The Relationship Between the Magnetometer Data Derived GIC Index and Measured GIC in High Voltage Transformers in Australia

Abstract Geomagnetically induced currents (GICs) are telluric currents driven by space weather that can adversely impact high voltage transformers in electricity supply networks. It is often difficult to obtain transformer GIC data so ground based magnetometer data may be used to estimate the transformer GIC via complex modeling of both network and ground conductivity parameters. Alternatively, the impacts of GICs are often inferred from the time derivative of the horizontal components of magnetometer data, d b /dt. Using measured GIC data from transformers in the eastern Australia electricity supply network during the May and October 2024 storm time intervals, the correlation with d b /dt, a model geoelectric field, and a plane wave approximation (the GIC “index”) were compared. The maximum correlation coefficient with d b /dt was 0.7 compared with 0.97 for the time dependent version of the GIC “index.” For mainland Australian latitudes, correlation coefficients larger than 0.9 were found for transformers located up to 1,000 km away from the magnetometer. These distances decreased for magnetometers at higher latitudes located in Tasmania. The results show that the plane wave based GIC “index”, suitably weighted by component, is better than d b /dt for predicting transformer GIC.