Effects of recent geomagnetic storms on power systems

Significant geomagnetically induced currents (GIC) in power systems during the geomagnetic storms are the ground manifestations of the chain of events initiated by increased solar activity. Here we present the review of the largest geomagnetic storms, their solar sources and their associated GIC observed at the power grids. The geomagnetic activity was described by planetary Kp index and local hourly range index. Thus, we produce analogous GIC-indices, 3-hour and 1-hour, to compare them with geomagnetic indices. The results of comparison show relatively good correspondence of geomagnetic and GIC indices, better in case of local 1-hour indices. For more detailed investigations of GIC variations in time, however, the effects of ground conductivity need to be included. To show that, we compared GIC recordings with 1) rate-of-change of geomagnetic field as representation of the driving geo-electric field and 2) geo-electric field modeled by using 1-d approximation. It has been shown, that during sharp increases of the geomagnetic field, the effects of Earth conductivity are important to include in modeling; hence, modeled geo-electric field is better estimation of the GTC.