A modeling for transformer windings under Very Fast Transient Over-voltages

To investigate the Very Fast Transient Over-voltage (VFTO) distribution in transformer windings in Gas Insulated Substation (GIS), a systematic methodology based on hybrid model is presented for establishing high-frequency model of transformer windings in this paper. Firstly, the voltages at the end of each coil are calculated by means of Single-Conductor Transmission Line Model (STLM). Secondly, according to these values, over-voltages distribution along the turns is determined on the basis of Multi-Conductor Transmission Line Model (MTLM). Lastly, an actual autotransformer windings model which is provided by Baoding Tianwei Group is studied, calculated results shows that this algorithm significantly reduces the number of linear equations that needed to be solved for each frequency to determine the required voltages in frequency domain, and the computational results are consistent with Electromagnetic Transient Program (EMTP) to confirm the feasibility and validity of proposed methodology.