What is the Ferranti effect and how to mitigate it?


Hey, guys, you’re aware that many phenomena occur in an alternating-current transmission line. where there is the skin effect, proximity effect, corona loss, and Ferranti effect, among others. Now in this post, we will discuss the Ferranti effect. What is the Ferranti effect, what is the root cause of it, and how can we mitigate it?

What is the Ferranti effect?

Definition: When receiving voltage is greater than sending voltage in a transmission line, this is called the Ferranti effect.

What is the Ferranti effect

In general, we know that when we transfer power from one location to another in this process, there is a slight voltage drop at the receiving end. It is because of the power loss in the cable or conductor used in this process. And in transmission lines, we use very long transmission conductors to transmit power. And when we increase conductor length, the loss will increase as well.

Voltage drop due to loss

But what is the factor in the transmission line that causes the voltage to rise at the receiving end?

What is the cause of the Ferranti effect?

If we want to tell someone in just one line, we can say it is because of an imaginary capacitor in the transmission line.

However, if someone asks, “What is an imaginary capacitor?”

Then we have to know: What is an imaginary capacitor?

Essentially, when we transmit power, we use three-phase wires. and the transmission voltage is very high. like in kilovolts. and the conductor are both the same distance apart. As a result of the high voltage, the air between the conductors becomes charged. Consequently, air works as a dielectric material. And thus, the whole set of circumstances creates an imaginary capacitor.

And we know that an imaginary capacitor reduces the current in line. As the current in the line is reduced, the loss decreases, and as a result, the voltage level rises.

How can we reduce the Ferranti effect?

If you think that increasing the voltage value is good for our transmission line, you are wrong. because our substations run on a proper voltage rating.

Suppose that a substation’s rating is 132 kV/33 kV. And 132 kV of power is supplied by a distant power generation station. It means that our power at the generation station is 132 kV, but due to the Ferranti effect, at the substation (132 kV/33 kV), it becomes 134 kV, which is high. But at our substation, our transformer rating is 132 kV/33 kV, a step-down transformer. Now this transformer gets 134 kV instead of 132 kV. So, due to the high voltage, the transformer can get burned.

So, we have to reduce this overvoltage. To solve this problem, we use a shunt reactor at a substation. The shunt reactor basically compensates for the reduced current and regulates the voltage level. And then it provides the supply to the transformer.

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