Magnetic diffusion method of predicting geomagnetic induced voltage

Induced dc currents due to geomagnetic storms have caused power system blackouts and transformer damages in the past. Statistically, geomagnetic storms follow a 10-11 year sunspot cycle, but large storms with significant geomagnetic induced current (GIC) impacts can occur at any time. This paper presents a method of estimating the magnitudes of terrestrial voltages which is based on solving the magnetic diffusion equation. The method predicts the oft-quoted figure of “1 volt per kilometer” for the range of geomagnetic field variations (magnitudes and frequencies) and ground resistivity frequently encountered. The magnetic diffusion method is validated by the plane wave method.