Three single-phase, two-winding transformers, each reated 450 MVA, 20 kV/288.7 kV with leakage reactance Xeq=0.12 per unit, are connected to form a three-phase bank. The high voltage windings are connected in Y with solidly grounded neutral. Draw the per-unit zero, negative, and positive sequence networks if the low-voltage windings are connected:
A) in delta with American standard phase-shift
B) in Y with an open neutral
C) in Y with grounded neutral. Use the transformer ratings as the base quantites. Winding resistance and excitation current are negligible.