A high frequency circuit model for current transformer based on the scattering parameter

For an accurate simulation of the electromagnetic interference from primary system to the secondary system caused by transients through potential and current transformer (PT/CT) in the substation, a high frequency circuit model for PT/CT is of vital importance. In this paper a new method to setup high frequency circuit model for CT is proposed. First, the two ports scattering parameter of the CT are transformed in to the Y-parameter and the admittances of the equivalent "Pi" circuit. can be computed. Second, the Vector Fitting method is used to fitting the admittances by rational functions using real poles as well as conjugate poles. At last, a circuit synthesis method is applying to build the circuit model of the CT. Time domain simulation result agrees with measurement results thus the validation of the method proposed in this paper has been proved.