Computation of Wide Band Network Parameters and Macromodeling of Transformer Windings

The suppression and protection of over-voltage in power system, as well as the study of electromagnetic compatibility in power system need to build electromagnetic transient model of the components and equipments. In these components and equipments, the transformers [including power transformers, PT/CT, reactor, etc.] with complex structure as well as frequency-dependent effects in high-frequency, are the most difficult to model. The transient modeling for the equipments based on the "black box" approach is necessary to get the network functions of the equipments by measuring. In order to overcome the problem that the wide band network functions of the large-scale equipments of transformer\´s type are difficult to measure, this paper presents a macromodeling method to obtain the wide band network functions of the transformer windings through calculation by means of the finite element method and then establish its circuit model based on the "black box" technique. First, the multi-conductor transmission line model of the transformer windings is established; and then by adopting the finite element method, the per-unit-length parameter matrices of the transmission line are calculated; the two-port admittance parameter matrix of high-voltage transformer windings side to each section is deduced, based on the telegraph equations and boundary conditions; On this basis, a two-port ¿-equivalent circuit model of the transformer windings is established. The comparison of time-domain simulation and measured results verifies the feasibility and effectiveness of the demonstrated method.