Accounting for the Influence of the Tank Walls in the Zero-Sequence Topological Model of a Three-Phase, Three-Limb Transformer

A method is proposed to account for the influence of the tank walls in the topological transient model of a three-phase, three-limb core-type transformer. The influence of the transformer tank walls as a distributed-parameter hysteretic element is reproduced by solving a diffusion equation that describes the penetration of the plane electromagnetic wave into the depth of the wall. The reliability of the model is validated by comparing its zero-sequence impedances to those measured on a 25-MVA transformer, in the presence and absence of a tertiary stabilizing winding. An Electromagnetic Transients Program-Alternate Transients Program implementation of the model is outlined.