A High Frequency Strictly Passive Model for Transformer Based on the Image Method under Lightning Overvoltage

Abstract

In the power system electromagnetic transient simulation, the establishment of a stable power transformer simulation model is crucial. Therefore, the high frequency strictly passive model of the transformer is investigated, which is suitable for the lightning strokes. The proposed model is introduced based on two-port network theory where its scattering parameters are measured through network analyzer firstly, and then the scattering parameters are transformed into the impedance parameters, finally the transformer T-equivalent circuit is established. The image method is used to fit frequency dependent impedance parameter, and according to different types of the parameter, the combination of circuit elements R, L, C is needed. By using the image method the values of the elements achieved are all positive and the strictly passive conditions of the circuits are guaranteed. Furthermore, the experiment and simulation results of a 10kV single-phase transformer under lightning overvoltage is presented, confirming the validity of the proposed method.