Lightning protection of CFRP wind turbine blades - What is the dominant cause of failure: Specific energy or charge?

Abstract

This paper investigated which component of a lightning strike is responsible for the majority of damage in Carbon Fiber Reinforced Plastic (CFRP) by investigating the strength loss induced by the exposure to two different electric current waveforms. The two waveforms used were the 10/350μs waveform simulating the first return stroke during a direct strike according to IEC 61400-24 Ed1.0 and the second was a unipolar long stroke component. CFRP strip specimens were manufactured and subjected to the two waveforms of electric current to simulate a lightning strike event. After exposure, specimens were extracted from the CFRP strips, and then loaded in compression and shear to determine the residual strength remaining. The compression tests were conducted on uniaxial coupons and loaded in accordance to ASTM standard D6641. Shear tests were conducted on V-notch specimens and loaded in an Iosipescu test rig in accordance to ASTM standard D5379. The results of the tests were compared to CFRP coupons, which were not exposed to any electrical current. A comparison between undamaged specimens and damaged specimens was made to determine which has more effect on the strength degradation; electric charge from the long stroke component or specific energy from the first return stroke. The results show that impulse current has more impact on strength degradation than a unipolar long stroke current.

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ORCID for T.M. Harrell: orcid.org/0000-0002-0783-533X

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