Enhancements to Terminal Duality-based models for three-phase multi-limb multi-winding transformers

This paper introduces an enhanced electromagnetic transient (EMT) model for three-phase multi-limb multi-winding transformers based on the Terminal Duality Method (TDM). The proposed model improves accuracy by incorporating zero-sequence path inductances, specifically for three-limb transformers, which are formulated for the first time. A closed-form formula is developed to precisely calculate the zero-sequence path inductance, ensuring that the transformer’s open-circuit zero-sequence impedance aligns with the user-provided value. Additionally, the inductances of the yoke sections beneath the winding stacks are considered by distributing the yoke inductances across each winding. Furthermore, a stabilization technique is implemented for nonlinear inductive cutsets by introducing a reference node to represent the tank voltage. The proposed model is implemented in RSCAD-RTDS and validated through extensive simulations and comparative studies, demonstrating its effectiveness and accuracy.