Design of dc-bias resilient transformers

Geomagnetic disturbances (GMDs) give rise to geomagnetically induced currents (GICs) on the earth’s surface which find their way into power systems via grounded transformer neutrals. The quasi-dc nature of the GICs results in half-cycle saturation of the power grid transformers which in turn results in transformer failure, life reduction, and other adverse effects. Therefore, transformers need to be more resilient to dc excitation. This paper sets forth dc-bias immunity metrics for single- and three-phase transformers. Furthermore, this work sets forth novel transformer architectures and a design methodologies which employ the dc immunity metrics to make transformers more resilient to dc-bias excitation. The results are demonstrated using a time-stepping 2D finite element analysis (FEA) simulation. It is shown that a relatively small change in the core geometry significantly increases transformer resiliency with respect to dc excitation.