Models for capacitive effects in iron core transformers

The paper presents an efficient modeling technique for iron core coils and transformers based on a separation of the nonlinear inductive effects from the linear capacitive effects. The magnetic field is numerically analyzed neglecting the displacement currents. The distributed capacitive effects in the insulation between coils are concentrated in an “Extended II scheme,” an infinite circuit which is optimally reduced to a finite one. The separately extracted models are integrated in a common discrete (lumped) system. This global model obtained by postprocessing the numerical field solution was used to study the transmission of atmospheric lightning overvoltages to the secondary windings of power transformers