POWER AND PIPELINES (GROUND SYSTEMS)

Geomagnetically induced currents (GIC) in technological sys-tems, such as electric power transmission systems, oil and gas pipelines, telecommunication cables and railway equipment, are a manifestation of space weather at the earth's surface. In power systems, GIC cause saturation of transformers, which may lead to problems in the operation of the system, and even to a collapse of the whole system and to permanent damages of transformers. The best-known GIC effect occurred in March 1989 when the Québec province in Canada suffered from an electric black-out for about nine hours. The corrosion rate may be increased in pipelines when GIC flows from the pipe into the soil, and the associated voltages can disturb pipeline sur-veys and the cathodic protection. This paper summarizes GIC effects on power systems and pipelines. GIC research associ-ated with the Finnish high-voltage power system is discussed. GIC measurement data on a natural gas pipeline and Sweden is presented. The electric field observed at the earth’s surface during a geomagnetic disturbance is the key quantity for the calculation of GIC magnitudes. It depends on currents in the ionosphere and on currents flowing within the earth. The theo-retical modelling of the electric field is discussed in this paper. Particular attention is paid to the complex image method, which permits accurate and fast computations of the electric field and which is thus suitable for time-critical applications like GIC forecasting. 1