What is meant by Ferranti effect?

 an increasing the voltage at the receiving end of the long transmission line above the voltage at the sending end due to light loads , capacitive loads and no load.

at no load voltage at  recieving end in transmission line will more than sending end.

In long transmission line your receiving end voltage is more than sending end.

1. In case of light loading or no load operation of long transmission line , the receiving end voltage often increases beyond the sending end voltage, leading to a phenomena known as Ferranti Effect.

• Ferranti Effect is due to the rise in voltage at the receiving end than that of the sending end. This occurs when the load on the system reduces suddenly.
• Transmission line usually consists of line inductance, line to earth capacitance and resistance. Resistance can be neglected with respect to the line inductance. When the load on the system falls the energy stored in the capacitance gets discharged. The charging current causes inductive reactance voltage drop. This gets added vectorally to the sending end voltage and hence causes the voltage at the receiving end to raise
• A Long transmission line draws significant amount of charging current. If such line is open circuited or very lightly loaded at the receiving end, the voltage at the receiving end may become greater than sending end voltage. This effect is known Ferranti effect and is due to the voltage drop across the line inductance (due to charging current) being in phase with the sending end voltages. Therefore both capacitance and inductance is responsible to produce this phenomenon.
• The capacitance (charging current) is negligible in short lines, but significant in medium and long transmission line. Hence, this phenomenon is applicable for medium and long transmission line.The main impact of this phenomenon is on over voltage protection system, surge protection system, insulation level etc.