Geomagnetically induced currents (GICs) are electric currents that flow between the ground and power lines via transformers as a result of interactions between the solar wind and the Earth's magnetic field. Transformers are not built to handle GICs, which manifest as slowly-varying DC, and can sustain damage and suffer operation problems when the GICs become too large or continue over longer periods. The most extreme outcome resulting from large GICs in recent decades was the complete collapse of the Hydro-Quebec power grid in Canada in March 1989. During a period of intense geomagnetic storm activity, one transformer near Quebec overheated due to the presence of large currents and burned out, leading to a cascade of tripping transformers and a province-wide power outage that left six million people without power for nine hours. Extreme events like this do not happen often, but can have far-reaching consequences when they do. Hence it is very important to study the development of GICs specific to a region to determine the real impact and threat.
Measurements of GICs at multiple points of the power grid in Austria have been ongoing since 2014. In most cases and during geomagnetically quiet times, the currents do not go above 1-2 A, however there have been measurements of GICs during abnormally active times that exceed 14 A. In Scandinavian countries, where geomagnetic variations are much larger and the threat of large GICs is also greater, currents in the range of 200 A and higher have been observed.
The study of GICs in Austria through computational modelling started at the ZAMG in 2015. The model takes measurements of the geomagnetic field from the Conrad Observatory along with data on the local ground resistivity in Austria to compute how currents are induced in the Austrian power grid. This model has been iteratively improved over time by comparing the results to the measurements of actual GICs, and has a good level of accuracy for prediction purposes.
The results of studies of GICs in Austria along with extreme case scenario studies in particular have been summarised in the following two papers:
Bailey, R. L., Halbedl, T. S., Schattauer, I., Römer, A., Achleitner, G., Beggan, C. D., Wesztergom, V., Egli, R. & Leonhardt, R. (2017), Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach, Annales Geophysicae 35, 751, https://doi.org/10.5194/angeo-35-751-2017
The work described here was carried out in the framework of the FFG project GEOMAGICA (Geomagnetically induced currents in Austria) with the project number #847986.