The Influence of 3-D Earth Conductivity, Geoelectric Field Polarization, and Power Grid Topology on GIC Risk

Geomagnetically induced currents (GICs) are naturally occurring electrical currents that flow through the Earth and long conductive infrastructure, such as power lines, during geomagnetic storms. GICs in the electric power grid can cause damage to electric power transformers, system failures, and wide-scale blackouts. Here, the combined effects of the power network's topology and the Earth's underlying conductivity structure on GIC risk are examined using examples from the electric power grid in Alberta, Canada. Our results show that the electric field polarization generated by geomagnetic storms is strongly dependent on the subsurface conductivity structure. Moreover, due to Earth induction effects, the two components of the transverse electric fields can also be highly correlated in specific geological regions. Combined, this creates a preferred electric field directionality, presenting a GIC risk for power grids with specific directional topology. A direct comparison between the geoelectric field and the measured transformer neutral-to-ground (TNG) currents measured near Edmonton, Alberta, on 24-04-2023 is shown. At this location, the two horizontal components of the geoelectric field are strongly correlated, and (Formula presented.) and (Formula presented.) show strong temporal and waveform correspondence with the TNG current. Two truth tables illustrate the increased or decreased GIC risk in such cases demonstrating that the GIC in a segment of the electric power network may combine constructively or deconstructively depending on the power network configuration and the relative orientation of the geoelectric field polarization. This is further exemplified by a case study of two real-world network configurations in central Alberta.