Question

Four alternators of similar rating 5 MVA, 132 kV with 16% of reactance on its own base are connected in parallel to a bus bar. The value of short-circuit level in MVA of the bus bar will be

• A. 50 MVA
• B. 100 MVA
• C. 125 MVA
• D. 150 MVA

Answer 1

The correct option is C 125 MVA

For given power system four alternators are connected in parallel,



Thevenin's impedance, $Z_{th}=\frac{0.16}{4}=0.04$ pu

Also, fault current in pu, $I_f=\frac{1}{Z_{th}}=\frac{1}{0.04}=25pu$

per unit short-circuit of system,

$MV{A}_{sc}=25$ pu
$\therefore$ short-circuit MVA, $MV{A}_{sc}=25\times baseMVA$
$=25\times 5=125$ MVA