Historically Large Geomagnetic Storms and Potential Electric Power Grid 
Impacts

John Kappenman
Metatech - Applied Power Solutions Division

While recent work has been done to examine the possible Dst Intensity
of historically large geomagnetic storms, the impacts caused to modern
day electric power grids from these storms occurs due to rapid
rate-of-change of regional geomagnetic fields which in most cases are
driven by large ionospheric electrojet current intensifications.
These temporally and spatially dynamic disturbance morphologies are
not well-characterized by Dst or other broad geomagnetic storm
indices.  For estimates of storm intensity that correctly scale the
threat potential to electric power grids, it is necessary to describe
the rate-of-change of geomagnetic field.  The rate-of-change of the
geomagnetic field (dB/dt usually measured in nT/min) creates at ground
level a geoelectric field that causes the flow of
geomagnetically-induced currents (GIC) through ground connection
points in electric power grids.  An overview will be provided of
observations of historically large geomagnetic storm events and the
potential for impacts on modern electric power infrastructures.