A star connected synchronous generator rated at 500 MVA, 50 kV has a reactance of 0.5 pu. Find the ohmic value of the reactance.

• A. 1 Ω
• B. 0.1 Ω
• C. 0.25 Ω
• D. 2.5 Ω

Answer: (D)

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