A RESEARCH ON HARMONIC MODEL OF THREE PHASE MULTI-LEGGED TRANSFORMER

A new harmonic modeling method for three phase multi-legged transformer based on its core topology is developed in which the three phase transformer is described by a set of electrical and magnetic circuit equations and three primary fluxes and magnetomotive forces (MMF) are used as the mediate variables to relate the electric circuit equations with magnetic circuit equations. The harmonic modeling problem of three phase multi-legged transformer is resolved into the analysis and calculation of the magnetizing currents of three phase transformer and the method for the analyzing and calculating the magnetizing currents in three phase transformers with three limbs and five limbs respectively is expounded. In the proposed model the saturation effect of transformer core is represented by monodromic magnetization curve. The eddy current and hysteresis losses in the core and the stray losses of the transformer are simulated by three equivalent resistances. Finally, the elementary procedure for establishing the harmonic models of three phase transformer in phase coordinate system is discussed.