High-frequency EMTP model of transformer windings

An EMTP model is presented for calculating overvoltage in transformer windings under VFTO in this paper. Firstly, the voltage transfer functions are calculated from the S parameters which are measured by network analyzer or calculated from the distributed parameters of transformer windings. Secondly, the voltage transfer functions are fitted with rational functions by vector fitting codes and then the rational transfer functions are order-reduced by Fade approximation. Lastly, the resultant voltage transfer functions are synthesized by the elements in EMTP. The calculated voltages from the circuit by EMTP are in good agreement with the measured voltages. This shows that the method is simple and robust.