8. Three 6.6 kV, 12 MVA, 3-phase alternators are connected to a common bus bars. Each...

8. Three 6.6 kV, 12 MVA, 3-phase alternators are connected to a common bus bars. Each has reactance to positive sequence current of 15%. The reactance to negative and zero sequence current are 75% and 30% of the positive sequence value. If an earth fault occurs on one of bus bar, determine the fault current when one of the alternator neutral is earthed through a resistance of 0.25 ohm and the others are isolated.

9. Four identical alternators each rated for 20 MVA, 11 kV have a subtransient reactance of 16% are working in parallel. The short circuit level at the bus bar is.

10. A generator having a solidly grounded neutral and arte 50-MVA, 30 kV has positive, negative and zero sequence reactances of 25, 15 and 5 percent respectively. What reactance must be placed in the generator neutral to limit the fault current for a line to ground fault to that for a three phase fault?

Solutions

Expert Solution

Note: When the reactances are given in per unit it will be easier to solve in per unit and in last test base value is multiplied accordingly .

: Remember the standard fault formulae in p.u. to avoid calculations .

Manojponduru answered 4 months ago

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