The impact of nonlinear loads on anisotropic transformers is investigated. The saturation of the iron-core materials, the anisotropy of the with- and cross-grain laminations, the dependency of the iron-core losses on the amplitudes of the fundamental and harmonics of the flux density and the dependency of the iron-core losses on the waveshape (harmonic phase shifts) of the flux density are included in this analysis. The impact of nonlinear loads on anisotropic transformers exhibits itself as an increase in losses (%) and consequently a decrease in the performance or derating of the transformer. The approach to obtain the increases in losses (%) requires the computation of the appropriate input voltage and the core-loss resistances assuming that the fundamental components of the output voltage and current have rated quantities and that the secondary current contains a certain amount of low-order harmonics, caused by the nonlinear loads. The determination of derating factors of transformers requires a three-step iterative method assuming rated fundamental output voltage and rated secondary apparent power while maintaining rated losses.
