Modeling for transformer windings under VFTO based on s-parameters

To study the very fast transient over-voltage (VFTO) distribution in transformer windings in gas insulated substation (GIS), a systematic methodology based on s-parameters is presented for establishing high-frequency model of transformer windings in this paper. Firstly, voltage transfer functions are derived from s-parameters which are calculated or measured from transformer windings. Secondly, voltage transfer functions are fitted with rational functions by Vector Fitting method and then the rational transfer functions are order-reduced by optimal Pade-approximation algorithm. Lastly, the resultant voltage transfer functions are synthesized by network technology. Computational results are consistent with simulation results of Electromagnetic Transient Program (EMTP) to confirm the feasibility and validity of proposed methodology.