Impact of nonlinear loads on anisotropic transformers

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 of the flux density are included. The impact of nonlinear loads on anisotropic transformers exhibits itself as an increase in losses (%). The approach for obtaining the increase 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 related losses