Question

A three-phase short-circuit fault occurs at point F. in the system shown in figure below. The fault current is _____________A.

• A. 878.5

Answer 1

The correct option is A 878.5
Let, base MVA = 30 MVA and let 33 kV be the base voltage
$X_{G1}=\frac{30}{20}\times 0.15=0.225p.u.$
$X_{G2}=\frac{30}{10}\times 0.10=0.30p.u.$

$X_{trans}=\frac{30}{30}\times 0.05=0.05p.u.$
$Z_{line}=(3+j15)\times \frac{30}{{33}^2}=(0.0826+j0.4132)p.u.$



$Z_{total}=0.0826+j0.5918$
$=0.5975\angle {82}^{\circ }p.u,$

$SCMVA=\frac{30}{0.5975}=50.21MVA$
$SCcurrent=\frac{50.21\times {10}^6}{\sqrt{3}\times 33\times {10}^3}=878.5A$