In a medium or ling transmission line when open-circuited or lightly loaded the receiving end voltage is found more than the sending-end voltage.
This phenomenon of rise in voltage at the receiving-end of the open-circuited or lightly or loaded line is called the ferranti effect owing to its first being observed on the depot ford mains laid down by S.Z. de Ferranti in 1890 .
The effect is due to voltage drop across the line inductance, due to charging current, being in phase with the applied voltage at the sending end of the line.
Thus both capacitance and inductance are necessary to causes phenomenon.
The capacitance, and therefore, charging current is negligible in short line but significant in medium and long transmission line .
On a 3000 km line operating on 50 hz supply, the receiving-end voltage on open circuit is usually found to be roughly 5% higher than the sending end voltage.