Differential magnetometer method applied to measurement of geomagnetically induced currents in Southern African power networks

Abstract

Geomagnetically induced currents (GICs) in conductors connected to the Earth are drivenby an electric field produced by a time-varying magnetic field linked to magnetospheric-ionosphericcurrent perturbations during geomagnetic storms. The GIC measurements are traditionally done on theneutral-to-ground connections of power transformers. A method of inferring the characteristics of GIC inpower lines using differential magnetic field measurements is presented. Measurements of the GIC in thepower lines connected to a particular power transformer are valuable in the verification of the modelingof GIC in the power transmission network. The differential magnetometer method (DMM) is an indirectmethod used to estimate the GIC in a power line. With the DMM, low-frequency GIC in the power line isestimated from the difference between magnetic field recordings made direc tly underneath the power lineand at some distance away, where the magnetic field of the GIC in the transmission line has negligible effect.Results of the first application of the DMM to t wo selected sites of the Southern African power transmissionnetwork are presented. The results show that good quality GIC measurements are achieved through theDMM using Commercially- Off-The-Shelf magnetometers.