The ratings of a three-phase three-winding transformer

Chapter , Problem 3.51

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The ratings of a three-phase three-winding transformer are: Primary (1): Y connected, 66 kV, 15 MVA Secondary (2): Y connected, 13.2 kV, 10 MVA Tertiary (3): D connected, 2.3 kV, 5 MVA Neglecting winding resistances and exciting current, the per-unit leakage reactances are: X12 = 0:08 on a 15-MVA; 66-kV base X13 = 0:10 on a 15-MVA; 66-kV base X23 = 0:09 on a 10-MVA; 13:2-kV base (a) Determine the per-unit reactances X1, X2, X3 of the equivalent circuit on a 15-MVA, 66-kV base at the primary terminals. (b) Purely resistive loads of 7.5 MW at 13.2 kV and 5 MW at 2.3 kV are connected to the secondary and tertiary sides of the transformer, respectively. Draw the per-unit impedance diagram, showing the per-unit impedances on a 15-MVA, 66-kV base at the primary terminals.