Impacts of Grounding Impedance on Second Harmonic Components Caused by GIC Flows in Power Transformers

Geomagnetic disturbances trigger quasi-dc currents that flow through grounding circuits into power systems, mostly through power transformers. Geomagnetically-induced currents (GICs) can cause severe harmonic distortions, disruption in reactive power flow, and/or thermal damage to power transformers. These adverse effects of GIC events on power transformers depend on the GIC magnitude, transformer core design, grounding circuit, and winding configuration. This paper analyzes the effects of grounding circuit designs on the adverse impacts of GIC flows in power transformers. These effects are analyzed through experimental tests carried out using laboratory 3ϕ, multicore power transformers. Experimental tests are performed for several grounding circuit designs for the test power transformers. Normal, magnetizing inrush, line-to-line, and line-to-neutral fault conditions are conducted for each tested grounding circuit design. Results of experimental tests show that grounding circuits with low impedance have minor effects on the GIC flows, while grounding circuits with high impedance tend to reduce the magnitude of the GIC. In addition, test results demonstrate that grounding circuits have little influence on the harmonic distortion (mainly the 2nd harmonic component) created by a GIC flow.