On the Interaction of Power Transformers and Geomagnetically Induced Currents

Geomagnetically induced currents (GIC) cause partial saturation of transformers leading to a variety of power system effects. Extensive work has been done to model the transformer response to GIC; however, little consideration has been given to how transformer inductance affects the growth of GIC. Here, we present a new method based on calculating the effective inductance of the transformer experienced by GIC. A step-by-step method is used to calculate each step in the growth of GIC, the fraction of time in saturation, and the effective inductance. The new value of effective inductance is then used to calculate the next step in GIC. Model results for a dc step voltage are in agreement with previously published detailed modelling and show the nonlinear response of transformers. The new technique provides a versatile and fast method for modelling the transformer interaction with GIC and provides a way of assessing the GIC frequencies that need to be considered in assessment of the geomagnetic hazard to a power system.