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Think about it, instead of transmitting electricity in 2 wires, we could only use one:

my ingenious idea - le turkish wisdom

Why don't we just do it? I think they do it in three-phase transmission by connecting the neutral phase to the ground on both sides, why don't we replicate it in the monophase? Sorry if I sound idiotic, I just want to understand it properly. This is my third year studying electrical engineering, and as you can already understand, with this level of knowledge, in 1 year, I will be designing the electrical infrastructure which you power your computer on to screen this article, although it may sound scary. I would appreciate some help to curb my ignorance.

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    \$\begingroup\$ See: en.wikipedia.org/wiki/Single-wire_earth_return \$\endgroup\$ Apr 9, 2023 at 23:29
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    \$\begingroup\$ There is a thing called impedance, have you studied that yet. \$\endgroup\$
    – Gil
    Apr 9, 2023 at 23:34
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    \$\begingroup\$ It isn't very safe. For instance GFCIs and RCDs would no longer work with earth as neutral. \$\endgroup\$
    – Andy aka
    Apr 10, 2023 at 10:51
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    \$\begingroup\$ Earth is a piss poor conductor, relatively speaking. \$\endgroup\$ Apr 10, 2023 at 15:28
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    \$\begingroup\$ @Kubahasn'tforgottenMonica: It worked well enough for nineteenth-century telegraphy. \$\endgroup\$
    – supercat
    Apr 10, 2023 at 17:51

5 Answers 5

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In Germany we have power pole with 10kV and till 100kV powerlines, you can see there three phases, but the neutral wire is not there visible. This wire is not in the ground somewhere, it is the ground.

An example with different ways to connect the earth:
https://en.wikipedia.org/wiki/Earthing_system

Other people had the same idea like you, centuries ago. ;-)

But now we want to use DC, but there are some problem if you only use one wire and the earth, but some smart people have solved it too. (partly, it is not ideal too)

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    \$\begingroup\$ The 3 phases are balanced, no current needs to flow in the neutral. \$\endgroup\$
    – Mattman944
    Apr 10, 2023 at 1:45
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    \$\begingroup\$ @Mattman944 - If the current over all 3 phases is the same (same load), only with 180° phase-shift, then you have right with the 0 Ampere over the neutral line. But if you connect a town to this power-line and not a industrial complex, then this looks different. If you know the German systems, then you would know that the generator (Starpoint circuit) has a connection to ground, to be able to create a zero-point compensation, so that we do not have a very different voltage on every phase, even with a different load on each phase you have still around ~230V between neutral and each phase. \$\endgroup\$
    – MikroPower
    Apr 10, 2023 at 14:13
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    \$\begingroup\$ "... only with 180° phase-shift ...". I think you meant 120°. \$\endgroup\$
    – Transistor
    Apr 10, 2023 at 14:25
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    \$\begingroup\$ @MikroPower That's solved by having the phases go imbalanced, not by having current through earth. \$\endgroup\$
    – Hearth
    Apr 10, 2023 at 15:34
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    \$\begingroup\$ @Hearth - No, there is really a current over earth and you can measure it. If you would have right, then our power-stations, transformer houses, substations would not need a grounding any more. The problem is only, the world is not perfect, you have different loads on different phases. But we do not want that the zero point is moving, this would be bad, so we need a reference potential and this is earth. \$\endgroup\$
    – MikroPower
    Apr 10, 2023 at 16:55
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In some parts of the world that is actually done, but it has limits on the amount of power that can be run through a single line and delivered to a certain size area.

The reason for its limited use is a relatively high earth resistance, as well as the earthing/grounding issues due to that resistance.

You can see more details here https://en.wikipedia.org/wiki/Single-wire_earth_return and here https://www.sciencedirect.com/science/article/abs/pii/S0142061510001456

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  • \$\begingroup\$ Increasing the voltage decreases the current for the same amount of power. And decreasing the current reduces the impact of ground resistance (and wire resistance too). So go with very high voltage and save money on wire. \$\endgroup\$ Apr 16, 2023 at 15:43
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I think they do it in three-phase transmission by connecting the neutral phase to the ground on both sides

No they don't.

With a single phase, one wire is the "zero volts" reference and the other (live) wire has an AC voltage relative to that reference. You could, as you say, replace the "zero volts" reference with the actual ground, but as other answers have said you need to account for the impedance of the ground between one end of the grid and the other end (over however many kilometres). This is done pretty regularly for power transmission over the sea (to islands, for instance) because the impedance of seawater is rather low. The impedance of soil and rock is not that low, so it's generally a bad choice.

The basic principle of 3-phase though is that none of the wires are the "zero volts" reference. Instead, the zero volts reference is a star-connected point relative to all three phases. There is no "return path" through the earth, because that's not how it works.

There actually is a connection from the zero volts reference to earth, though. But that's purely to deal with the differences in electrostatic charge between the two ends of the grid system. It has nothing to do with providing a return path for the transmission current.

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    \$\begingroup\$ Erm, you know, people sometimes ask basic questions that are neither indicative of their education nor of their own aptitude -- it is seldom that deep. And even when it is, volunteering this in an SE answer helps nothing and is simply an exercise in condescension. You should remove that "aside" from your answer. \$\endgroup\$ Apr 10, 2023 at 23:21
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    \$\begingroup\$ @SoreDakeNoKoto It's not condescension - I am literally scared: for the OP; for everyone he may work with in future; and for people around him if he hasn't had the basic education to do his job safely. But I can move that to a comment if you would prefer. \$\endgroup\$
    – Graham
    Apr 11, 2023 at 0:21
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They do this exactly as you explained already.

In single-wire earth return (SWER) AC electrical distribution systems, costs are saved by using just a single high voltage conductor for the power grid, while routing the AC return current through the earth.

This system is mostly used in rural areas where large earth currents will not otherwise cause hazards.

Some high-voltage direct-current (HVDC) power transmission systems use the ground as second conductor.

This is especially common in schemes with submarine cables, as sea water is a good conductor.

Buried grounding electrodes are used to make the connection to the earth.

The site of these electrodes must be chosen carefully to prevent electrochemical corrosion on underground structures.

A particular concern in design of electrical substations is earth potential rise.

When very large fault currents are injected into the earth, the area around the point of injection may rise to a high potential with respect to points distant from it.

This is due to the limited finite conductivity of the layers of soil in the earth of the substation.

The gradient of the voltage (the change in voltage across the distance to the injection point) may be so high that two points on the ground may be at significantly different potentials.

This gradient creates a hazard to anyone standing on the earth in an area of the electrical substation that is insufficiently insulated from ground.

Pipes, rails, or communication wires entering a substation may see different ground potentials inside and outside the substation, creating a dangerous touch voltage for unsuspecting persons who might touch those pipes, rails, or wires.

This problem is alleviated by creating a low-impedance equipotential bonding plane installed in accordance with IEEE 80, within the substation. This plane eliminates voltage gradients and ensures that any fault is cleared within three voltage cycles.

Though to be clear because power loss and voltage drop along a distance is current dependent,

P_loss = R * I^2,

if the voltage is brought high enough and the current dropped low enough the touch voltage issues can be eliminated. This is because the voltage drop across virtually any distance across the earth ultimately goes to zero.

This also accounts for the increased resistance of the soil. If we step up the voltage by 3 orders of magnitude, 1000x, from the 100,000v typical transmission lines (obviously not the highest) up to the 50-100million volts Tesla was suggesting with his magnifying transmitter, then the current scales by x/1000.

And because P_loss = R * I^2

When current drops by 1/1000 the power loss drops by 1/1,000,000th of what it would be through copper lines. Even if the earth “wire” that was being used was just the diameter of the copper wire, the soil could have a resistance 1,000,000 times that of copper and it would have the same power loss over the same distance.

And the earth won’t have inductive and capacitive impedance losses to well… the earth, like suspended transmission wires do with the earth.

Then considering resistance is also inversely proportional to conductive area… R = rho * L / A A = pi * (Earth Radius)^2

When using the earths area to conduct electricity across anywhere on it the conductive area becomes the area of the earth, containing the earths diameter squared under the division sign. Which makes the resistance further plummet.

And the power loss to scale proportionally with that reduced resistance due to increased conductive area.

This was the basis for Nikola Tesla’s electricity system without wires that used the earth. Despite what many people have erroneously claimed, Tesla’s wireless system was NOT through the air.

Fully explained with animations in the following video.

🛜 Neil Degrasse Tyson, WRONG about Tesla?!? 🛜 ​⁠@joerogan (30min) https://youtu.be/teoyAdU-1S0

Tesla tried to use radio very early on but specifically said it wasn’t possible due to 1/r^2 dispersion issues.

“I then turned my attention to wireless transmission and was fortunate enough to achieve similar success in this fruitful field, my discoveries and inventions being employed throughout the world. In the course of this work, I mastered the technique of high potentials sufficiently for enabling me to construct and operate, in 1899, a wireless transmitter developing up to twenty million volts…”

Then in the very next breath he says…

“…Much time was devoted by me to the transmission of radiant energy, in various forms, by reflectors and I perfected means for increasing enormously the intensity of the effects, but was baffled in all my efforts to materially reduce dispersion…”

“…As will appear from the inspection of the drawing, the spherical frame of the terminal is equipped with devices, one of which is shown in the enlarged view below and comprises a bulb 2, of glass or other insulating material and an electrode of thin sheet suitable rounded. The latter is joined by a supporting wire to a metallic socket adapted for fastening to the frame 1, by means of nut 3. The bulb is exhausted to the very highest vacuum obtainable and the electrode can be charged to an immense density. Thus, it is made possible to raise the potential of the terminal to any value desired, so to speak, without limit, and the usual losses are avoided. I am confident that as much as one hundred million volts will be reached with such a transmitter providing a tool on inestimable value for practical purposes as well as scientific research.”

-Nikola Tesla

And for the record I do in fact have a degree in physics.

-Charlie Solis

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I think they do it in three-phase transmission by connecting the neutral phase to the ground on both sides

As a person in 230V-land, you surely know that power is distributed to homes as 3-phase "Wye" configuration and a house gets 1, 2 or all 3 phases, depending on need. However, that only applies from the neigbhorhood transformer to the home.

Of course you know, voltage is stepped up to a higher voltage for distribution to your neighborhood transformer.

You are presuming that the higher voltage distribution lines are also 3-phase "wye". They are not. They are 3-phase "delta" which has no neutral. There is no reason to distribute neutral at the higher voltages since all system loads are 3-phase. (as in, a whole neighborhood appears as a reasonably balanced 3-phase load).

It's true there is bonding between neutral and actual earth. However - the classic blunder is believing that makes them the same thing. It most definitely does not. That neutral-ground equipotential bond is to give the transformer output a reference to actual earth voltage, so that the 4 output wires (3 phases + neutral) aren't floating thousands of volts above actual earth.

By pegging neutral to earth, that means the 3 phases will not be more than 230V away from earth. This increases safety as compared to other options.

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