A 25-MVA, three-phase, 13.8-kV, two-pole, 60-Hz Y-connected synchronous generator was tested by the open-circuit test, and its air-gap line was extrapolated with the following results (L-L = line-to-line voltage):
Field current, A
320 365 380 475 570
Open-circuit voltage, kV (L-L)
13.0 13.8 14.1 15.2 16.0
Air-gap line, kV (L-L)
15.4 17.5 18.3 22.8 27.4
Assume that the curves are linear between data points. The armature resistance is 0.24 Ω/phase and the leakage reactance is 1 Ω/phase. For a terminal voltage of 13.8 kV with a load of 20 MW.