Effects of Iron-Core Topology on Inrush Currents in Three-Phase Multi-Leg Power Transformers

This paper investigates the inrush currents of three-phase (a)symmetric multi-leg transformer cores considering magnetic core structure (e.g., three-leg vs. five-leg) and switching effects (e.g., recloser operating). The electromagnetic steady-state and transient behavior of three-phase transformers significantly differs from single-phase transformer operation mainly because of the unique flux coupling interactions in multi-leg and asymmetric core structures. A recently developed three-leg nonlinear transformer core model is applied to this study which considers the influence of magnetic hysteresis, flux couplings in the core-structure and nonsinusoidal operation in three-phase transformers. Simulations results for multi-leg (e.g., three-leg and five-leg) transformer cores demonstrating inrush current behavior based on the model are presented and discussed.