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Solar storms and the power grid

How geomagnetic storms induce currents in power lines, what happened in Quebec in March 1989, and how US grid planning standards address the risk. Sourced to NOAA, NERC and peer-reviewed analysis.

The mechanism: geomagnetically induced currents

During a geomagnetic storm, electric currents high in the atmosphere change quickly. Those changing magnetic fields induce an electric field in the ground, which drives slowly varying, quasi-DC currents through long conductors such as high-voltage transmission lines. These are called geomagnetically induced currents (GICs). [1]

In large transformers, GICs can push the magnetic core into saturation. NOAA describes the consequences: local heating that can damage the transformer, distorted waveforms that can trip protective equipment, and extra reactive load that can threaten voltage stability on a grid already near peak demand. [1]

Historical impacts

Telegraph systems suffered anomalous currents in the 19th century, and power-grid effects were first reported after a storm in March 1940. NOAA's list of later impacts includes the nine-hour Hydro-Québec blackout and a transformer loss in March 1989, and a blackout in Sweden in October 2003. [1]

Boteler (2019) reconstructed the March 1989 event. It was driven by two CMEs, and the Hydro-Québec collapse came early in the storm, during a sharp substorm, before the storm index reached its peak. In other words, the timing of rapid field changes mattered more than the overall storm size. [2]

How the risk is managed

In North America, NERC Reliability Standard TPL-007 requires transmission planners to assess how their systems would perform under defined benchmark geomagnetic disturbance events and to develop corrective action plans where needed. [3]

Operators get advance notice from NOAA SWPC's watches, warnings and alerts, which are tied to the G scale. The DSCOVR spacecraft at L1 typically gives 15 to 60 minutes' warning of a CME shock arriving. [4] [5]

This page is general education only. For operational decisions, use NOAA SWPC products and your system operator's procedures.

Sources

  1. NOAA SWPC: Electric Power Transmission (space weather impacts) https://www.swpc.noaa.gov/impacts/electric-power-transmission
  2. Boteler, D. H. (2019). A 21st Century View of the March 1989 Magnetic Storm. Space Weather. doi:10.1029/2019SW002278
  3. NERC Reliability Standard TPL-007-4: Transmission System Planned Performance for Geomagnetic Disturbance Events (PDF) https://www.nerc.com/pa/Stand/Reliability%20Standards/TPL-007-4.pdf
  4. NOAA SWPC: NOAA Space Weather Scales https://www.swpc.noaa.gov/noaa-scales-explanation
  5. NOAA SWPC: Coronal Mass Ejections https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections

Sources were checked on 2026-10-21. Text on this page is original. Quoted figures are attributed and linked to the source. General education only, not for safety or operational decisions. Disclaimer.