turbine can be devastating - unless suitable protection is installed.
Lightning damage to wind turbines is often due to inadequate or insufficient bonding from the ends of the blade to ground, but with an operations and maintenance (O&M) program that includes proper grounding and periodic inspections, downtime due to damage will be reduced or even eliminated.
Lightning strikes, on average, deliver 55kWh of energy and as much as 1.1MWh. Without proper lightning protection, this much energy can cause structural damage up to catastrophic failure of your system, leading to very expensive repairs, or unproductive downtime.
They become more common as the height of these structures increase, putting wind turbines located on hills at an even bigger risk. Unfortunately, there is not a 100% effective way to avoid a potential lightning strike, but steps can be made to guard your turbines against the threat of lightning.
In order to protect against lightning damage, the structure must have a virtually unimpeded resistance path to ground. This begins with lightning receptors attached to the outside of the blades with an internal conductor leading the path to the base of the platform and eventually into the ground.
As with any metallic object, corrosion will have a detrimental impact on the conductive properties of the material. Which is why the lightning protection system must be verified routinely to make sure that the resistance of the conductor is low enough to carry the fault current safely to ground when lightning strikes.
The turbine manufacturer will set the specific test limits (typically <30 mΩ), that ensure the connection is in a condition to handle fault currents.
A continuity test is not enough; it won’t give any indication to the quality of the connection. To measure the resistance of the lightning conductor accurately, a low resistance ohmmeter is needed, which can give an accurate measured value and produce at least 1A of current at the required resistance range.
In the field, to properly measure the resistance of the blade, a test connection is made from the electrode near the end of the blade to the blade’s root end. Since, the separation between test points can be as much as 100 meters, special measuring techniques need to be employed to eliminate the resistance in the test leads from becoming part of the results. Implementing the Kelvin/Thomson 4 terminal principle will eliminate the measurement error due to lead resistance.
Seaward Group USA has more than 30 years of expertise in developing high precision low resistance meters, and for more than 10 years, the wind industry has been relying on our meters for accurate measurements, to keep their systems and people safe.
We offer free online product demonstrations of all of our testers and free online product support so you can get the most from your tester.
Take a look at our test kits below and get in touch if you would like to discuss how they can help you with your wind turbine lightning protection testing.
Our DO4002 Kit features a lightweight (2lbs) handheld ohmmeter, a 3-meter HandSpike lead and a custom Kelvin Clamp lead (60m, 80m or 100m in length) supplied on a portable reel.
The DO7 Kit features a rugged ohmmeter housed in a hard shell plastic case to protect against wear and tear of life on a utility wind farm, a 3-meter HandSpike lead and a made to order custom Kelvin Clamp lead (60m, 80m or 100m in length) supplied on a portable reel.
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