Calculation of Voltages in Electric Power Transmission Lines During Historic Geomagnetic Storms: An Investigation Using Realistic Earth Impedances

Commonly, one‐dimensional (1‐D) Earth impedances have been used to calculate the voltages induced across electric power transmission lines during geomagnetic storms under the assumption that much of the three‐dimensional structure of the Earth gets smoothed when integrating along power transmission lines. We calculate the voltage across power transmission lines in the mid‐Atlantic region with both regional 1‐D impedances and 64 empirical 3‐D impedances obtained from a magnetotelluric survey. The use of 3‐D impedances produces substantially more spatial variance in the calculated voltages, with the voltages being more than an order of magnitude different, both higher and lower, than the voltages calculated utilizing regional 1‐D impedances. During the March 1989 geomagnetic storm 62 transmission lines exceed 100 V when utilizing empirical 3‐D impedances, whereas 16 transmission lines exceed 100 V when utilizing regional 1‐D impedances. This demonstrates the importance of using realistic impedances to understand and quantify the impact that a geomagnetic storm has on power grids. Key Points The use of empirical 3‐D impedances produces significant spatial variability in the voltages that are calculated across transmission lines Calculation of voltages across transmission lines during the March 1989 storm shows numerous transmission lines exceeding 100 V Integrating over transmission lines does not always reduce the influence of spatial geoelectric variability caused by realistic impedances