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.

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 $$\Omega $$.

Three sections of a feeder are provided with circuit breakers CB1, CB2, CB3, CB4, CB5 and CB6. For a fault F as indicated in figure.

A rectangular current pulse of duration T and magnitude 1 has the Laplace transform