Lightning Ground Potential Rise - A Contributing Factor to Damage Associated with Wind Turbine Blades

The international standard IEC 61400–24, addressing specifically lightning protection of wind energy systems, was introduced in 2010 with a revision and update of the standard published in 2019. This international standard presents guidance, through high voltage and high current tests, on the specific evaluation of wind turbine blades against lightning damage. Despite this guidance, a significant number of blade-damage-cases are still being reported, making it an important consideration in view of the growing number of wind farms employed in renewable energy projects worldwide. This paper indicates that lightning ground potential rise, including travelling waves and reflections from the foundation of the wind turbine and other bonded parts of the wind turbine, can set up potentials inside the blade that are large enough in magnitude to cause the breakdown of the composite material which the blade is manufactured from. Potentials set up in this manner are not tested for under the existing test regime covered by IEC 61400–24. The paper further shows the importance of earthing / bonding and protection of specific components, such as sensors, heating systems and carbon strips applied in the blade. When not done correctly, the implication includes mis-assignment of the lightning protection zone inside the blade, as recommended by secondary standards / specifications, and an underestimation of the lightning risk associated with the wind turbine blades. Based on the findings of this paper, it is strongly recommended that the testing techniques covered in IEC 61400–24 should be updated to incorporate the anticipated damage mechanism presented by ground potential rise (and associated travelling waves and reflections). This will require some form of model of the entire tower plus the foundation and accompanying soil conditions.