Repeat Problems 9.1 and 9.14 including \(\Delta-Y\) transformer phase shifts. Assume American standard phase shift. Also calculate the sequence components and phase components of the contribution to the fault current from generator \(n\) ( \(n=1,2\), or 3 as specified by the instructor in Problem 9.2).

Problem 9.1

The single-line diagram of a three-phase power system is shown in Figure 9.17. Equipment ratings are given as follows:

Synchronous generators:

Transformers:

Transmission lines:

The inductor connected to Generator 3 neutral has a reactance of 0.05 per unit using generator 3 ratings as a base. Draw the zero-, positive-, and negative-sequence reactance diagrams using a \(1000-\mathrm{MVA}, 765-\mathrm{kV}\) base in the zone of line 1-2. Neglect the \(\Delta-Y\) transformer phase shifts.

Problem 9.14

Determine the subtransient fault current in per-unit and in kA, as well as the per-unit line-to-ground voltages at the fault bus for a bolted single line-to-ground fault at the fault bus selected in Problem 9.2.

Problem 9.2

Faults at bus \(n\) in Problem 9.1 are of interest (the instructor selects \(n=1\), 2, or 3). Determine the Thévenin equivalent of each sequence network as viewed from the fault bus. Prefault voltage is 1.0 per unit. Prefault load currents and \(\Delta-Y\) transformer phase shifts are neglected. 

G1 1000 MVA G2 1000 MVA G3 500 MVA G4 750 MVA 15 kV 15 kV 13.8 kV 13.8 kV X = X = 0.18, X, = 0.07 per unit X = X = 0.20, X, = 0.10 per unit X = X = 0.15, X, = 0.05 per unit X = 0.30, X = 0.40, X, 0.10 per unit =