Blade test by electrocution -- Lightning strikes

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Lightning strikes are an ongoing problem for wind plant operators. In Germany last year, 20 direct lightning strikes were recorded by the 908 wind turbines registered in the German Wind Energy Measurement Program, which is run by the Institute for Solar Energy Research (ISET). A further 49 cases of indirect lightning damage were also recorded. The average length of time needed to effect a repair was 35 hours.

Manufacturers are constantly striving to protect wind turbines from lightning damage. LM Glasfiber has carried out a test program on a full-scale blade in the world's biggest indoor high-voltage laboratory, subjecting the blade to a 2.7 million volt "strike." The 35 metre blade was suspended from several cranes, allowing it to hang freely in the laboratory at different attitudes. The "lightning strikes" were aimed at different locations on the blade, such as mid-span and the tip. Receptors were embedded in the blade which served to conduct the energy produced by the lightning from the blade to the turbine. Various configurations of these receptors were tested.

According to Troels Sørensen, an engineer at the Research Institute for Danish Electric Utilities (DEFU), who acted as a consultant, the test results make it possible for LM to become the first company within the industry to document the efficiency of its lightning protection systems in accordance with internationally recognised procedures.

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