Analysis of the Effects Caused by Structural Asymmetries in the Performance of Three-Limb Core Three-Phase Inductive Filters

A considerable number of nonlinear industrial loads employ three-phase inductive filters to reduce their peak currents and mitigate the conduction of harmonic currents into the supply system. In modeling and analysis of this kind of filter, the fact that-for reasons of economy-they consist of a single block where the three electrical phases share the same magnetic core instead of having three single-phase reactors is often overlooked. Since the three windings are coiled in the same plane, the central magnetic limb of the core has a lower magnetic reluctance than do the lateral limbs. Moreover, this undesired effect is increased by the existence of internal magnetic couplings. The above phenomenon, which might, at first sight, be considered negligible, will become noticeable in real electrical facilities because of the particular operating conditions of three-phase inductive filters. The aim of this paper is, thus, to present a new model for three-limb core three-phase inductive filters that includes all the above parasitic effects and to describe its practical application in order to assess the magnitude of the errors produced by traditional models when estimating real filter behavior.