An approximate 2D method for computing the magnetizing zero-sequence impedances in 3-phase core-type transformers without tank

This paper describes an approximate 2D method for computing the magnetizing zero-sequence impedances in 3-phase core-type transformers without tank. These transformers do not have axial symmetry in their geometry, but a 2D model with axial symmetry is applied in order to obtain approximate results. The 3D models require more computational resources, and this fact justifies the search of an approximate method. The developed approximate method is based on the analysis of the main flux paths, and this method requires the application of approximation constants. These approximation constants are found by comparison between the results of 2D and 3D models, for units between 500kVA and 25 MVA. Experimental validation is included for one unit. The results indicate that the developed approximate method can be applied in order to compute these magnetizing zero-sequence impedances.