Transformer inrush calculations using a coupled electromagnetic model

The paper describes a method, using time domain analysis, in which the equations of mixed electrical and magnetic systems are solved not as separate but as a single system. The advantages of this method, from the viewpoint of a power system designer, are discussed and the inrush current is calculated for typical 5 kVA and 180 MVA transformers. From a transformer designer´s viewpoint the distribution of fluxes within the transformer becomes more apparent so that the analysis of inrush and its implications can be carried out at the design stage. It is also shown how different parts of the transformer can be saturated to differing levels and how this can be incorporated into the analysis