Geomagnetically induced currents: A measurement based inverse determination of earth impedances

Geomagnetically induced currents (GIC) can lead to serious disturbances in transmission grids. Arising problems range from high noise levels and reactive power consumption of transformers up to transformer outages and regional blackouts. To mitigate GICs effectively, simulation is an important aspect. However, incomplete electrical grid data in combination with discrete earth layer models lead to differences between measurement and simulation. In this article, we describe an inverse calculation method of the complex earth impedance, based on transformer neutral point measurements. We show that the resulting model leads to higher simulation accuracy. This calculation method may be used especially when earth layer data is missing or inaccurate.