Chapter 7, Problem 7.12P

Equipment ratings for the four-bus power system shown in Figure 7.14 are as follows:

Generator G1: 500 MVA, 13.8 kV, $X"=0.20$ per unit

Generator G2: 750 MVA, 18 kV, $X"=0.18$ per unit

Generator G3: 1000 MVA, 20 kV, $X"=0.17$ per unit

Transformer T1: 500 MVA, $13.8\Delta /500\text{Y}\text{kV},X=0.12$ per unit

Transformer T2: 750 MVA, $18\Delta /500\text{Y}\text{kV,}X=0.10$ per unit

Transformer T3: 1000 MVA, $20\Delta /500\text{Y}\text{kV,}X=0.10$ per unit

A three-phase short circuit occurs at bus 1, where the prefault voltage is 525 kV. Prefault load current is neglected. Draw the positive-sequence reactance diagram in per unit on a 1000-MVA, 20-kV base in the zone of generator G3. Determine (a) the Thévenin reactance in per unit at the fault, (b) the subtransient fault current in per unit and in kA rms, and (c) contributions to the fault current from generator G1 and from line 1-2.