For the power system given in Problem 7.14, a three-phase short circuit occurs at bus 4 , where the prefault voltage is \(138 \mathrm{kV}\). Prefault load current is neglected. Determine

(a) the Thévenin equivalent at the fault,

(b) the subtransient fault current in per unit and in kA rms, and

(c) contributions to the fault from transformer T2 and from line 3-4.

Problem 7.14

Equipment ratings for the five-bus power system shown in Figure 7.15 are as follows:

A three-phase short circuit occurs at bus 5, where the prefault voltage is 15kV.

Generator Gl: Generator G2: Transformer Tl: Transformer T2: Each 138-kV line: 50 MVA, 12 kV, X" = 0.2 per unit 100 MVA, 15 kV, X"= 0.2 per unit 50 MVA, 10 kV Y/138 kV Y, X = 0.10 per unit 100 MVA, 15 kV A/138 kV Y, X = 0.10 per unit X = 40 2.