New power transformer model for the calculation of electromagnetic resonant transient phenomena including frequency-dependent losses

A new power transformer model for the accurate predetermination of transient resonant processes is introduced in this paper. The accurate representation of the losses is the most important feature of the new model, since it has been developed for the accurate determination of maximal stresses during resonance phenomena within transformers. The new equivalent circuit only contains constant lumped parameters. It represents very accurately the frequency variation of all impedances (real and imaginary parts) of the transformer, including mutual magnetic coupling. This allows carrying out transient calculations in the time domain directly using programs for the electromagnetic transients calculations like EMTP. Several laboratory measurements on transformer winding models have been performed in order to verify the agreement of measured and calculated values of resonant overvoltages.