  As reliance on power networks has increased over the last century, the risk
of damage from geomagnetically induced currents (GICs) has become a concern to
utilities. The current state of the art in GIC modelling requires significant
geophysical modelling and a theoretically derived network response, but has
limited empirical validation. In this work, we introduce a probabilistic
engineering step between the measured geomagnetic field and GICs, without
needing data about the power system topology or the ground conductivity
profiles. The resulting empirical ensembles are used to analyse the TVA network
(south-eastern USA) in terms of peak and cumulative exposure to 5 moderate to
intense geomagnetic storms. Multiple nodes are ranked according to
susceptibility and the measured response of the total TVA network is further
calibrated to existing extreme value models. The probabilistic engineering step
presented can complement present approaches, being particularly useful for risk
assessment of existing transformers and power systems.
