Simulation of current distribution in a wind turbine blade using the FDTD method

Abstract

Lightning can pose one of the major natural threats to wind turbines. In special, rotor blades are the most sensitive components to lightning due to their material, constructive nature and movement. Modern multimegawatt wind turbine blades use a combination of glass fiber and carbon fiber reinforced plastic components (CFRP). The last one is electrically conductive and needs to be considered as part of the lightning protection system. In this paper, we present the application of the FDTD method to investigate the lightning current distribution in a wind turbine blade equipped with a 25 m CFRP spar. We found, that for low spar-to-down conductor bonding electric contact resistances, peak currents are higher in the spar, but most of the energy is conducted by the down conductor. The high peak currents in the CFRP would produce intense resistive voltage drops at the connections with the risk of sparks if milliohm connection resistances cannot be achieved. The simulations show that voltages between isolated CFRP laminates of the spar should not pose a threat of sparking if the insulation properties of glass fiber can be ensured in the entire spar. Dangerous voltages between the down conductor and the CFRP spar can occur if the bonding connection at the tip is located far from the end of the spar.