Impacts of Transformer Loading on the Harmonic Distortion Created by GIC Flows

Geomagnetically induced currents (GICs) are currents dominated by dc components that flow through grounding circuits into power systems. These currents are typically initiated by geomagnetic disturbances, and flow into power systems through power transformers with grounded windings. The flow of a GIC through a power transformer creates adverse impacts, including high levels of harmonic distortion in the currents flowing through the grounded windings, overheating of transformer windings, and significant disruptions in the reactive power flow through the affected transformer. Adverse impacts of GICs on power transformers depend on various factors, among which are the core design (multi-cores, 3-limb, or 5-limb), configuration of primary and secondary windings, and loading levels. This article presents and discusses the effects of loading levels on the harmonic distortion due to GIC flows in power transformers. Tests are carried out using a laboratory power transformer with multi-core (three single phase transformers). Various values of GIC flows are tested for different loading levels. Test results conclude that the loading levels have minor ifluence on the harmonic distortion created by the GIC flow. In addition, test results show that the
$2{\text{nd}}$
harmonic component remains the dominant harmonic component due to the GIC flow in a power transformer, regardless of the loading level.