Question

The ratings of a three-phase, three-winding transformer are Y connected, 66 kV, 20 MVA Primary (1): Secondary (2):Y connected, 13.2 kV, 15 MVA Tertiary (3): A connected, 2.3 kV, 5 MVA Neglecting winding resistances and exciting current, the per-unit leakage reactances are: X12 0.08 on a 20-MVA, 66-kV base X13 0.10 on a 20-MVA, 66-kV base X23 0.09 on a 15-MVA, 13.2-kV base (a) Determine the per-unit reactances Xi, X2, X3 of the equivalent circuit on a 20- MVA, 66-kV base at the primary terminals. (b) Purely resistive loads of 12 MW at 6-3 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 20-MVA, 66-kV base at the primary terminals.

Answer 1

Consider the following data: The ratings of a three phase y-connected transformer: primary winding, 66kv, 20 MVA Secondary winding, 2.3 KV, 5MVA The pre unit leaking recloses X_12 = 0.08 cm a 20-MVA, 66-KV base X_13 = 0.10 cm a 20-MVA, 66-KV base X_23 = 0.09 cm a 15 - MVA, 13 - 2 KV base a) The transformer is connected in three phase and also winding resistances and excitation current are Hence the transformer is considers as idea. The per unit leaking reactance of each winding is give respect to their Power delivered. The value of the X_12 and X_13 are d ready according to given base write the expression for per unit value of the reactive X_B for the given base value. X_23 = (base value taken/given base value) X_3 Where, the Per unit leakage reactance for base value of 20 MVA the per unit leakage reactance for base value of 15 MVA Substitute 0.09 for X_23 in the dove expression