Prediction of extreme geomagnetically induced currents in the UK high-voltage network

Geomagnetically Induced Currents (GIC) can be damaging to high-voltage power transmission systems. GIC are driven by rapid changes in the strength of the magnetic field external to the Earth's surface. Electric fields are produced in the ground by the interaction between this changing magnetic field, the sea and the conductivity structure of the Earth. Using a technique known as the thin-sheet approximation, we can determine the electric field at the Earth's surface, which in turn allows the calculation of GIC in the earthing connections of high-voltage transformers within a power grid. We describe two new developments in the modeling of GIC in the UK, though the results are applicable to GIC-related research in other regions. Firstly, we have created an updated model of the UK surface conductivity by combining a spatial database of the UK geological properties (i.e., rock type) with an estimate of the conductivity for specific formations. Secondly, we have developed and implemented a sophisticated and up-to-date model for the 400 kV and 275 kV electrical networks across the whole of Great Britain and, in addition, the 132 kV network in Scotland. We can thus deduce the expected GIC at each transformer node in the system based on the network topology from an input surface electric field. We apply these developments to study the theoretical response of the UK high-voltage power grid to modeled extreme 100year and 200year space weather scenarios and to a scaled version of the October 2003 geomagnetic storm, approximating a 1 in 200year event.