An Improved Wide Frequency Model for VFTO of Power Transformers Using Transfer Functions

An accurate understanding of power transformer high frequency behavior is very important to assess the impacts on power system due to transient over-voltage conditions. An improved method of modeling power transformer under very fast transient over-voltage conditions (VFTO) is presented in this paper that provides a convenient way of obtaining winding and core responses of power transformers using existing circuit synthesis method. End-to-end short circuit and open circuit sweep frequency response analysis data are converted into transfer functions using a novel algorithm based on Levy and Sanathanan-Koerner methods, that are used in the development of lumped circuit model later. These transformer models can be implemented in a transient analysis software and can be used in power system analyzing under VFTO with greater accuracy.