Effects of Lightning on Pultruded Carbon Fiber Wind Blades

Modern wind turbine blades incur occasional damage from lightning strikes. In non-conductive glass laminates, lightning damage causes severe charring, and is often obvious from visual inspection. In conductive carbon laminates, lightning strikes do not always result in visible damage, and the impact on strength and fatigue resistance is uncertain. Thus, it is difficult to evaluate a carbon fiber wind blade suspected of receiving a lightning strike. This experimental study investigates the effect of electrical current running longitudinally through pultruded carbon fiber wind blade specimens. Testing simulated the worst 1% of lightning strike in terms of peak current, time to peak, and action integral, and the worst 50% of lightning strike in terms of charge transfer. Post-test, specimens were inspected using nondestructive inspection (NDI) methods and were then mechanically tested for ultimate tension and compression, and tension-tension fatigue. Results show that carbon fiber pultrusions withstand severe lightning currents with no visible or NDI-indicated damage. Preliminary structural tests show a decrease in ultimate compressive strength at the most severe lightning test case.