Transmission Line Modelling of Geomagnetic Induction in the Ocean/Earth Conductivity Structure

Abstract

During geomagnetic disturbances, electric fields induced in the Earth and in power systems, pipelines and submarine cables can interfere with the operation of these systems. Calculations for submarine cables are complicated by the need to consider not just the induction directly into the cable but also the earth potentials produced at the coast at each end of the cable. To determine the coast potentials, we present a new model of the ocean and earth conduc tivity structure that spans the whole length of a cable from one coast to another. Calculations are based on the generalised thin sheet approach introduced by Ranganayaki and Madden but converted to a transmission line model that can be solved using standard circuit theory techniques. It is shown how the transmission line model can be used to calculate the earth potential profile from one side of an ocean or sea to the other. Example calculations are presented for a shallow sea, a shallow ocean, and a deep ocean that are simplified approximations to the North Sea, Tasman Sea and Pacific Ocean and show that the peak potentials occur at the coast. An examination is also made of how the width of a shallow sea and the width of the continental shelf affect these coast potentials. The modelling technique and example results provide a guide for more detailed modelling of geomagnetic induction along the routes of specific submarine cables.