GIC immune transformers - An evaluation of their GIC elimination and fault behaviour

Abstract: Geomagnetically Induced Currents (GICs) arise from fluctuations in Earths magnetic field and can reach alarmingly high levels and cause malfunctions or blackouts in the power grids in which they occur. AF Klercker Alaküla and Lindahl invented a patented GIC immune transformer which eliminates the effects of GICs, though it is not known how this implementation will affect the transformers behavior during un-symmetrical faults. This project aims to clarify the impact of the patented implementation, with regard to fault current and voltage rise at single-line-to-ground faults, as well as verify the beneficial effects on GICs. Experiments on lab transformers corresponding to the specifications in the mentioned patent and simulations of a full scale equivalent were performed. Both the experiment and simulation results show that the GIC immune transformer eliminates the effects of GIC. The simulations also indicate that the fault current, of a bolted single-line-to-ground fault, is increased, and the voltages decreased, by replacing a regular transformer with the patented implementation. For unaltered current and voltages a grounding reactance can be used. The work shows that such a reactance should be the sum of the uncompensated grounding reactance and one third of the transformers uncompensated zero-sequence reactance.