A transmission line that is loaded above its surge impedance loading (SIL) acts as what?

When a transmission line is loaded above its surge impedance loading (SIL), it behaves as a net user of reactive power. The surge impedance loading is the power level at which the reactive power demand of the line is perfectly balanced by the reactive power generated. When the load exceeds this level, the line absorbs reactive power from the system, effectively acting as a net user of reactive power.

This behavior can be understood in terms of how transmission lines operate. At loads below SIL, the line can provide reactive power support to the connected load. However, once the load exceeds this threshold, the line's inductive characteristics dominate, and it starts to draw reactive power from the connected system to compensate for the excess load.

This principle is essential for understanding power factor and reactive power management in electric systems, especially in transmission networks. By recognizing this relationship, operators can better manage voltage stability and reactive power flows within the grid.