Transformers of high frequency resistance spot welding systems are considered. The equivalent circuit of a three-winding transformer, which is obtained by replacing it with two two-winding transformers, is used. It is shown that the magnetic coupling factor for the leakage fluxes of these two-winding transformers influences on the output current. The study of the transformers includes both 2D eddy-current FEA analysis for estimation the leakage impedance and the circuit simulation, which gives the output current. The results are used to design economical welding transformers. The calculation results are confirmed experimentally. Streszczenie. Zaprojektowano transformator do wsokoczestotliwościowego punktowego zgrzewania. Przeprowadzono analizę rozkładu prądów wiroychw celu uwzględnienia impedancji upływowej oraz zaproponowano schemat zastępczy transformatora trzy-uzwojeniowego otrzymanego przez zastąpienie dwóch transformatorów dwu-uzwojeniowych. Modelowanie wysokoęstotliwościowego transform,atora do rezystancyjnego zgrzewania

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3D model for calculating the short circuit impedance and inductance of the secondary windings bars of a welding transformer are given. An example of calculating these parameters for a transformer with a rated current of 7 kA in the frequency range from 0 up to 1000 Hz are considered. The accuracy of these parameters and calculation time are discussed. The results of transformer impedance calculations using 2D and 3D models are compared. The inductance of the transformer bars is about 70% of the transformer short-circuit resistance.