8. Three 6.6 kV, 12 MVA, 3-phase alternators are connected to acommon bus bars. Each has reactance to positive sequence current of15%. The reactance to negative and zero sequence current are 75%and 30% of the positive sequence value. If an earth fault occurs onone of bus bar, determine the fault current when one of thealternator neutral is earthed through a resistance of 0.25 ohm andthe others are isolated.
9. Four identical alternators each rated for 20 MVA, 11 kV havea subtransient reactance of 16% are working in parallel. The shortcircuit level at the bus bar is.
10. A generator having a solidly grounded neutral and arte50-MVA, 30 kV has positive, negative and zero sequence reactancesof 25, 15 and 5 percent respectively. What reactance must be placedin the generator neutral to limit the fault current for a line toground fault to that for a three phase fault?
