Abstract
White-box detailed transformer models are used by manufacturers for predicting internal overvoltages in transformer windings during the lightning impulse test. One such model is the d-factor model which is based on a lumped-parameter description based on winding discretization with inclusion of losses via an empirical, frequency-dependent damping factor. This paper shows a procedure for direct inclusion of the d-factor model in electromagnetic transients simulation programs for use in general studies of network overvoltages. Proper utilization of the model's diagonal structure is utilized in combination with real-valued arithmetic for maximum speed in transient simulations, with optional initialization from sinusoidal steady state conditions. The model can be used both as a terminal equivalent and for calculation of internal voltages with use of an augmented input data set. The method is demonstrated for a single-phase three-winding transformer which is applied in a simulation study of transient resonant voltage buildup in the tertiary winding.