Evaluating the amplitude of the transformer magnetizing inrush currents caused by geomagnetic disturbances

The paper presents a mathematical model of the magnetizing branch of a shell-form transformer. This model helps derive analytical expressions reflecting instantaneous values of the magnetizing current caused by geomagnetic disturbances, and a qualitative criterion for the magnetic system saturation depth under the effect of geoinduced currents. Also, the paper presents the relationship between the transformer magnetic system saturation depth and the geoinduced current intensity, with respect to the actual magnetic switching right before the occurrence of geomagnetic disturbances. The paper presents derived qualitative estimations of magnetizing inrush currents caused by geomagnetic disturbances (magnitude of such currents may be 2.8 to 7.15 higher than the nominal current of high-voltage windings of a transformer, reaching short-circuit current values).