Understanding the Ferranti Effect

In long transmission lines under no-load or light-load conditions, the charging current (due to shunt capacitance) flowing through the line inductance causes a voltage rise at the receiving end, known as the Ferranti effect.

$V_r > V_s$

Identifying the Problem

Because $V_r > V_s$ at no load, the voltage profile is poor. To maintain a constant voltage profile, we need to compensate for this excess capacitive reactive power.

$Q_{cap} = V² \times \omega C$

Applying Compensation

A shunt reactor at the receiving end provides inductive reactive power ($Q_{ind}$) which neutralizes the leading capacitive reactive power ($Q_{cap}$) generated by the line capacitance, thereby reducing the receiving end voltage.

$Q_{ind} + Q_{cap} \approx 0$