Impacts of Loading Level on Harmonic Distortion in 3ϕ Auto-Transformers During GIC Flows

Geomagnetically induced currents (GICs) are quasi-dc currents that flow through grounding circuits into power systems. These currents are triggered by geomagnetic disturbance events, and flow into power systems through grounded, power system components, including 3ϕ auto-transformers. A GIC flow through a 3ϕ auto-transformer can lead to high levels of harmonic distortion in currents, overheating of auto-transformer windings, and significant increase in auto-transformer reactive power demands. The severity of GIC flow impacts on a 3ϕ auto-transformer can be dependent on the core design, winding configuration, grounding circuit, and GIC current. This paper discusses possible contributions of loading levels to GIC impacts on a 3ϕ auto-transformer. These possible contributions are analyzed through experimental tests carried out using a laboratory 3ϕ, multi-core auto-transformer. Experimental tests are conducted for various GIC flows, where the loading level is varied. Test results conclude that the loading level of a 3ϕ auto-transformer can influence the harmonic distortion created by a GIC flow. In addition, test results show that loading level and load power factor have influences on the reactive power demands of a 3ϕ auto-transformer, when experiencing a GIC flow.