Specificity of Power Losses in Large Rectifier Transformers

Additional power losses in large rectifier transformers are caused by induced eddy currents in their windings' conductors and other conductive parts of these transformers. When designing these transformers, the calculation of additional power losses inside windings shall be paid more attention than the calculation of those of the ordinary transformer. The currents in the windings are not sinusoidal and contain a large amount of harmonics, e.g. odd harmonics (Table 1). The most troublesome are the 180 degrees phase-shifted harmonics (5, 7, 17, 19...) for causing a lot of additional power losses inside region A (Fig. 5). As seen from Eq. 3, the magnetic field distribution inside the transformer window needs to be calculated. The method (Fig. 3) appropriate for this task is the method of images. It enables a direct, simple and fast calculation of the magnetic flux density. The basic idea of the method is to remove ferromagnetic objects from the space of calculation in order to apply Eqs. 1 and 2. In that case the magnetic field can be calculated by superposition of magnetic fields of transformer windings and their images.