Why don't we use the Earth to transmit electricity?

Question

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

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.

There is a thing called impedance, have you studied that yet. — Gil, Apr 09 '23 at 23:34
It isn't very safe. For instance GFCIs and RCDs would no longer work with earth as neutral. — Andy aka, Apr 10 '23 at 10:51
@Kubahasn'tforgottenMonica: It worked well enough for nineteenth-century telegraphy. — supercat, Apr 10 '23 at 17:51
@Kubahasn'tforgottenMonica, the resistivity is high but the cross-sectional area can't be beat. — The Photon, Apr 10 '23 at 17:51
This was part of my answer. It was suggested that I remove it from the answer, so I'll comment instead... If you're a third-year undergraduate studying electrical engineering, I am deeply concerned about the quality of teaching at your university. This is basic material which should be covered early in the first year. If you're still asking basic questions about AC in the third year, either they've screwed up by not teaching you, or they've screwed up by letting you continue the course. One way or another, this isn't good. — Graham, Apr 11 '23 at 00:27
Smart career decision to go for power infrastructure engineering instead of aircraft, missile, and rocket science.. No layoffs! — richard1941, Apr 16 '23 at 15:34
Engineering ethics requires consideration for life forms that live in the soil; they are shocked by electric current, and this can be destructive where connection is made to the earth and the current density is greatest. Your environmental impact statement would be rejected by the political authorities. — richard1941, Apr 16 '23 at 15:39

score 25 · Answer 1 · edited Apr 10 '23 at 16:49

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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

edited Apr 10 '23 at 16:49

Doug Lipinski

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answered Apr 10 '23 at 00:38

Edin Fifić

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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. – richard1941 Apr 16 '23 at 15:43

Graham · Answer 2 · 2023-04-11T00:25:27.207

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.

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. — SoreDakeNoKoto, Apr 10 '23 at 23:21
@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. — Graham, Apr 11 '23 at 00:21

MikroPower · Accepted Answer · 2023-04-10T14:16:40.107

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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)

edited Apr 10 '23 at 14:16

answered Apr 09 '23 at 23:58

MikroPower

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The 3 phases are balanced, no current needs to flow in the neutral. – Mattman944 Apr 10 '23 at 01:45
Hence why we can just connect it to the ground with no power losses? P = I^2 * R = 0^2 * R = 0 – İbrahim İpek Apr 10 '23 at 12:32
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@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. – MikroPower Apr 10 '23 at 14:13
"*... only with 180° phase-shift ...*". I think you meant 120°. – Transistor Apr 10 '23 at 14:25
@Transistor - Oh right. 180 is nonsense, I should not try to be fast. 3x120°=360° – MikroPower Apr 10 '23 at 14:33
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@MikroPower That's solved by having the phases go imbalanced, not by having current through earth. – Hearth Apr 10 '23 at 15:34
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@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. – MikroPower Apr 10 '23 at 16:55
@Hearth - https://www.rotek.at/produkte/pdf-aktuell/Stromerzeuger/Generator_Allgemein_Grundlagen-3P-Netz_Rotek_DE_Bildschirm.pdf It is in German, the word "Ausgleichsstrom" (compensating current) between earth is important and not good visible in the image. – MikroPower Apr 10 '23 at 17:04
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@MikroPower Are we talking about the delta-connected long-distance transmission end or wye-connected consumer end? In the delta case, there is no ground reference at all, and that's what I'm talking about. – Hearth Apr 11 '23 at 03:06
@Hearth - Your power stations have no ground or neutral line? This would be to risky and the grid would have a bad quality. I mean there are areas with dry soil were it is impossible, but then you have an additional wire/line. – MikroPower Apr 11 '23 at 15:33
@MikroPower Power stations do, as do low-voltage service areas, but high-voltage transmission lines are delta-connected and have no ground reference. – Hearth Apr 11 '23 at 15:35
@Hearth - No. If I look at the transformer of our substation (here called "Umspannwerk"), then there are 4 ceramic isolators which are going into the transformer. 3 dick wires and one thin wire for the compensating current. You always have to deal with ground, if it is the compensating current or to recognize an error. – MikroPower Apr 11 '23 at 18:46

score 1 · Answer 4 · answered Apr 11 '23 at 07:21

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.

Why don't we use the Earth to transmit electricity?

4 Answers4