A 3-PHASE 3-WINDING CORE-TYPE TRANSFORMER MODEL FOR LOW-FREQUENCY TRANSIENT STUDIES

A topology-based and duality-derived three-phase, three-winding, core- type transformer model is presented. The model treats the leakage indu ctances and the coupling effects of the core in a straightforward and integrated way The long-established positive- and zero-sequence star e quivalent circuits of a three-phase three-winding transformer are deri ved from the original equivalent magnetic circuit of the transformer b y applying duality. Formulations for determining the values of the lea kage inductances and the core loss resistances from transformer open- and short-circuit test data are presented. A supporting routine is wri tten to generate the lambda-i curves for each segment of the core and the other input data for EMTP. Since the duality-derived model consist s of only RLC elements, no device-specific code to EMTP time-step code is needed. Winding capacitances are lumped to the terminals. The mode l is suitable for simulation of power system low-frequency transients such as inrush currents and ferroresonance, short circuits, and abnorm alities including transformer winding faults.