Lightning Protection Optimization for Large Wind Turbines with Method-of-Moments Florian Krug, Ralph Teichmann General Electric - Global Research Freisinger Landstrasse 50, 85748 Munich, GERMANY Ulrich Jakobus, Niels Berger EM Software & Systems GmbH Otto-Lilienthal-Str. 36, 71034 Böblingen, GERMANY Hans Steinbigler, Josef Kindersberger Laboratory for High Voltage Technology and Power Transmission, Technische Universität München Arcisstr. 21, 80290 München, GERMANY Abstract: - Electro-magnetic fields adjacent to the lightning current path in wind turbine generators are analyzed. The method of moments is used to analytically describe the transient distributed electro-magnetic field caused by a lightning strike. A simulation tool using the method of moments is presented. The electro- magnetic field distribution during a lightning strike in a wind turbine hub is analyzed in detail. The electro- magnetic field analysis is extended by a statistical lightning risk evaluation for wind turbine generators. Key-Words: - Lightning protection, Method-of-Moments, Wind turbine, Power System, Risk Analysis, Electro-magnetic Field 1 Introduction Lightning strike effect on wind turbine generators have recently become a major concern as the number and the height of wind turbines continue to increase. The impact on wind turbines range from disturbances on control electronics, damages to single components, such as blades or electronic components, to fires resulting in a complete loss of the installation. Most of these effects result in undesirable downtimes with its financial implications for the wind turbine operator. Further costs are added if components need to be replaced. Lightning strike risk analyses for common structures are established procedures to identify sensitive areas and determine the probability and severity of damages caused by lightning strikes. Simple methods [3] and more sophisticated procedures [4] were introduced. Specific guidelines and recommendations to assess and mitigate the risk of lightning damage for wind turbine generators [1] [2] were presented by various international technical committees such as IEC or IEA. These recommendations focus on provision to safely conduct the lightning current thereby avoiding substantial damage. The electro-magnetic implications caused by the large transient lightning currents on control electronic components adjacent to the lightning current path have not yet been discussed. This paper presents an analytical method and a tool suitable for the analysis of direct lightning strike effects on sensitive electronic components in a wind turbine generator. The simulation results for the electric and magnetic field distribution during a lightning strike in a generic hub of a large wind turbine are presented. 2 Risk Analysis An important initial step of a risk analysis is the estimation of the frequency of direct strikes to the wind turbine. This frequency is mainly a function of the lightning activity at the installation site, the local geographical topology and the dimensions of the turbine. The procedure of the estimation is described in [1] and [2]. It is based on investigations and experiences with common structures up to a height of 60 m. As an example a wind turbine with three rotor blades, a hub height of 100 m and blade length of 38.4 m is used. An offshore location with a distance of more than three times the total height of the turbine to the next turbine is assumed.