Generalised modelling of power transformers in the harmonic domain

The periodic nonlinear behavior of a multilimb three-phase transformer is modeled in the harmonic domain, a frame of reference which allows cross-couplings between phases and between harmonics to be explicitly represented. The magnetic equivalent circuit is derived from the individual magnetizing characteristics of the core branches. The linearized transformer model, in the form of a harmonic Norton equivalent, is combined with the linear part of the electric network, and solved using a unified iterative procedure. The numerical solution involves a Newton-type iterative algorithm and a novel sparsity-oriented hybrid technique. Use of the proposed model in a practical transmission system has shown that the harmonic distortion caused by individual and multilimb core transformers is very different, with noticeable reduction in the multilimb case.>