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 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.

Differential Magnetometer Measurements of Geomagnetically Induced Currents in a Complex High Voltage Network

“…Indirect measurements of GICs are also possible. For example, the differential magnetometer method (DMM) was first applied to pipelines by Campbell () and Pulkkinen et al () and adapted later for HV power lines (Matandirotya et al, ; Viljanen & Pirjola, ). With DMM, a magnetometer placed under a HV line detects the background magnetic field plus the excess quasi‐DC current flow during strong geomagnetic activity, while the magnetic field measured at a remote site records only the natural variation.…”

Quantifying the Performance of Geomagnetically Induced Current Models

“…When it comes to evaluate the performance of a given model, one is faced with the question of what is the most suitable method to compare it with real observations (in the case of GIC in power grids, the currents measured directly in the transformer neutrals by using Hall effect transducers; e.g., Torta et al, ; or those indirectly obtained by differential magnetometry under power lines; e.g., Matandirotya et al, ). The broader community studying SW impacts is actively discussing how to evaluate model performance across a variety of prediction domains (e.g., Bruinsma et al, ; Liemohn, Ganushkina, et al, , Liemohn, McCollough, et al, ; Morley, Brito, et al, , Morley, Welling, et al, ; Shim et al, ; Welling et al, ; Wintoft & Wik, ).…”

“…In order to provide additional information to the skill score P , we recommend its combined use with the correlation coefficient r as a minimal set of performance metrics. We note that it is still a relatively common practice to use the latter statistic alone to test the effectiveness of the model in predicting the data (e.g., Bailey et al, ; Butala et al, ; Mac Manus et al, ; Marshall et al, ; Matandirotya et al, ; Torta et al, ; Viljanen et al, ). However, r accounts neither for scaling factors nor for shifts between the two series, which is a clear weak point of it.…”

Detecting Geomagnetically Induced Currents in Electric Power Transmission Lines

“…Figure 5-5 shows the application of the Hanning smoothing window on the data measurements. Comparing the simplified sensing system with results obtained by [39] results in an R-value improvement from between 0.5 and 0.8 to 0.99 (consideration of test bench vs real world). The simplified system was found to be 97.7% accurate compared with the ideal calculated values from the Biot-Savart law.…”

“…The first method is to deploy a hall-effect sensor mounted on a transformer neutral-to-ground wire, which requires specialized training and provides limited visibility of GIC flow, as described in [38]. The second method is to deploy a differential magnetometer technique, that requires external synchronization and complex sensors as described in [39].…”