Simulation analysis of geomagnetically-induced currents (GIC) effects on shell-form transformers

Transformer DC excitation due to geomagnetically-induced currents was studied by 3D analysis based on an in-application 280 MVA 500kV/230kV single phase auto transformer design. As a result of previous studies, the transformer design studied here incorporated non-magnetic stainless steel to limit local heating. Coil and surrounding metal structure temperatures were observed to determine the limits imposed by the design at 25%, 50%, 75%, and 100% load conditions. GIC levels studied here were 10A/phase, 50A/phase, 100A/phase, 200A/phase, and 400A/phase. The results demonstrated that the maximum safe coil temperature was 118.0 deg. C with a GIC condition of 200A/phase. The maximum surrounding metal structure temperature was 110.4 deg. C during a GIC event of 400A/phase. The analysis´ conclusion shows that a design of this nature can withstand GIC conditions up to 200A/phase at 100% load and up to 400A/phase at 100% load for a short period of time lasting a few minutes.