Response of power systems to the temporal characteristics of geomagnetic storms

Power lines are exposed to low frequency electromagnetic fields produced by natural (geomagnetic disturbance) sources. The resulting geomagnetically induced currents (GIC) produce excessive harmonics, which affect power system operations. The analysis presented makes extensive use of GIC data from different measuring sites in North American power grids and of geomagnetic data from different geomagnetic observatories. At low temporal resolution hourly GIC index shows good correlation with hourly geomagnetic index provided there is close proximity of the recorded sites. For higher resolution (one minute) the difference between time variations in GIC and geomagnetic field is significant. Although it has been widely popular to use time derivative of geomagnetic field as a characteristic of GIC, we show that ground conductivity is a critical parameter that needs to be included. This is especially important for sharp changes in geomagnetic field, for example, during the beginning of a geomagnetic storm (storm sudden commencement).