Why are shunt reactors used at the terminals of long EHV lines?

Shunt reactors are utilized at the terminals of long Extra High Voltage (EHV) lines primarily to stabilize line voltage against capacitive charging currents. When long transmission lines are energized, they exhibit capacitive characteristics, particularly at higher voltage levels. This capacitive behavior can lead to an increase in voltage along the line, especially when it is lightly loaded or unloaded.

By installing shunt reactors, the capacitive reactive power that is introduced by the line is effectively counteracted. The shunt reactor absorbs reactive power, thus providing a means to balance the voltages and maintain stability in the electrical system. This helps prevent voltage rises that could potentially exceed acceptable limits, which could lead to insulation failure, equipment malfunctions, and overall instability in the power system.

In contrast to the other options, enhancing power factor efficiency and preventing overload conditions do not specifically address the challenges posed by capacitive effects under the conditions present in long EHV lines. Improving current flow during light loading is not the primary function of a shunt reactor, as its main role is to manage reactive power, not to enhance the flow of current itself.