Empirical representation of transformer branch impedance frequency dependency

High-frequency transformer models for use in system transient studies should include the transformer’s frequency-dependent effects to give reliable simulation results. The most accurate white-box modeling approach is based on the branch impedance matrix Z b with inclusion of frequency-dependent effects, in combination with the capacitance matrix. The required calculation of Z b at many time frequency samples using FEM can be very time consuming, due to the large dimension of Z b . We show that the frequency dependency in Z b can be approximately taken into account by an empirical frequency response that is derived from an eigenvalue of Z b from a representative transformer. That way, the long computation time by FEM is avoided. The proposed method is demonstrated to be more accurate than usage of the classical Fergestad’s damping factor method.