Effects of geomagnetically-induced currents in power transformers from power systems point of view

Geomagnetically-induced currents (GICs), passing through the grounded neutral leads of power transformers, produce simultaneous AC-DC excitations causing some degree of half-cycle transformer saturation which may cause a number of associated problems. A quantitative evaluation of produced harmonics, VAr demand, copper loss, and iron loss of the transformer under GIC is presented. The impact of these effects depends on the ratio of GIC to the critical GIC necessary to cause full transformer saturation. Theoretical results are supported by digital simulation results using the Electro-Magnetic Transients Program (EMTP).