Geomagnetically induced currents in power transmission systems

The Finnish power system

The Fingrid Oyj company and FMI/GEO have collaborated in investigations about GIC in the Finnish 400 and 220 kV power systems since 1977. The Finnish system has not encountered significant GIC problems but the northern location of the country, together with changes in the structure of the power system, imply that GIC investigations should be continued in Finland.

Recordings of GIC have been performed in the earthing wires of some 400 kV transformer neutrals. Special studies, based on theoretical modelling and measurements,about GIC occurrence in the Finnish high-voltage systems have been carried out in 1985, 1986 and 1987. A larger project with GIC recordings at fivesites, including a transmission line, was arranged in 1991 to1992. It enabled the derivation of accurate statistics of the probabilities and durations of GIC events at all 400 and 220kV sites. Such statistics are usable for the planning and designing possible countermeasures to avoid problems by GIC.

At the moment there is going on a project implemented to study the impact of largest possible magnetic storms on the Finnish power system. Various ionospheric current models and IMAGE-magnetometer network is used to find out the most harmful GIC distributions in the Finnish power system. The main purpose is to find out the largest possible total currents in the system. This quantity is closely related to the reactive power demand and thereby to the stability of the Finnish power system.

See animation of modeled GIC in the Finnish power system during passage of a westward traveling surge (WTS) and animation of modeled GIC during a westward electrojet event.

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