What effect does having a line loaded below its SIL have on the line voltage?

When a line is loaded below its Surge Impedance Level (SIL), it behaves in a capacitive manner. The SIL represents the load level at which the reactive power generated by the line matches the reactive power consumed, allowing for optimal voltage stability. When the actual load is less than this level, the line tends to exhibit capacitive characteristics, which means that it can generate reactive power.

This generation of reactive power contributes to a rise in the line voltage because the capacitive nature counteracts some of the inductive reactance typically present in transmission lines. As a result, the voltage on the line increases when it is loaded below its SIL, creating higher voltage levels compared to the nominal voltage.

Therefore, the correct understanding of the behavior of transmission lines below their SIL is that it creates a more capacitive situation leading to an increase in the line voltage, aligning perfectly with the option that indicates the line becomes more capacitive and the voltage raises.