Three phase $100$ $MVA$ ,$25$ $kV$ generator has solidly grounded neutral. The positive, negative, and the zero sequence reactances of the generator are $0.2$ $pu$, $0.2$ $pu$, and $0.05$ $pu$, respectively, at the machine base quantities. If a bolted single phase to ground fault occurs at the terminal of the unloaded generator, the fault current in amperes immediately after the fault is _________.