Analysis of Three-Phase Transformer Response due to GIC Using an Advanced Duality-Based Model

In this paper, the behavior of three-phase transformers in the presence of geomagnetically induced current (GIC) is investigated. The associated phenomena involve very slow transients, in the millihertz range, while representing significant magnitudes of even and odd harmonics of power frequency. As a result, the transformer response involves nonlinear and frequency-dependent effects. This paper considers the impact of variations in the transformer core construction and design parameters on its saturated behavior and the resulting reactive power absorption, when subjected to GIC. A detailed transformer model is described including air-gap and tank effects. The study results highlight significant parameters that can affect transformer reactive power and promote them as being important parameters for GIC studies. Furthermore, the transformer dynamics during the slow transient of the GIC variations and polarity reversal are discussed.