Ferranti Effect - An Overview

Ferranti effect refers to the phenomenon in transmission lines when the receiving end voltage is higher than the sending end voltage.

A long transmission line draws two types of currents.  One is the current drawn by the load at the receiving 
end.  Another current is the current drawn by the line capacitance.

If a long transmission line is lightly loaded, the charging current of the capacitance can be more than the actual load current.  The voltage drop caused by the charging curent of the capacitance gets added to the 

sending end voltage and causes the receiving end voltage to be higher than the sending end voltage.  

Hence, a transmission line should not be loaded below its surge impedance loading value.

The Ferranti Effect can be compensated by adding series capacitors to compensate for the series inductances and shunt inductances to compensate for shunt inductances.  

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