The positive-sequence Zaus matrix of the system shown in Figure 1, without considering the radial system involving T3 and bus 7, is the following: Z_{B U S}:=Y_{B U S}{ }^{-1}

The elements of the matrix are in per unit, using 345kV in the 345kV lines and 100 MVA as the basis. \text { The line impedances in ohms/mile, neglecting the resistance is: } \bar{z}_{L}=0.65 j \Omega / \mathrm{mi} The lines' lengths are: L1=80miles; L2=40 miles; L3=60 miles; L4-90 miles; L5-40 miles; L6-50 miles a) Calculate the three-phase fault current (in amps) for a perfectly balanced three-phase fault at bus 6 assuming the pre-fault voltage at the faulted bus to be 1 per unit and neglecting all loads. b) Calculate the voltage (in per unit) at bus 1 during the fault described in a. (2p) c) Calculate the current (in amps) flowing from bus 4 to bus 6 during the fault described in a. In this part, do not invert Zaus. (2p) d) Calculate the current (in amps) flowing from bus 5 to bus 6 during the fault described in a. In-this part, do not invert Zaus. (2p) e) Without modifying the Zaus matrix, calculate the fault current for a balanced three-phase fault atbus 7 (2p).