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

Geomagnetically induced currents (GICs) in conductors connected to the Earth are driven by an electric field produced by a time‐varying magnetic field linked to magnetospheric‐ionospheric current perturbations during geomagnetic storms. The GIC measurements are traditionally done on the neutral‐to‐ground connections of power transformers. A method of inferring the characteristics of GIC in power lines using differential magnetic field measurements is presented. Measurements of the GIC in the power lines connected to a particular power transformer are valuable in the verification of the modeling of GIC in the power transmission network. The differential magnetometer method (DMM) is an indirect method used to estimate the GIC in a power line. With the DMM, low‐frequency GIC in the power line is estimated from the difference between magnetic field recordings made directly underneath the power line and 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 two selected sites of the Southern African power transmission network are presented. The results show that good quality GIC measurements are achieved through the DMM using Commercially‐Off‐The‐Shelf magnetometers. Key Points Geomagnetically induced currents Magnetic field measurements