$9\mathrm{.}56$ The system shown in Figure $9\mathrm{.}28$ is the same as in Problem $9\mathrm{.}48$ except that the transformers are now Y$-$Y connected and solidly grounded on both sides. $($a$)$ Determine the bus impedance matrix for each of the three sequence networks. $($b$)$ Assume the system to be operating at nominal system voltage without prefault currents, when a bolted single$-$line$-$to$-$ground fault occurs on phase A at bus $3.$ Compute the fault current, the current out of phase C of machine $2$ during the fault, and the line$-$to$-$ground voltages at the terminals of machine $2$ during the fault.

FIGURE $9\mathrm{.}28$

Problem $9\mathrm{.}56$