Numerical calculations of three-phase transformer´s transients

A three-phase, two-winding transformer´s model is presented in the paper. The triplex core configuration is assumed in the transformer´s model. Nonlinear magnetizing curves are piecewise linearized. Input winding capacitances can be lumped to the transformer´s terminals. A stiff differential system in state space, describing transformer´s transient behavior, is solved by the L-stable backward differentiation formulas numerical rule. BDF compared to trapezoidal rule shows better stability properties. A computer program is developed for generation of variable state waveforms. The developed program is suitable for simulations of low-frequency three-phase transformer transients such as inrush currents and ferroresonance. Results of the developed program are compared to MATLAB/power system blockset results.