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Overvoltages and dielectric stresses caused by transient conditions can result in the failure of transformer windings. Adequate prediction of these conditions is generally based on the implementation of accurate computer models, which, in turn, require an accurate computation of electrical parameters. This paper analyzes the computation of frequency-dependent core and proximity losses included in the transient model of transformer windings, using the finite element method and analytical expressions. A modified formula to calculate the proximity losses is presented. The results from a frequency-domain winding model are compared with experimental measurements on a disk-type prototype winding. These results show that including the frequency-dependent proximity losses is essential to accurately reproducing the experimental results. They also show that the core losses have a modest effect on the transient response of the winding when compared with measurements. [ABSTRACT FROM AUTHOR]