[ V_pu = \fracV_actualV_base, \quad I_pu = \fracI_actualI_base, \quad Z_pu = \fracZ_actualZ_base ] where ( Z_base = \fracV_base^2S_base ), ( I_base = \fracS_base\sqrt3 V_base ) (three-phase system). For a three-phase fault at a bus, the fault current magnitude is:
( Z_Tx = 0.08 , \textpu ) (already on 10 MVA base). fault current calculation
( I_f = 1.0 / 0.09 = 11.11 , \textpu )
[ I_f = \fracV_thZ_th ] where ( V_th ) is the prefault voltage at the fault point (usually 1.0 pu), and ( Z_th ) is the Thevenin equivalent impedance seen from the fault point (resistance + reactance). In high-voltage systems, resistance is often neglected, giving: In high-voltage systems
( S_base = 10 , \textMVA ), ( V_base, HV = 115 , \textkV ), ( V_base, LV = 13.8 , \textkV ). resistance is often neglected