pu = actual/base
rated phase consired at base value for alternator.
ohmic pu = ohmic actual/ohmic base
pu = ohmic actual*current base/voltage base
Consider all above phase values
MVA (3phase) = 3 Vph Iph
Iph = 500*10⁶/(3*28901.73) = 5766.66 A
pu = ohmic actual*current base/voltage base
0.5 = ohmic actual*5766.66/28901.73
ohmic actual = 2.5 Ω