Heat response of unipolar lightning impulse and DC current component conducted through CFRP samples used for wind turbine sparcaps

Lightning protection of wind turbine blades has reached much attention due to the increased number of blade manufacturers now featuring blade designs that include conductive Carbon Fiber Reinforced Polymers (CFRP) composites for structural components. CFRP materials are stiff and lightweight, but exhibit material properties different from other conductive materials like metals, making them more susceptible to lightning damage. The weaknesses observed is governed by the limited electrical and thermal conductivity, transverse to the fibers, the anisotropic material properties, and the integration of the CFRP into the overall WT blade or aerospace structure.
This study investigates in detail the heat response on CFRP material exposed to two different components of a lightning strike; the unipolar impulse current and the direct current (DC). The first waveform examined is a unipolar 10/350?s waveform simulating the first return stroke during a direct strike according to IEC 61400-24 Ed1.0 , the second being a unipolar long stroke component also defined by the IEC standards. Both current components are tested using the conducted current test method provided in Annex D3.4 of IEC 61400-24 Ed1.01.
CFRP strips made with vacuum assisted liquid resin infusion were exposed to conducting currents as defined above using the two different waveforms. A PYROVIEW 640L IR camera was used to monitor the heat response of each sample. The data from the center of the sample was used to collect the heat response and the results can be seen in Figure 1 and Figure 2. This data helps determine thermal response models to help determine damage from thermal degradation due to electric current.