Transformer design with consideration of restrained inrush current

Numerous factors that affect the design of transformers have been considered, including steady-state characteristics, volume, capacity, and others. The transient characteristics or inrush current that can cause the inadvertent operation of the protective system has not been evaluated. This paper proposes a novel approach for transformer design with an altered winding coil distribution to restrain the inrush current. The approach can provide the high inrush equivalent inductance and the suitable leakage inductance for a transformer. In order to estimate a satisfactory distributive ratio for the atypical winding configuration before manufacture, the inrush equivalent inductance and the leakage inductance are derived from the structural parameters of the transformer. During the study period, 220 V/110–220 V 5 kV A transformers were developed as demonstrations. The proposed method is verified by theory, in simulated results and field tests, not only is the inrush current constrained, but also the appropriate leakage inductance are retained.