12-1. A 200 MVA, 20 kV, 60 Hz, three-phase synchronous generator is connected through a 200 MVA, 20/138 kV, Δ-Y transformer to a 138 kV transmission line. The generator reactances to the machine’s own base are
| Xs = 1.40 | X′ = 0.30 | X″ = 0.15 |
The initial transient dc component in this machine averages 50 percent of the initial symmetrical ac component. The transformer’s series reactance is 0.10 pu, and the resistance of both the generator and the transformer may be ignored. Assume that a symmetrical three-phase fault occurs on the 138 kV transmission line near to the point where it is the transformer.
(a) What is the ac component of current in this generator the instant after the fault occurs?
(b) What is the total current (ac plus dc) flowing in the generator right after the fault occurs?
(c) What is the transient fault current I′f in this fault?
(d) What is the steady-state fault current If in this fault?
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