What is the proximity effect? How to mitigate it?

Introduction:

Hey guys, you know that in alternating current, which is transmitted by transmission lines, there are many factors that affect this system. where there are skin effects, corona effects, proximity effects, etc. In this post, we will discuss the proximity effect, including what it is and why it exists. and how to reduce this phenomenon.

What is the proximity effect?

When a high-voltage alternating current flows through a conductor, this current can’t flow uniformly across the entire conductor surface. Not flowing an alternating current uniformly on a conductor surface is called the proximity effect.

Due to this effect, the apparent resistance of the conductor will increase. and losses will increase. This phenomenon was most common on transmission lines.

Passing two or more conductors near each other is the main reason behind the proximity effect.

Factors affecting the proximity effect:

Suppose that two or more conductors are passing nearby. When alternating current flows through these conductors, a magnetic field is generated due to the frequency. And we know that these conductors are almost there. So, these magnetic fields interact with each other’s magnetic fields.

Due to interaction, the flowing current density in the conductor will be different at every area of the conductor surface. It means that current will not flow uniformly across the entire surface of the conductor.

The direction of current flow determines which side of the conductor has the highest current density. And which side is the smallest? So, there are two conditions for flowing current in a conductor.

1. current flowing in the same direction
2. Current flowing in the opposite direction

What is the Ferranti effect and how to mitigate it?

When current flow is in the same direction:

Assume there are two conductors and that current flows in the same direction in both of them.

As a result, these two conductors’ half areas are close to each other. As a result, each half of the area has a cancelled magnetic field. And in this case, current will not flow in this area. So current will flow through the remaining half of these two conductors. which is a distant part of the conductors.

And thus, the current density is greater in the remote area of the conductors than in the nearby area of the conductors.

When the current is flowing in the opposite direction:

Now, if the current in the conductor is flowing in the opposite direction, The half-remote conductor areas then cancelled magnetic fields with each other. So remote parts will resist the flowing current, and nearby parts will have the maximum current density.

Factors affecting the proximity effect:

There are many factors that affect the proximity effect. like the conductor’s diameter, conductor material, conductor structure, and frequency, too.

Let’s discuss each one separately.

Conductor material:

As we have learned, the basic reason for this effect is a magnetic field. So, if we use a material that is ferromagnetic, then our magnetic field will increase. and the proximity effect will increase.

Conductor structure:

If we use a solid conductor, the proximity effect will increase. That’s why we use stranded conductors like ACSR (Aluminum Core Steel Reinforced) conductors in transmission lines. This conductor is made of many thin aluminum conductors and steel conductors.

Steel conductors reduce the surface area of the conductor, resultant this effect will decreased.

Conductor diameter:

If the diameter of the conductor increases, the proximity effect will increase.

Frequency:

If the frequency of the supply increases, the proximity effect will increase.

How to reduce the proximity effect in a transmission line:

To reduce this effect, we use an ACSR conductor. This ACSR conductor is not like a solid-type conductor. These conductors have become stranded. Steel wire is also reinforced in ACSR, which reduces the overall surface area. As a result, the proximity effect is reduced.