Case Studies of 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 one of the common paths for GIC flows into power systems. The flow of GICs through a power transformer can create adverse impacts on its operation, including disruptions in the reactive power flow and significant harmonic distortions in primary and secondary side currents. This paper presents case studies for analyzing the harmonic distortion in primary and secondary side currents due to various levels of GIC flows in power transformers. Presented case studies are conducted on two laboratory power transformers with different core types, power ratings, voltage ratings, and winding configurations. Each of these power transformers is tested for various levels of GIC flows with its loading being varied from no-load to rated power. Results of conducted case studies conclude that the dc component, $2^{\mathrm{n}\mathrm{d}}$ harmonic, and $3^{\mathrm{r}\mathrm{d}}$ harmonic are dominant in primary and secondary sides currents at all levels of GIC flows. Other harmonic components ($5^{\mathrm{t}\mathrm{h}}, 6^{\mathrm{t}\mathrm{h}}$, and $7^{\mathrm{t}\mathrm{h}}$) can be observed with lower magnitudes than the dc component, $2^{\mathrm{n}\mathrm{d}}$ harmonic, and $3^{\mathrm{r}\mathrm{d}}$ harmonic.