Transmission Line Corridor Shape Effect on Geomagnetically Induced Currents Using 3-D Earth Conductivity Models

Severe Geomagnetic Disturbances (GMDs) pose a potential threat to the United States bulk electrical system. To assess the system impact, a method to calculate geomagnetically induced currents (GICs) in a power grid using the EPRI 1-D earth conductivity models has been introduced by the NERC reliability standard TPL-007. Under this method, transmission lines are modeled as straight lines between substations. Alternatively, magnetotelluric impedances that reflect the 3-D earth conductivity structure have recently become available in much of the U.S. thanks to the work of the National Science Foundation sponsored Earthscope program. The new 3-D method provides geoelectric fields with much higher resolution than that obtained from the 1-D models. This paper studies the impact of the actual transmission line corridor shapes using 3-D and 1-D methods on a fairly large-scale power system. The study used an actual storm that took place on 07-08 September 2017.