Power system harmonic analysis under geomagnetic disturbances

Geomagnetic disturbances influence the operation of transmission systems by injecting dc like electric currents into the system causing half cycle saturation of iron core magnetic circuits, generation of harmonic currents and excessive heating. Main harmonic generating devices are directly grounded transformers. The level of the half-cycle saturation depends of the level of geomagnetically induced currents and system parameters. GIC induced harmonics will flow to other devices in the system, depending on system topology and parameters and can influence system protection and operation. Accurate computation of these effects is of paramount importance. The paper proposes a high fidelity time domain modeling approach for analysis of the waveform distortion due to GIC and the propagation of the waveform distortion throughout the system. The high fidelity model incorporates the non-linear characteristics of iron core transformers, frequency dependent characteristics of transmission lines and grounding systems and other components of the power system. While GIC does not typically enters generator circuits by virtue of their grounding practice, generators are affected by GIC as harmonics propagate into generating units via the step up transformers.