Comparison of SS-GIC and MHD-EMP-GIC effects on power systems

A comparative study of the effects of solar storm geomagnetically induced currents (SS-GIC) and nuclear detonation geomagnetically induced currents (magnetohydrodynamic electromagnetic pulse GIC or MHD-EMP-GIC) on the power system. The earth surface electric field of the MHD electromagnetic pulse is given to be of the order of 100 V/km, with a duration up to several minutes; and the electric field of the solar storms is of the order of 10 V/km, and lasts from several minutes to one hour. Both phenomena cause flow of almost direct current in the windings of power transformers through the grounding system. For long transmission lines, i.e. 300 miles or longer, this DC current offsets the 60 Hz AC and may saturate transformer cores, with secondary results such as high magnetization currents, increased harmonics, and concomitant effect on power system operation. The level of the transformer core saturation depends on the time constant of the saturation process, and on the duration and magnitude of the direct current through the transformer windings. Thus, although the solar storm electric field is much lower than MHD-EMP, the solar storm effects on the power system are greater due to their much longer duration. This paper presents a technique for the computation of the induced and/or transferred voltages and currents to an electric power system from geomagnetic disturbances. For this purpose, models of transmission lines which explicitly represent grounding, earth potential, and frequency dependent phenomena, and power transformers which explicitly represent nonlinear magnetization characteristics, are utilized