Computation of very fast transient over-voltages (VFTO) in transformer windings

A new method to calculate very fast transient over-voltages (VFTOs) in transformer windings has been presented. The applied algorithm uses a hybrid model which is a combination of the multi-conductor transmission line model (MTLM) and the single-transmission line model (STLM). The voltages at the end of each coil are calculated with the STLM model. Then, these values are used in the MTLM to determine the distributed over-voltages along the turns. Several representative curves with respect to time in transformer windings are illustrated. The maximums of over-voltage and electric field intensity generated in wire coils and in wire turns are also given. It is essential for transformer´s insulation design.