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The principal mechanism for producing geomagnetically induced currents (GICs) in electric power systems is the induced earth-surface-potential (ESP) due to geomagnetic field fluctuations during a geomagnetic storm. The ESP, which can be 3-6 V/km or higher during severe storms, is impressed across the grounded neutral points of three phase transformers. The ESP acts essentially as a voltage source that has a frequency in the range of a few millihertz. The GIC biases the excitation characteristics of transformers causing half-cycle saturation. The saturation result in a highly distorted exciting current rich in harmonics and drastically increases reactive power consumption in transformers. The large reactive power losses that occur simultaneously are sufficient to cause dangerous or even intolerable system voltage depression. The injected harmonics also create relay problems. The transformer itself can be severely stressed and repeated exposure can even ultimately lead to transformer failure. Generator heating and relay failures are also often observed at times of geomagnetic storms.
GICs have been recorded by the power industry during many years. The first documented case, occurred on Easter Sunday, March 24, 1940. On the US East coast many disturbances were noted on March 24, such as reactive power disturbances and misoperating relays. A severe geomagnetic storm was the cause and the Ap index reached 207. The most spectacular solar-terrestrial event took place in March 1989. The entire province of Quebec experienced a blackout lasting more than nine hours. The Hydro-Quebec power company lost more than 21 500 MW. A large generator step-up transformer at a nuclear plant on the US east coast was damaged. Also in Sweden many effects were noted. Seven 130 kV-lines tripped. Fire alarms went on. Large fluctuations in the power transmission were noted.
The Swedish power company Sydkraft measured a 5 degrees increase in temperature of a rotor in a nuclear plant on March 13, 1989.
ELFORSK, ABB and NUTEK have created an electrical power engineering R&D program called ELEKTRA.
Space weather effects on power systems is a project in the ELEKTRA program. The objective of the program is to create and to cross analyze data bases with solar-terrestrial events, and geomagnetically induced current (GIC) effects recorded by the power industry. Develop a model for prediction of GIC effects due to geomagnetic storms in order to make possible for the power industry to better withstand the effects and accomplish a stable and safe transmission of power.
Geomagnetic Storms and Impacts on Power Systems by John G. Kappenman.
Geomagnetically induced currents - Hazard for power systems, pipelines etc., by Ari Viljanen (FMI/Finland)
