Why do they split the phase in EHV transmission lines?

Hello dear subscribers and guests of my channel! Today I want to tell you why on extra-high voltage (EHV) lines, the phase wire is split into two, four and eight wires, respectively. So let's get started.

What are EHV lines

So, to begin with, I will say a few words about what SVL Lines are and why they are so important. So, the EHV lines include lines that operate under a voltage of 330 kV, 500 kV, 750 kV and 1150 kV, respectively.

They are also called backbone, and the totality forms nothing more than a single energy system of our country with you, and also provides energy communication with the systems of neighboring countries.

These lines are needed primarily in order to transmit high power and at the same time minimize losses (which are inversely related to the voltage value).

This means that the failure of such a line is a significant blow to the energy system of the entire country.

Therefore, special requirements are imposed on the reliability of such lines. And one of the design solutions, which is designed to ensure maximum reliability and solve a number of serious problems, is splitting the phase wire into several wires.

Why split the phase

Structurally split phase is a construction of several separate wires, which are oriented in space so that the wires are placed at the vertices of regular polygons.

How many wires you need to split one phase is determined using special calculations. In order not to bore you with formulas, I will say that at the moment the EHV phases are split as follows:

1. At a voltage of 330 kV, each phase has two wires.
2. At a voltage of 500 kV, there are 3 wires in each phase.
3. At a voltage of 750 kV, there are four wires in each phase.
4. And at a voltage of 1150 kV, there are already 8 wires in one phase.

The reasons why this splitting occurs are as follows:

• Increase bandwidth.
• Reduce crown losses by reducing tensions.
• Reduced generation of RF interference.

Let's go over the above reasons in a little more detail.

As you already understood, such lines are created in order to transmit more power. Thus, the calculated current load on the 500 kV line is from 1000 to 1200 Amperes, for the 750 kV line it is already from 2000 to 2500 Amperes, and the 1150 kV line is capable of withstanding the current load up to 5000 Amperes.

Now imagine what section the wire should be in order to withstand such currents for a long time.

So the cross-section of such a wire should be from 1 m2 to 4 m2. Yes, this is not a mistake, from one square meter to four square meters.

It is clear that in order to produce such wires, special technology is needed. And it takes a lot of money and time to transport and install such a wire. In addition, the skin effect (surface effect) has not yet been canceled.

Consequently, the current will flow along the outer radius of the conductor, and the inner part will not be used.

But the ultra-high voltage around the EHV wires forms an electric field of increased intensity, which is the cause of corona discharges on the wires.

And this discharge also has a directly proportional dependence on the diameter of the phase conductor.

So if you place wires of one phase at the vertices of a regular polygon, then the system formed in this way can be represented as a single conductor.

And the higher the indicator of the tension level at which the corona discharge begins, the lower the corona loss.

When calculating and producing EHV lines, many more factors are taken into account, therefore such lines are unique in their kind and differ so much from "ordinary" lines 6/10/34/110/220 kV.

If you were interested to read about the splitting of the EHV phase wires, then like it and do not forget about the repost.

Thanks for reading to the end!