Identify given parameters

The base capacity is given as $S_{base} = 100\ MVA$ and the percentage impedance $Z_{pu}$ is $10\% = 0.1$.

$S_{base} = 100\ MVA, \ Z_{pu} = 0.1$

Apply fault level formula

The fault level (Short Circuit MVA) is calculated by dividing the base capacity by the per unit impedance.

$S_{fault} = \frac{S_{base}}{Z_{pu}}$

Calculate the result

Substituting the values into the formula gives $S_{fault} = 100 / 0.1 = 1000\ MVA$.

$S_{fault} = \frac{100}{0.1} = 1000\ MVA$