Why are long power transmission lines vulnerable during geomagnetic storms?

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Space weather Earth's full North Polar auroral oval, in an image taken in ultraviolet light by the U.S. Polar spacecraft over northern Canada, April 6, 1996. In the colour-coded image, which simultaneously shows dayside and nightside auroral activity, the most intense levels of activity are red, and the lowest levels are blue. Polar, launched in February 1996, was designed to further scientists' understanding of how plasma energy contained in the solar wind interacts with Earth's magnetosphere.

Geomagnetic storms, caused by the interaction between solar wind and Earth's magnetic field, induce electric currents that can enter long-distance power distribution systems. These induced currents are particularly dangerous because they can overload and damage critical electrical transformers.1

When these transformers fail, it often triggers a cascade of power outages across large sections of the electric grid. Because these systems are interconnected over vast distances, a single major storm has the potential to disable a significant portion of a continent's power infrastructure, leading to prolonged recovery times and severe economic disruption.1