A 500-MVA 20-kV, 60-Hz synchronous generator with reactances Xá = 0.15, Xá = 0.24, Xd 1.1 per unit and time constants T'a = 0.035, T'a = 2.0, TA = 0.20s is connected to a circuit breaker. The generator is operating at 5% above rated voltage and at no-load when a bolted three-phase short circuit occurs on the load side of the breaker. The breaker interrupts the fault 3 cycles after fault inception. Determine (a) the sub-transient fault current in per-unit and kA rms; (b) maximum dc offset as a function of time; and (c) rms asymmetrical fault current, which the breaker interrupts, assuming maximum dc offset.
3 Cycle = "3 \\times" one cycle
"= 3\\times \\frac{1}{60}" sec
= 0.05 Sec
7 Cycle = 7"\\times" one cycle
"= 7\\times \\frac{1}{60}" sec
= 0.11667 sec
13 cycle = 13"\\times" one cycle
"= 13\\times \\frac{1}{60}" sec
=0,21667 sec
Comments
Draw the sequence networks for the circuit of Example 2.5 and calculate the sequence components of the line current. Assume that the generator neutral is grounded through an impedance Zn ¼ j10 W, and that the generator se- quence impedances are Zg0 ¼ j1 W, Zg1 ¼ j15 W, and Zg2 ¼ j3 W.
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