The one-line diagram of a simple 4-bus power system is shown in the figure below Each generator is represented by an emf behind the transient reactance. All of the impedances are expressed in per unit on a common MVA base. All resistances and shunt capacitances are neglected. The generators are operating on no load at their rated voltage with their emfs in phase. A bolted three-phase fault occurs at bus 4. 9.30.20 j0.20 j0.15 j0.20 j0.20 j0.50 1 2 j0.20 j0.30 j0.19 (a) A bolted three-phase fault occurs at bus 4. Using the bus impedance matrix cal- culate the fault current, bus voltages, and line currents during fault. (b) Repeat (a) for a three-phase fault at bus 2 with a fault impedance of Z = j0.0225.