Question

A 200-MVA, 345-kV/34.4-kV Y substation transformer has an 8% leakage reactance. The transformer acts as a connecting link between a 345-kV transformer and a 34.4 kV distribution. Transformer winding resistance and exciting current are neglected. The high-voltage bus connected to the transformer is assumed to be an ideal 345-kV positive sequence source with negligible source impedance. Using the transformer ratings as base values, determine the per-unit magnitude of transformer voltage drop and voltage at the low-voltage terminals when rated transformer current at 0.8 PF lagging enters the high voltage terminals. Also, determine the per-unit magnitude of the fault current when a three-phase-to-ground bolted short circuit occurs at the low-voltage terminals.

          A 200-MVA, 345-kV/34.4-kV Y substation transformer has an 8% leakage reactance. The transformer acts as a connecting link between a 345-kV transformer and a 34.4 kV distribution. Transformer winding resistance and exciting current are neglected. The high-voltage bus connected to the transformer is assumed to be an ideal 345-kV positive sequence source with negligible source impedance. Using the transformer ratings as base values, determine the per-unit magnitude of transformer voltage drop and voltage at the low-voltage terminals when rated transformer current at 0.8 PF lagging enters the high voltage terminals. Also, determine the per-unit magnitude of the fault current when a three-phase-to-ground bolted short circuit occurs at the low-voltage terminals.

Added by Renee H.

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