Full-wave modeling of potential transformers for the very fast transient simulation under high-frequency base on balanced truncation

The wide frequency circuit models of potential and current transformers (PT/CT) is indispensable in accurately simulating the electromagnetic interference from primary system to the secondary system caused by the very fast transient over-voltages through instrument transformers in gas-insulated substation. This paper presents a systematic methodology for establishing the high-frequency (0.1 MHz to 10 MHz) circuit model of PTs based on the balanced truncation (BT). Firstly, the two-port scattering parameters of the PT are transformed into the Y parameters, then, the vector-fitting code is used to approximate the admittances of the equivalent circuit model by rational functions consisting of real as well as complex conjugate poles and residues. Secondly, balanced truncation for model order reduction is used to Y parameters. At last, full-wave circuit synthesis method is applied to build the circuit model. The proposed method is general and robust. The simulation and measurement results are presented, confirming the validity of the proposed model.