What is Ferranti Effect in Transmission (causes & disadvantage)

In the Power System of Electrical Engineering, when the receiving end voltage in an AC transmission line is greater than the sending end input voltage, it is called as Ferranti effect. Remember, it only dominates in a Long transmission line whose length is greater than 200 Km. Also, this effect occurs more effectively when the load is very small or no load.

A transmission line has two major parameter if it is a long or medium type. Such parameters are Line inductance and Line Capacitance. Also there is the influence of line resistance but it is very less as compared to both of them. Only these two Line capacitance and Line inductance are the rivals of the ferranti effect.

The above mentioned two parameters needs charging and discharging. So they take charging current and discharge that stored power to the transmission line as load. Ferranti effect is due to the charging current of the line. when AC is applied to the inductor/ inductor it take current and this is called as charging current or capacitive current.

Causes of Ferranti Effect

The influence of the Line capacitance and line inductance is the major elements increasing the Ferranti effect. Additionally, the line should have very less load or no load. Ferranti effect occurs more in the short underground cable lines because it has a larger capacitance per unit length value.

CausesLine Inductance, Line Capacitance.
Loadvery small load or No load conditions
Other effectsskin effect, corona effect etc.

Disadvantage or problems

As this effect increases the receiving end voltage, the load damages. Because every load can’t handle higher voltage values.

As we have seen various problems are due to this effect. So to protect our systems we need to reduce these problems by using the below techniques.

How to reduce this effect

We need compensators to overcome this effect.

  • A combination of the capacitors and Inductors in series and a shunt as a Compensator is added to the transmission line to reduce this effect.
  • So we place shunt reactors at the receiving end of the transmission line to overcome Capacitive current (VARs).

Thus this can compensate for this effect up to the prescribed limits.

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