The Research On Establishing Method Of The Broadband Nonlinear Model For Power Transformer

As an important electrical equipment in the electric power system, it is important to ensure the power transformer’s safe operation and its stability. Some of the transformer parameters not only obtain the nonlinear characteristics, but also are frequency dependent.For different simulation requirements, different transformer models are used during the research of transformer modeling, few models can simulate the response of power transformer under the power frequency, low frequency and high frequency transient situations. Therefore, the research of the power transformer broadband nonlinear model has both theoretical significance and practical application.This paper studies the method of establishing the broadband nonlinear model of the power transformer, and based on the Epstein frame to establish its broadband nonlinear circuit simulation model using the method in this paper.Firstly, the methods of establishing low- and mid-frequency model and high frequency model are introduced, then the transformer broadband nonlinear model is proposed and the Epstein frame and its characteristics are introduced.Secondly, the method of transformer broadband nonlinear model is obtained, and the broadband nonlinear model can be divided into linear module and nonlinear module. The admittance parameters are obtained by the scattering parameter measurement method, the modified vector fitting is used to fit the admittance parameters and the circuit parameters of the linear module are obtained by the circuit synthesis.The frequency dependent impedance of iron core is derived, the modified vector fitting is used to fit the expression to obtain the parameters of each branch of the iron core frequency dependent circuit. For the nonlinear characteristics, the inductance is treated as a nonlinear inductance in order to establish the nonlinear module of the broadband model.Finally, the Epstein frame is modeled. In order to verify the model, the experiments of the power frequency steady state, lightning overvoltage and very fast transient overvoltage are conducted to compared with the simulation results, the results verify the validity of the broadband nonlinear model.