Distributed-Source Transmission Line Theory for Modeling the Coast Effect on Geoelectric Fields

Geomagnetic effects on man-made ground-based systems are an increasing concern such as power grids, submarine cables, pipelines, and railway systems. Assessing the threat to these systems requires calculating the geoelectric field induced at the Earth's surface during geomagnetic disturbances and using this as input to a system model to determine the electric currents flowing across the system. Calculations of the geoelectric fields need to take account of lateral variations in conductivity that can affect the geoelectric field at and near discontinuities such as the coast. This article presents a new method for modeling the influence of coast effect on geoelectric fields based on a generalized thin sheet model but develops a solution derived from distributed-source transmission line theory. Transmission line segments are converted to equivalent-pi circuits which are held together to compose a nodal admittance network representing the Earth's surface and underlying crust. Inversion of the admittance matrix combined with magnetic source fields then determine the geoelectric field profile across the coast. Two cases are presented to show how the DSTL theory is applied to different Earth conductivity models. Calculation results are compared with numerical solutions obtained from FEM, which confirms the accuracy of the DSTL theory for computing geoelectric fields.