The influence of geomagnetically induced currents (GIC) on transmission systems

Charged particles emitted by the sun from flares or similar phenomena can enter the magnetic field of the earth and induce large currents within the earth. These currents follow a circular path around the magnetic poles and are large enough to produce earth surface potentials up to 10 volts per mile. Such currents have been known to last for many minutes, effectively a dc mode which can saturate power or current transformers. Factors known to influence susceptibility to the phenomenon include grounding philosophy, transformer core construction, transmission line length and orientation, and local geology. In this paper plans for a mitigation scheme and a warning network are explained