Lightning strikes on wind turbines are very common, as a number of them are located at off-shore or on top of mountains where they are the tallest objects.
Unfortunately, the material used to prepare wind turbine blades, typically glass or carbon fiber reinforced plastics (G/CFRP), can be damaged significantly and hence can cause huge repair costs.
“Typically speaking, anything that slows the flow of lightning through the blade can have catastrophic consequences,” said Oak Ridge National Laboratory’s Vipin Kumar, project leader. “What makes wind turbine blades generally safe during such an event is that the sheer amount of metal strips connected to the lightning arrestors to conduct the lightning quickly into the ground.”
It’s the same effect as what is known as a Faraday cage, perhaps best visualized at science fairs, where a volunteer from the audience stands inside a metal mesh-wire cage that then receives a shock, but dissipates it quickly enough that the occupant feels no shock.
That works well when your turbine blade is made with traditional metals, but as new manufacturing techniques lead to a reduction in the use of metal and increase usage of more (G/CFRP) composites, that process can go awry.
The inherent low electrical conductivity of composites or even significant slowing of lightning’s spread through the blade can have catastrophic results, ranging from damaged electronics to damaged structures.
A team including ORNL researchers and UT students came up with a novel possible solution: Dissipate the lightning quickly by making the blades more conductive.
“The faster we can make lightning dissipate through the composites, the better chance for reduced or no damage to the blades,” said UT’s Pritesh Yeole, a graduate student in the Department of Mechanical, Aerospace, and Biomedical Engineering (MABE). “We knew we had to find a way to speed up that process.”
Along with Yeole, fellow MABE students Tyler Smith and Justin Condon were on the team, joining ORNL’s Kumar, Ahmed Hassen, and Vlastimil Kunc.
The team’s concept is to place 3D-printed highly conductive filaments of copper and graphene on carbon fiber panels, and then simulated lightning strikes on some panels with the adaptation and on some without the new technology so that they could compare results.
By observing the strikes with high speed cameras and examine the panels after they’d been struck, the team saw a better current dissipation performance from the panels that they had altered.
“What we found was that, just as we’d hoped, increasing the conductivity within the panels by adding in conductive filler resulted in significantly reduced damage,” Condon said. “This should help designs moving forward and is especially important as an adaptation for wind turbine blade manufactured with less conductive materials.”
Now that they have proof of concept, Tyler Smith said that the team’s next step is to figure out what combination of conductive polymer works best.