The Research On The Modeling Method Of Passive And High Frequency Circuit Model For Potential Transformers In GIS

In order to study the interference caused by Very Fast Transient over-voltage(VFTO) generated by switching operations to the secondary circuits via potential/current transformers (PT/CT) in GIS, a high frequency circuit model is setup based on black-box technique in this paper. The Y parameters is transformed from the S parameters of PT and approximated by rational functions using the Vector Fitting at first. In order to improve the simulation stability of circuit model, a correction to the rational function of admittance matrix of PT is calculated, which enforces the circuit model is input-output passive. At last, two kinds of circuit model composed of RLC are synthesized. The simulation and measurement examples of a transformer winding and 10kV PT are presented, confirming the validity of the proposed model. The proposed method is effective and general which provides a powerful tool for researching the interference caused by VFTO to the secondary circuits.