A Study of Transient Magnetic Fields in a Nacelle of a Wind Turbine Generator System due to Lightning

A wind turbine generator system is composed of blades, a nacelle, a tower etc. In recent year, to make the blades and the nacelle lighter, the blades are often made from GFRP (Glass Fiber Reinforced Plastics) and the nacelle is composed of steel grids and GFRP covering it. When the lightning strikes the wind turbine, the current flows into the ground through the down conductor in the blades, the steel grids of nacelle, and the tower. The current flowing near the nacelle produces comparatively large magnetic fields inside the nacelle. Therefore, the communication and control systems are broken down or malfunction. In this paper, the transient magnetic fields in a nacelle due to lightning strokes at the tip of the blade and the rear portion of the nacelle are studied analytically and experimentally. In the analytical studies, the FDTD (Finite Difference Time Domain) method which is one of numerical electromagnetic field analyses is used. The reduced-size model of a wind turbine is used for experimental studies. As the results of the researches, it has been found that the magnetic fields at the front of the nacelle are larger than those at the rear of the nacelle regardless of the injected points of the lightning current. The lightning current following through the down conductor connected to the nacelle through the blades has a strong influence on the magnetic fields in the nacelle. We have proposed that the front of the nacelle should be covered with the conductor plate or mesh to decrease the large magnetic fields.