Influence of spatial variations of the geoelectric field on geomagnetically induced currents

The geoelectric field driving geomagnetically induced currents (GIC) has complex spatial variations. It follows that different patterns of the field vectors in a given area having the same regional mean can produce very different GIC. In this study, we consider a few power grid models and calculate GIC due to a modelled geoelectric field with a regional mean magnitude of 1 V/km. Altogether 8035 snapshots of the electric field are included. We also assume two different ground conductivity models, of which the simpler one consists of two layers across the whole region, and another model has four different two-layer blocks. As a measure of GIC, we use the sum of currents at all substations of the power grid. We also consider the distribution of GIC at a single site. For a given grid, differences between the two ground conductivity models are small. When comparing different power grid models, the sum of GIC varies relatively more for a grid with a small number of substations and transmission lines. When the area and the number of substations increase, the relative difference between the smallest and largest GIC sum decreases. In all cases, assuming a spatially uniform electric field leads to a reasonable estimation of the GIC magnitudes, but it does not produce the largest GIC sum. For a single substation, there is a large variety of GIC values due to different electric field configurations.