GIC occurrences and GIC test for 400 kV system transformer

The geomagnetic induced currents in a transmission network may saturate transformers and cause additional losses, a high level of harmonics, and a lack of reactive power in the grid. Also, malfunctioning of protection circuits is reported in this paper. The field tests made for two 463 MVA system transformers show that tested transformers may tolerate very high DC currents for times typical to geomagnetic storms. The effects of the voltage control and voltage quality in network are also considered, and results of earlier Finnish GIC risk studies are reported.