A 100-year geoelectric hazard analysis for the U.S. high-voltage power grid

A once-per-century geoelectric hazard map is created for the United States high-voltage
power grid. A statistical extrapolation from 31 years of magnetic field measurements is
made by identifying 84 geomagnetic storms with the Kp and Dst indices. Data from 24
geomagnetic observatories, 1079 magnetotelluric survey sites, and 17,258 transmission
lines are utilized to perform a geoelectric hazard analysis with the most comprehensive
data publicly available. With this data we estimate once-per-century geoelectric fields at
the magnetotelluric survey sites and calculate the theoretical voltages within transmission
lines in the United States power grid. Once-per-century geoelectric field strengths span
more than three orders of magnitude from a minimum of 0.02 V/km at a site in Idaho to a
maximum of 26.8 V/km at a site in Maine, with nearly 30% of the surveyed land area ex-
ceeding 1 V/km. We show the influence that geoelectric field polarization has on geoelec-
tric hazards when viewed on a power transmission network. The calculated transmission
line voltages can exceed 1000 V in some transmission lines. Four regions in the United
States with particularly notable geoelectric hazards are identified and discussed: the East
coast, Pacific Northwest, upper Midwest, and the Denver metropolitan area.