Comparing the Impact of HEMP Electric Field Waveforms on a Synthetic Grid

A nuclear bomb detonated above the earth's surface can cause a high altitude electromagnetic pulse (HEMP). HEMP's create an electric field at the earth's surface, which induces unwanted slowly varying dc currents on transmission lines. To evaluate a power grid's vulnerability to HEMP's, two electric field waveforms have been used, having peak electric fields of 24 volts per km and 40 volts per km. Recently, a report was released containing six time-varying electric field waveforms and justified using a peak electric field of 84.57 volts per km. This paper compares how the magnitude of each electric field waveform is affected by different 1D conductivity regions. In addition, the impact of each electric field on a 10,000-bus synthetic grid will be evaluated. Analysis of the new waveforms show that there is not a single worst-case waveform. Different electric field waveforms have characteristics that affect the grid in varying ways. It is recommended that comprehensive HEMP vulnerability studies be done with multiple waveforms.