Disastrous space weather risk on large-scale power grid

Geomagnetically induced currents (GIC) flowing in technological networks at the Earth´s surface are ground effects of space weather. During geomagnetic storms, such currents cause bias fluxes in transformers, resulting in half-cycle saturation. Severely distorted exciting currents which contain enormous amounts of harmonics threaten the safe operation of other equipment and even the whole power system. This paper discusses the correlation between current data measured in transformer neutrals and magnetic recordings, and proves that severe vibrations and increased noise phenomena in some transformers are caused by GIC. This paper thus clearly shows that GIC amplitude can be quite large even if in low latitude areas. The fact that calculated results of GIC match well with measured GIC data at the Ling´ao nuclear power plant shows that the Plane Wave Method can satisfy a certain precision in the calculation of the geoelectric field in mid-low latitude regions. Factors increasing GIC risks in China obviously include the very large size and small resistances of the interconnected high-voltage system. Compared to the present 500 kV grid, the GIC level of the 1000 kV UHV network being planned and constructed can be expected to be higher.