A Study of Lightning Current Distribution at a Wind Turbine Foot

—Influence on Current Measurements Using a Rogowski Coil—

Abstract

A Rogowski coil, used for measuring lightning current through a wind turbine generator system, is generally set up at the foot of a tower. In most wind turbines, there is an entrance at the foot of the tower, which leads to a flight of stairs or a ladder. When lightning strikes the wind turbine, the lightning current flows to the ground through the blades, nacelle, and tower. The current is shunted to the tower and the stairs/ladder at the foot of the tower, from where it may flow into the foundation and the earth. A Rogowski coil is usually set up at only the foot of a tower. The lightning current shunted to the stairs/ladder cannot be measured using the Rogowski. The installation position of the Rogowski coil depends on the construction of the stairs/ladder. In this study, the lightning current distribution at the foot of a tower is calculated using the FDTD (Finite Difference Time Domain) method, which is one of methods used for numerical analyses of electromagnetic fields. We also studied the effect that the setup of the stairs/ladder and the resistivity of the ground have on the lightning current distribution. The results of the current distribution are very important for predicting the total current that flows through an existing wind turbine generator system.