Hysteresis curves of a resistance spot welding transformer

Purpose - The aim of the paper is to provide a simple and reliable hysteresis model for prediction of magnetization curves of a resistance spot welding transformer (RSWT) core, operating in a wide range of flux densities and excitation frequencies. Design/methodology/approach - The hysteresis model considered in the paper is the T(x) description advanced by J. Takacs. Three options to extend the model to the dynamic magnetization conditions are considered. The excitation conditions differ from those prescribed by international standards. Findings - The quasi-static Takacs model combined with a fractional viscosity equation similar to that proposed by S.E. Zirka outperforms other considered options. The effect of eddy currents may be considered as a disturbance factor to the frequency-independent quasi-static hysteresis loop. Research limitations/implications - The combined approach yields in most cases a satisfactory agreement between theory and experiment. For highest frequency considered in the paper (1 kHz) excessive "heels" were observed in the modelled loops. This artifact may be reduced by the introduction of a more complicated relationship for the viscous term. Future work shall be devoted to this issue. Practical implications - The combined Takacs-Zirka model is a useful tool for prediction of magnetization curves of a RSWT core in a wide range of flux densities and excitation frequencies. Originality/value - The usefulness of the Takacs description has been verified in a practical application. The model is able to predict magnetization curves under non-standard excitation conditions.