[en] A one-dimensional model of an aircore transformer is developed through which it is possible to analyze the effect of eddy currents in the primary windings--and of similar currents in the field coils for the toroidal magnetic field--on the time dependence of the current in a Tokamak experiment. The model is applied to the Alcator Tokamak, and its accuracy is tested by comparing analytical results for the harmonic behavior of the transformer, with experimental data. The time dependent behavior of the plasma current--for a constant plasma resistance--shows that eddy currents in the primary windings will lead to a reduction of 8% of the current maximum. The eddy currents in the Bitter coils are found to affect predominantly the initial current rise, they lead to a steepening of the current rise. Finally, the influence of the time dependence of the plasma resistance is investigated