AC Electricity Generation and Transmission over a Single Wire?

[aemla]

I'm a bit confused as to why can't you transmit AC current over a single wire.
For instance, say you have an AC generator which induces potential difference at different points of the wire and thus, creating current. Downstream, the wire can be split and applied to a load. When the wire is split, no current occurs because electrons have no where to go. What if, on both ends of the wire, you add a "cap" made up of positively doped material (boron for example), wouldn't that allow electrons to move back and forth at the frequency that they are generated??

Would really appreciate some insight on this concept.

 

[nsaspook]

It's not very clear what you're saying about transmit AC current as that implies moving something extra that wasn't already there instead of moving charges that already exist in the conductors back and forth a bit. Maybe you mean energy instead of current.

A single wire where there is a potential difference phase shift at different points of the wire is usually called an antenna when it launches EM energy into far-field space instead of being confined around the conductor.

You can transmit RF AC power as waves with a single wire if the frequency is sufficient to allow the single wire to behave as a waveguide for the propagating surface wave. That's not something you will see at utility line frequencies.

https://en.wikipedia.org/wiki/Single-wire_transmission_line#Single_conductor_waveguides

 

[davenn]

I'm a bit confused as to why can't you transmit AC current over a single wire.

you can it's very common ... why do you think you cannot ?

That's not something you will see at utility line frequencies.

Actually you can see that ... this topic has come up in the past and I remember then talking about
SWER ( Single Wire Earth Return) systems. Very common in rural areas over longer distances very economical as there is only one conductor to pay for.
my old home country of New Zealand have a lot of them.

an example from somewhere around the world ...

You can transmit RF AC power as waves with a single wire if the frequency is sufficient to allow the single wire to behave as a waveguide for the propagating surface wave

not so commonly done, I have only ever seen one example where a fellow ham operator set one up on the 1296 MHz ( 23cm) band ... pretty coolDave

 

[nsaspook]

Actually you can see that ... this topic has come up in the past and I remember then talking about
SWER ( Single Wire Earth Return) systems. Very common in rural areas over longer distances very economical as there is only one conductor to pay for.
my old home country of New Zealand have a lot of them.
...
not so commonly done, I have only ever seen one example where a fellow ham operator set one up on the 1296 MHz ( 23cm) band ... pretty coolDave

Sure, Ground return is really just a current electricity loop with a lossy ground wire.

Single wire transmission is a EM surface wave propagation mode. It's something we used at shortwave across a conductive plane like the surface of the earth. The common term is a ``ground wave'' with the Earth's surface as the 'single' conductor for the surface wave component of the received signal.

https://www.electronics-notes.com/articles/antennas-propagation/ground-wave/basics-tutorial.php

 

[sophiecentaur]

I'm a bit confused as to why can't you transmit AC current over a single wire.

One possible reason that it is not used more often is that high power AC generation and AC machines are very efficient when Three Phases are used. One option for the system is to transmit power using the Delta configuration in which there are just three wires - one for each phase between substations.

For short transmission legs, the expense of a good Earth Mat might lessen any advantage for a single wire system. So we are left with a few instances of long distance, medium power transmission requirements where a single wire is best.

That's not to say that there aren't places where they just never considered single wire distribution. Commercial operators can be very conservative in their attitude.

 

[davenn]

Single wire transmission is a EM surface wave propagation mode

yes, which as I stated in the second part of my reply

The common term is a ``ground wave''

and being a ham radio operator ... of course I'm very familiar with that mode

 

[sophiecentaur]

Single wire transmission is a EM surface wave propagation mode.

In the context of RF yes but single wire transmission of AC Power is really 'Earth Return'. This thread has dealt with both uses of the term but I think AC Power means 50/60Hz supply to homes.
The Goubau line form of RF feeder works well (reputedly) but has not been that popular. I wonder why.

 

[nsaspook]

In the context of RF yes but single wire transmission of AC Power is really 'Earth Return'. This thread has dealt with both uses of the term but I think AC Power means 50/60Hz supply to homes.
The Goubau line form of RF feeder works well (reputedly) but has not been that popular. I wonder why.

As usual it depends on your experience in a particular field. Personally I think the term 'single wire transmission' should be very distinct in electrical engineering from Single-wire Earth return (SWER) when addressing electrical transmission at any frequency as there are EM ground wave propagation modes for ELF waves below utility line frequencies used mainly for submarine communications. That is what I was trying to convey.

I think the availability of high quality coaxial cables made the Goubau line obsolete except in special conditions.
http://accelconf.web.cern.ch/AccelConf/ipac2017/papers/wepva134.pdf

We plan to use a novel technique based on technique that uses a Goubau line (G-line) to evaluate the impedance of the remaining critical APS-U vacuum components. The G-line is a dielectric coated single wire transmission line based on the principle of Sommerfeld-like surface waves [5]. A surface wave propagates in the interface between the central conductor and thin dielectric material coated on its surface. Surface-wave based transmission line permits RF energy to be launched on the wire, travel though a beamline component, and then finally be absorbed in a load.

http://accelconf.web.cern.ch/AccelConf/ipac2018/papers/thpak005.pdf

 

[anorlunda]

The OP has not yet returned to PF to read most of these replies.

I do not think the OP question was about SWER, or ground planes, but rather the very frequent confusion about what a closed circuit means when it is earthed at some point.

 

[tech99]

I think you are correct that if a sink can be found for the electrons then a current will flow. However, a piece of material containing holes is not a sink. The entire piece of Boron will rise and fall in potential together.
A current sink can be a large piece of metal, or a length of wire, say, and then we see a single wire mode of transmission. It is not necessary for AC that the two sinks are connected, as with an Earth-Return circuit. The sinks need to be of significant size relative to the wavelength, so we are talking about high frequencies here.

 

[sophiecentaur]

if a sink can be found

A Capacitor or and Electrolytic cell ? Many Farads of Capacitance needed. Edit - for low frequency use.

 

[tech99]

A Capacitor or and Electrolytic cell ? Many Farads of Capacitance needed. Edit - for low frequency use.

You cannot use anything like this because the whole capacitor rises and falls in potential together, so it is not doing any charge storage. You need a big object having capacitance to the rest of the universe. A wire having a length of a quarter wavelength will be quite good, although it wil lose some energy to radiation. Or a metal disc with a radius of a quarter wavelength.

 

[anorlunda]

We are driving ourselves crazy here because the OP never returned since posting to clarify the question. So we don't know what the "it" is that we're debating.

I'm going to close the thread for now.

@aemla , if you want to reopen this thread, click on my name and then start a conversation.

 

[anorlunda]

The OP did return and he requests that the thread be reopened. He also sent me with two PMs that rephrase his question. I'll post them below.

I'm getting the sense that it is possible to pass AC through a single wire at low frequency but still not understanding why.

As far as your reply goes, I guess if you do take a time slice, you can determine the distance that a charge (electron) has traveled (although a bit more complex with AC as potential would vary with time). If you displace that distance with holes like Boron atoms (tech99 said this won't work due to unchanging potential but I'm not sure I understand that, wouldn't there be a potential difference between empty holes and full, this difference would decrease as the holes filled?), you should be able to pass current through that specific distance, however, with DC this will not be a measurable effect since holes will be filled up and electrons have nowhere to go, whereas, with AC it will be if the Boron material is long enough.

 

[anorlunda]

Your question implies misunderstandings.

First, electrons to not travel very far with power frequency AC; not far enough to come out the other end.

Second, trying to understand electrical conduction at the individual particle level is nearly impossible at the B level.

The I level answer is The Drude Model. The A level answer is the Free Electron Model, and understanding that involves quantum mechanics.

Your attempt to self explain with electrons and holes is very wrong.

If you want analogies, like water flowing in a pipe, or a pipe filled with ping pong balls, PF is not the right place for that.

I know it frustrates many students, but sometimes very important concepts require years of study to understand, and there are no easy intermediate steps.

If you want to work at study, the next logical step is study of electromagnetic fields. But those are not molecular level.

 

[aemla]

I was really hopping this wouldn't come down to understanding quantum mechanics. I understand the results and interpretations of such physics but very little in between.
So the conclusion of this tread is that you must have a return circuit (either it's a self and parasitic capacitance on the same wire or some sort of second conductive plane).
Next, I'm going to look into the exact difference between classical and quantum free particle to further understand the outcome above.
Thanks for all the replies!

 

[sophiecentaur]

I was really hopping this wouldn't come down to understanding quantum mechanics

It certainly doesn't. It's a totally Classical EM problem which is not helped in the slightest by trying to bring in photons to the situation.

 

[anorlunda]

It certainly doesn't. It's a totally Classical EM problem which is not helped in the slightest by trying to bring in photons to the situation.

Sorry, that's not true. It does not use photons but it does use Fermi-Dirac Statistics and the mean free path of particles in a crystal. See https://en.wikipedia.org/wiki/Fermi–Dirac_statistics

I recommend that you read the entire Free Electron Model wiki article. It is not about a solution of Maxwell's Equations.
https://en.wikipedia.org/wiki/Free_electron_model

 

[aemla]

As I do research on the topics above, a quick and related followup on the question. What is it meant by "return circuit"? I used to think it's simply return of electrons, but I guess it's more of a charge path which might not necessary mean electrons. Is that right?

 

[nsaspook]

In most simple cases the "return circuit" is a current convention about how we reference potentials between points instead of a physical direction for charge to move back to a source.

A slightly complex DC example of return circuits where some charges are electrons and some are positive ions (arc supply) in a operational arc chamber.

 

[Nik_2213]

IIRC, there was a related query on another forum (Old EDA?) for ways to transfer micro-power to LEDs dangling off a single wire. In parallel. No 'Earth Return'.

Okay, it was to enhance their big polygrammatic (sp?) 'McGuffin' for a Lovecraftian LARP adventure by lighting its pretty plug-in 'Carnacki Crystals'. Sadly, they'd only thought to fit a single 4mm banana plug & socket at each 'node'...

KISS answer: Swallow the 'sunk cost', change out those plugs / sockets for phono or, preferably, ¼" jack.

'Mad Science' answer: Put each micro-power LED across a tiny LC tank circuit and base-drive those 'crystal sets' at resonance. Seems there could be just enough 'ornamentation' wrapping each mounted crystal to provide an antenna of sorts...
;-)

 

[anorlunda]

As I do research on the topics above, a quick and related followup on the question. What is it meant by "return circuit"? I used to think it's simply return of electrons, but I guess it's more of a charge path which might not necessary mean electrons. Is that right?

Simple answer: Take just the simplest element such as a AA battery. No current leaves the plus terminal unless the same amount of current enters the negative terminal. (Note that electrons are minus, so electrons flow the opposite direction of current.) A battery with only one wire attached can not deliver current, not matter what the voltage. With two wires it can. The wire connected to the negative terminal we call "return".

Complex answer: You keep adding new things to your questions. Electrons are not the only way to get current, an ion or any charged particle can be the transporter.

All others, please remember that this OP is asking B level questions. Please refrain from RF or micro current extreme examples. That is not what the question is about.