A High Frequency Two-port Circuit Model for Potential Transformer Based on the Scattering Parameter

For accurate simulation of voltage stress on secondary circuits caused by very fast transient over-voltage in gas insulated substation (GIS), a sophisticated modeling of potential and current transformers (PT/CT) is of vital importance. A new method is proposed to setup high frequency two-port circuit model of PT based on scattering parameters. First, the scattering parameters of PT are transformed in to Y-parameters and equivalent "π" circuit model could be established. Second, vector fitting method is used to approximate admittances of equivalent "π" circuit model by rational functions. At last, a circuit synthesis method for rational functions is applied to build circuit model. The simulation and measurement results are presented, which confirmed validity of the proposed model. The proposed method is effective and general, and overcomes the limitation of former methods. The model setup by this method can make simulation more accurate of conductive coupling through PT/CT in GIS.