ON THE POSSIBILITY OF PERFORMING STUDIES ON THE GEOELECTRIC FIELD ANDIONOSPHERIC CURRENTS USING INDUCTION IN POWER-SYSTEMS

Geomagnetically induced currents (GICs) flowing in man-made conductors . such as power systems, depend on the integrated geoelectric field in duced by a geomagnetic variation. Thus, in addition to the practical s ignificance of GIC investigations, GICs also provide a means to make l arge-scale electromagnetic induction studies of the Earth and of ionos pheric-magnetospheric current systems. This paper deals with the calcu lation of GICs in the Finnish 400 kV power grid, although the conclusi ons obtained are obviously not restricted to the particular grid studi ed. The treatment is based on a general computer program permitting th e horizontal geoelectric field to be arbitrary. It is demonstrated tha t GICs induced in Sweden have practically no influence in Finland, i.e . GICs do not flow very long distances in the power system. On the oth er hand, GICs are not sensitive to small-scale spatial details of the geoelectric field, which supports their large-scale nature mentioned. Using the present knowledge, a preliminary large-scale conductivity mo del of Finland is also applied here for the estimation of GICs. As an example of nonhomogeneous primary sources describing auroral currents, a sheet current is considered. GICs are recorded at four Finnish tran sformers and at one transmission line for 1 year beginning in June, 19 91. Data collected then will be used also in induction studies accordi ng to the guidelines given in this paper.