Investigating Harmonic Distortion in Power Transformers Due to Geomagnetically Induced Current Flows

Geomagnetically induced currents (GICs) flow through grounding circuits into power systems, when triggered by geomagnetic disturbances. Power transformers (with grounding connections) are the primary path for GIC flows into power systems. The flow of GICs through a power transformer can create adverse impacts on its operation, including large increases in its reactive power demands and significant harmonic distortions in the primary side currents. This article presents case studies and analyses of the adverse impacts of GIC flows on power transformers. Presented case studies are conducted on two power transformers with different core types, power ratings, and voltage ratings. Each of these power transformers is tested for various levels of GIC flows with its loading being kept unchanged. Results of conducted case studies conclude that the $\text{2}$ nd harmonic is the dominant in primary and side currents at all levels of GIC flows. Other harmonic components such as the $\text{3}$ rd, $\text{4}$ th, $ \text{5th},\ \text{6th},\ \text{7th}\ \text{and}\ \text{8}$ th harmonic components, can be observed with lower magnitudes than the $\text{2}$ nd harmonic component.