The effect of geomagnetic disturbances on the electric grid and appropriate mitigation strategies

Geomagnetic induced currents (GICs) generated by space weather, such as solar storms, currently pose a threat to North American electric grids. GICs enter the power grid through the neutral connection of high voltage transformers causing unusual megawatt and megavar flows, voltage fluctuation, frequency shifts, undesired relay operations, high third harmonic currents, and telemetry and supervisory alarm failures in the power grid. A storm on the order of 5000 nT/min is believed to occur in the not too distant future. Once this storm occurs, widespread damage to the power grid of unprecedented proportions will take place. Mitigation strategies must be considered. Systems involved in restoration and reinstitution of the power grid need to be prioritized, and the effectiveness of existing black-start procedures need to be evaluated. This paper explores the effects of GICs on high voltage power transformers and presents a 37-bus critical infrastructure case. In the event of a geomagnetic disturbance, it is not plausible to protect all the high voltage transformers in the power grid, but by protecting critical transformers, and bypassing others, the grid´s integrity can be maintained.