$1.$ A $3-$phase short circuit occurs in an $11$ kV network at a distance of $7$ km from the

substation. The feeder resistance and reactance are r $=0\mathrm{.}247/$km$,$ x $=0\mathrm{.}102/$km$.$ The

total resistance and reactance of the supplying network are Xs $=2$ and Rs $=0\mathrm{.}1.$

a$)$ Calculate the fault current at the end of the cable.

b$)$ Calculate the voltage on the substation busbar during the fault.