In the case of one storm that occurred in 1921, analysts compared its magnetization, or Bh, curves with the Bh curves of more recent storms. Analysis of another storm that occurred in 1859 is based on qualitative and anecdotal evidence of the storm's effects on electrical systems and auroral observations of the northern lights as detailed in news reports that have been preserved.
Extrapolating the effects of those historical incidents to today in light of the effects of smaller but more recent storms gives an indication of how vulnerable today’s infrastructure may be to disruption. For example, in 1989, a geomagnetic storm caused the Hydro Quebec power grid to fail in approximately 90 seconds, causing a nine-hour blackout that left millions without power. According to modeling by Kappenman, if a geomagnetic storm the size of 1921 hit today—approximately 10 times the size of the 1989 event—more than 350 EHV transformers could be destroyed, leaving more than 130 million Americans without power. Given the magnitude of the disruption, restoration could take months if not years, says Kappenman.
The North American Electric Reliability Corporation (NERC), whose mission it is to ensure the reliability of the bulk-power system, considers Kappenman’s modeling too dire, says Mark Lauby, NERC's director of Reliability Assessments and Performance Analysis. NERC is currently working on its own tools so that it can develop, in its view, a more realistic projection of which transformers could fail in such a scenario.
Critics say utilities should harden the most critical transformers, primarily those supplying electricity to cities, in the short term. Utilities should be adding in other protections and redundancies over time.
“[Utilities] can put resistors to ground at the transformers, which will help to reduce the current flow that is induced by geomagnetic storms,” says Yousef Butt, a scientific consultant to the Federation of American Scientists and a physicist at the Harvard-Smithsonian Center for Astrophysics.