Harmonics and Switching Transients in the Presence of Geomagnetically-Induced Currents

Electrons and protons emitted by a solar flare can be caputured by the Earth´s magnetic field. The resulting transient in the geomagnetic field can produce quasi-dc currents in electric power systems. These geomagnetically-induced currents (GICs) cause half-cycle saturation in the transformers. GICs in excess of 100 amps have been measured in the transformer neutrals. With the practice of using EHV and UHV lines for transmitting ac power over long distances and because the systems are more solidly grounded, the problems posed by GICs have become more severe. This paper presents the effect of GICs on switching operations on long EHV transmission lines. Single pole switching and secondary arc currents, long line energization, out-of-step switching etc. are considered. The effect of harmonics caused by GICs is evaluated on the harmonic filter ratings of an adjacent HVDC terminal.