What is the Ferranti effect experienced on a long overhead transmission line when it is?

The Ferranti effect occurs primarily in long transmission lines under lightly loaded conditions. This phenomenon results from the line's capacitance, which becomes significant compared to its impedance when the load is reduced. In lightly loaded scenarios, the capacitive reactance of the transmission line can lead to a situation where the receiving end voltage is higher than the sending end voltage.

As the load decreases, the capacitive charging of the line increases, causing the voltage to rise at the receiving end due to the line's inherent capacitance. This is particularly noticeable in long overhead lines, where the inductive and capacitive elements are more pronounced.

In contrast, when transmission lines are heavily loaded or overloaded, the voltage drop caused by the line's inductive reactance predominates, typically resulting in lower receiving end voltages. Similarly, under short-circuit conditions, the dynamics differ because the system's impedance drastically reduces, causing a significant reduction in voltage. Thus, the Ferranti effect is specific to the lightly loaded state of the transmission line, making this scenario the correct answer.