The Ferranti effect is a phenomenon in long AC transmission lines where the voltage at the receiving end is higher than the voltage at the sending end. This counterintuitive voltage rise occurs when the line is either operating at no-load or a very light load. It is a critical factor to manage, as the overvoltage can damage equipment and compromise system stability.

The effect is most prominent in long-distance, high-voltage lines and is a direct result of the line's inherent shunt capacitance and series inductance.