https://hdl.handle.net/10646/289 2026-04-20T13:01:09Z https://hdl.handle.net/10646/4014 Differential magnetometer method applied to measurement of geomagnetically induced currents in Southern African power networks Matandirotya, Electdom; Cilliers, Pierre J.; Van Zyl, Robert R.; Oyedokun, David T.; de Villiers, Jean 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. 2016-03-18T00:00:00Z https://hdl.handle.net/10646/4013 Modeling geomagnetically induced currents in the South African power transmission network using the finite element method. Matandirotya, Electdom; Cilliers, Pierre J.; Van Zyl, Robert R. Geomagnetically induced currents (GIC) are a result of time variations of the geomagnetic field,which induce a geoelectric field at the Earth’s surface. Geomagnetic perturbations are enhanced during adverse space weather events called geomagnetic storms. All ground-based conductor networks can be affected by GIC during such events. As a way of assessing the magnitude of GIC expected in a particular technological system, models are developed, in which the computation of the induced geoelectric field isa key step. Computation of GIC in the South African power transmission network has so far been done using a uniform Earth model and improved using a layered Earth conductivity profile. In this work we present geoelectric field results obtained by using the finite element method (FEM) and improved GIC estimates using a realistic conductivity profile, magnetic field data interpolated from two South African observatories,and a new method for estimating the network coefficients,a and b, which map the north-south and east-west electric fields to their respective GIC components. The performance of the chosen FEM model demonstrates that it is an effective tool for GIC modeling. Unlike previous engineering techniques, our method for estimating the a and b coefficients from GIC and measured magnetic field data gives results that are independent of prior knowledge of the network configuration. The GIC estimated using the a and b coefficients obtained from the proposed method compares well with the measured GIC during the late October 2003 geomagnetic storm. 2015-03-24T00:00:00Z