Identify the formula for Surge Impedance Loading

The Surge Impedance Loading (SIL) of a transmission line is defined by the square of the line voltage divided by its surge impedance.

$SIL = \frac{V_L^2}{Z_c}$

Substitute given values

Given $V_L = 220 \text{ kV} = 220 \times 10°3 \text{ V}$ and $Z_c = 400$ $\Omega$.

$SIL = \frac{(220 \times 10°3)^2}{400}$

Calculate the result

Squaring the voltage gives $48400 \times 10°6$. Dividing by $400$ results in $121 \times 10°6 \text{ VA}$.

$SIL = \frac{48400 \times 10°6}{400} = 121 \times 10°6 \text{ VA} = 121 \text{ MVA}$