For the configuration shown in figure, the breaker connecting a large system to bus $$2$$ is initially open. The system $$3$$-phase fault level at bus $$3$$ under this condition is not known. After closing the system breaker, the $$3$$-phase fault level at bus $$1$$ was found to be $$5.0$$ p.u. What will be the new $$3$$-phase fault level at system bus $$3,$$ after the interconnection? All per unit values are on common base. Prefault load currents are neglected and prefault voltages are assumed to be $$1.0$$ p.u. at all buses.

Determine the required MVA rating of the circuit breaker CB for the system shown in given figure. Consider the grid as infinite bus. Choose 6 MVA as base. Transformer 3-phase, 33/11 kV, 6 MVA, 0.01+j0.08 p.u. impedance. Load 3-phase 11 kV, 5800 kVA, 0.8 lag, j0.2 p.u. impedance. Impedance of each feeder 9+j 18 $$\Omega $$.

Determine the magnitudes of the symmetrical components ($${{{\rm I}_{R1}},\,{{\rm I}_{R2}}\,}$$ and $${{{\rm I}_{R0}}}$$) of the currents in a three phase (RYB) three wire system, when a short circuit occurs between R and Y phase wires, the fault current being 100 A.

In a power-system, the $$3$$-phase fault MVA is always higher than the single-line-ground fault MVA at a bus (State True or False)