Using Detailed Ground Modeling to Evaluate Electric Grid Impacts of Late-Time High-Altitude Electromagnetic Pulses (E3 HEMP)

High-altitude electromagnetic pulses (HEMPs) are magnetic field fluctuations generated by nuclear bombs detonated above the earth's surface. They have the potential to disrupt the power grid by inducing geomagnetically induced currents (GIC) on transmission lines. The magnitude of the GIC highly depends on the conductivity of the earth hundreds of thousands of meters beneath the surface. This paper describes a method to calculate HEMP electric fields using the one-dimensional (1-D) conductivity model, in which the earth is modeled with flat layers of varying thicknesses and conductivity levels. This method applies the 1-D conductivity model by modifying a publicly available HEMP electric field originally calculated under the uniform conductivity model. The electric fields resulting from each model have significant differences in magnitude and locational sensitivity. A comparison of these electric fields and their impact on a power system is presented using a 10 000 bus synthetic grid.