Short-Circuit Current Calculation for alternator

Isc= Ir/Xsc
Xsc= short circuit reactance

State              X"d                                X'd                                Xd
Xsc                10-20%                         15-25%                        200-350%


Example:
Alternator= 15 MVA
voltage = 10 kV
X'd= 20%

Ir= Sr/(sqrt(3) x voltage)
   =15/(1.732*10000) =870A

Isc= Ir/Xsc trans.
    = 870/(20/100) = 4350A = 4.35kA