Identify Total MVA

Since there are 4 alternators in parallel, each rated at 5 MVA, the total capacity is $4 \times 5 = 20 \text{ MVA}$.

$MVA_{total} = 4 \times 5 = 20 \text{ MVA}$

Determine Per Unit Reactance

The reactance given is 20%, which in per-unit (p.u.) form is 0.20.

$X_{pu} = \frac{20}{100} = 0.2$

Calculate Short Circuit Level

Using the formula for short circuit capacity, divide the total MVA by the per-unit reactance.

$MVA_{sc} = \frac{20}{0.2} = 100 \text{ MVA}$