Calculation of short circuit impedance and leakage impedance in transformer windings

A method for calculating short-circuit and leakage impedances in transformer windings is described. The method is based on a formula which is derived from an exact solution of Maxwell´s equations for coils on ferromagnetic cores. The calculation is based on winding geometry and on the core magnetic permeability and effective electrical resistivity. Eddy-current losses in the core and windings are included. The model takes account of the frequency-dependent nature of short circuit and leakage impedances in transformers. Results are presented for a ferrite pot core of the type used in switching mode power supplies