COMPARISON OF SS-GIC AND MHD-EMP-GIC EFFECTS ON POWER-SYSTEMS

A comparative study of the effects of solar storm geomagnetically indu ced currents (SS-GIC) and nuclear detonation geomagnetically induced c urrents (magnetohydrodynamic electromagnetic pulse GIC or MHD-EMP-GIC) on the power system. The earth surface electric field of the MHD elec tromagnetic pulse is given to be on the order of 100 V/km, with a dura tion up to several minutes; and the electric field of the solar storms is on the order of 10 V/km, and lasts from several minutes to one hou r. Both phenomena cause flow of almost direct current in the windings of power transformers through the grounding system. For long transmiss ion 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 eff ect on power system operation. The level of the transformer core satur ation depends on the time constant of the saturation process, and on t he duration and magnitude of the direct current through the transforme r windings. Thus, although the solar storm electric field is much lowe r than MHD-EMP, the solar storm effects on the power system are greate r due to their much longer duration. This paper presents a technique f or the computation of the induced and/or transferred voltages and curr ents to an electric power system from geomagnetic disturbances. For th is purpose, models of transmission lines which explicitly represent gr ounding, earth potential, and frequency dependent phenomena, and power transformers which explicit representation of nonlinear magnetization characteristics, are utilized.