Benchmarking the Swedish Power Grid Against a 1-in-100-Year Geoelectric Field Scenario

Abstract. Sweden's communication and power systems have been impacted by extreme space weather events in the past. For instance, the May 1921 storm caused a fire at the telegraph and telephone station in Karlstad, and the 2003 Halloween storm led to a blackout in Malmö. In this study, we present the first comprehensive assessment of the potential impacts of a 1-in-100year event on the entire Swedish power grid. Using magnetic field observations from the 30 October 2003 event as a baseline, we constructed two extreme scenarios. In Case 1, we used the observed magnetic field across Fennoscandia. In Case 2, we assume a spatially uniform ionospheric current system, producing identical magnetic waveforms across the country. Then the estimated 3D electric field was scaled using region-specific scaling factors derived from recent statistical analyses of electric field extremes in Sweden. The scaled geoelectric field and power lines voltages are computed using the recently developed RAISE model, which includes realistic ground conductivity and power line topology. Our results show that the strongest horizontal electric fields, around 12 V/km, occur within the 55° and 58° MLAT band, particularly in regions with sharp lateral conductivity gradients. East–west-oriented power lines are especially vulnerable, as they align with the dominant orientation of the induced electric field. Overall, during the peak of a 1-in-100-year geomagnetic storm, more than 100 transmission lines are expected to experience voltages above 50 V multiple times over the course of the substorm. At the peak of the strongest disturbance, triggered by a sudden weakening of the westward electrojet, around 100 lines are expected to exceed 100 V. These results provide critical insights into infrastructure vulnerability under extreme space weather.