Prediction of geomagnetically induced currents in power transmission systems Original Research Article

Geomagnetically induced currents (GIC) in technological systems are a manifestation of space weather at the Earthʹs surface. In power systems GIC cause saturation of transformers, which may even result in a collapse of the whole system and in damage of transformers. Predictions of GIC could help power systems operate smoothly through large geomagnetic disturbances. In physical modelling the key quantity is the geoelectric field at the Earthʹs surface. Efforts aiming at a reliable physical GIC forecasting should thus concentrate on the determination of the electric field, in particular in extreme storm conditions containing rapidly varying ionospheric currents. The method of calculation of the electric field should not simplify the geophysical situation too much but it should permit fast computation. Recently, new techniques based on the complex image method (CIM) have been developed, which are accurate and fast. This paper describes the applicability of CIM to GIC forecasting. A westward travelling surge (WTS) event is considered in detail, and the GIC produced in the Finnish high-voltage power system are determined.