Calculation of harmonic loss in converter transformer tank shells based on the impedance boundary condition

In order to investigate the applicability of impedance boundary condition for the harmonic loss analysis in converter transformer, the harmonic loss of the model of coil and aluminum plate structure was analyzed using this method, and the results were compared with those from the traditional finite element method (FEM). Compared with the traditional FEM which requires the mesh of both coils and internal medium, the impedance boundary condition does not have to mesh the internal medium, which means a smaller grid number. The calculation result from the impedance boundary condition is in consistent with that from the traditional FEM. However, the former method needs less time to calculate and demands lower computer performance. In addition, the internal magnetic field and harmonic loss of a three-phase converter transformer are obtained based on the impedance boundary condition. The results show that the material properties and working conditions in three-phase converter transformer are in accordance with the assumption of semi-infinite conductor. The first assumption is that the length of conductor which contains electromagnetic wave is much less than the wavelength outside the conductor, the second is that the length of the conductor is much larger than wavelength inside the conductor. The two assumptions are matched when the losses of transformer are analyzed from 50 Hz to 2450 Hz. The harmonic loss of the three-phase converter transformer can be calculated by using the impedance boundary condition, which indicates that the method is suitable for large-scale harmonic converter transformer loss simulation.