On the Transformer Core Dynamic Behavior During Electromagnetic Transients

This paper introduces the concepts of 1) dynamic inductance and 2) effective inductance based on the magnetic energy, and provides a new insight on the transformer core behavior during steady-state and transient regimes. Based on a newly developed core modeling approach, which is described in references one to four, this paper also: 1) addresses the intrinsic limitations of the single-valued magnetization characteristic-based core model; 2) uses the dynamic inductance as the key parameter to fully and accurately represent the core behavior; and 3) explains the reason for discrepancies among the reported core behavior based on the simulated and experimental results. In contrast to the widely accepted belief that a single-valued magnetization characteristic-based model can accurately represent the transformer core behavior, this paper demonstrates the necessity of a dynamic and physically correct hysteresis core representation. This paper also compares various core representations in terms of their accuracies for the ferroresonance simulation. This paper shows that: 1) the single-valued core model not only cannot accurately represent the core behavior under asymmetric excitation conditions, it may provide erroneous results even under symmetric excitation conditions and 2) the accuracy of specific transients highly depends on the precise representation of the hysteresis minor loops and the core dynamic inductance.