Talk:Single wire earth return

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[edit] Removed Tesla Reference from History

This text refers to a system that that does not use earth return. While rather interesting, it is off-topic. Perhaps it should be in a different article? Ray Van De Walker 03:53, 31 May 2006 (UTC)

At the end of the 19th century, Nikola Tesla demonstrated that by using a electrical network tuned to resonance and using, what at the time would be called, "high frequency", a single wire was necessary for power systems, with no need for a return conductor. In the spring of 1891, Tesla gave a demonstrations with avarious machines before the American Institute of Electrical Engineers at Columbia College. His lecture exhibited this feature, the chief import exhibited that all kinds of devices could be operated thru a single wire without a wired return. The one-wire transmission system was protected in 1897 by U.S. Patent 0593138 , "Electrical Transformer".

This patent diectly deals with this topic. And the text and Tesla's intentions in his one wire system is exactly a "Single wire earth return". 204.56.7.1

[edit] Clarification of grounding

I'm seeing a few articles mentioning how an earth ground is used as a "return path" for a circuit. Admittedly, my understanding of electrical engineering is very limited, but I was under the impression that the idea of a literal "return path" through the ground was disproven, and an earth ground is now understood merely as a "source/sink". Reading the article about SWER and ones that link to it, I'm getting impression that there's an electrical path through the ground from a user back to the power plant, which I'm pretty sure is not the case. Could this be clarified? -- User:NewtN Question copied here by C J Cowie 00:21, 8 December 2005 (UTC).

The earth can conduct an electric current, but electric power sources and loads are normally not connected to the earth in a manner that would allow the earth to be used as a return path between the source and load. In fact, power distribution systems are usually designed so that an accidental connection to the earth (a ground fault) will cause a circuit breaker to trip and disconnect the faulted load circuit from the supply.In an SWER system, there is an isolation transformer at the point where the SWER transmission line connects to the normal power distribution grid. One end of the secondary winding of that transformer is connected to the earth. At the load location, there is another transformer with one end of the primary winding connected to the earth. The use of two isolation transformers assures that the earth is used as a return path only between the two isolation transformer locations. -- C J Cowie 00:38, 8 December 2005 (UTC)

Thank you for the comments regarding the isolation transformers. I saw something to this effect in a circuit diagram of a SWER system and I shouldn't have skipped that very important point. My question regarding the terminology "return path" still stands, though. My understanding is that if you grounded these transformers in very large piles of earth that were totally separate and insulated from each other, the system would function equally well. Is that more or less accurate? If so, is "return path" merely a metaphor? If not, does that mean a wave of displaced ions is travelling through from one transformer to the next, heating the ground as their energy dissipates? -- NewtN

I have an electrical engineering degree and working experience, but I am not an SWEW expert, not even an electric power distribution expert. However, I hope that I have enough expertise to be useful. My comments are based on my understanding of some fundamental principles plus my understanding of what I have found on the internet:
http://www.ruralpower.org
http://www.eng-tips.com/viewthread.cfm?qid=122070&page=19 (This is a discussion about another subject, but it contains some comments about SWER in the middle of the main discussion.)
The term "return path" is not merely a metaphor. With SWER distribution, an electric current does actually travel through the earth between the transformers. Electrons are actually exchanged among the molecules of water and other conducting materials in the earth. Since electrons removed from one molecule are immediately replaced by electrons from adjacent molecules, I don't believe that ions accumulate or travel in the earth. There is certainly some power dissipated in the earth as heat, but that effect would be quite small. The transformer windings are connected to the earth by boring holes in the earth and inserting long copper-clad steel rods. If 2 rods were to be driven into the earth at 2 locations along the SWER path, it would probably be possible to measure a voltage between them. It appears that SWER systems are designed to limit the voltage in the earth to 20 volts per meter to avoid shocking people and animals that might be in the area.
SWER systems are used in isolated areas in Australia, New Zealand and various parts of Africa. --C J Cowie 21:31, 13 December 2005 (UTC)
Hi CJ. I added some details to the article just before I read your comments above, but we seem to be saying the same things. I didn't put in anything about the conduction mechanism, since I think that's too detailed for this article, but you might disagree. If you do want to discuss the subject, perhaps it would be better to start a new article on "ground currents" or something, since it will apply to many other articles besides this one. Regards, --Heron 21:57, 13 December 2005 (UTC)
Hi Heron. I had not heard of SWER before I saw User:NewtN's question at Talk:Electrical engineering. My own curiosity prompted me to try to learn enough to answer the question. I think that the brief description and links that now comprise this article are sufficient. Regards, --C J Cowie 23:40, 13 December 2005 (UTC)

[edit] Removed hidden comment from text, placed them in talk=

Make a reference note to these or leave them out. 204.56.7.1

Maintenance costs are roughly 50% of an equivalent line. numbers from Stone Power reference; 'regulation' from Mandeno who said that the costs were lower.

Steel's greater strength permits spans of 400 m or more, reducing the number of poles to 2.5/km. from Mandeno, who has an extensive discussion on this issue, also briefly but prominently mentioned by Stone Power

Reinforced concrete poles have been traditionally used in SWER lines because of their low cost, low maintenance, and resistance to water damage, termites and fungus. Local labor can produce them in most areas, further lowering costs. Mandeno developed concrete poles, as outlined in article below, and they have apparently become standard in these systems; ruralpower features them, and mentions that local production is an important point.

[several hidden] from Mandeno

standard operating procedure under Mandeno, below

the entire distribution upgrade sequence is ref. Stone Power, below

[several hidden] from Stone Power, below

ref. RuralPower.org

from presentation on Single Wire Ground Return Interties at Univ. of Fairbanks, about alaskan interties, above

[edit] Tesla references

Besides the one in the article, please read,

  • Nikola Tesla and the induction motor. CM Jarvis - Physics Education, 1970 - iop.org

Also, a simple book search will show that this is what tesla was doing. G.book search. 204.56.7.1 15:36, 2 June 2006 (UTC)

This is interesting, @ the patents of Tesla it states that his patent is cited by U.S. Patent 6104107  (Method and apparatus for single line electrical transmission). 134.193.168.236 18:42, 2 June 2006 (UTC)

[edit] Theft reference

"SWER and conventional single wire rural electrification is generally installed in remote areas and can be prone to energy theft. Methods of countering this include centralized metering at the distribution transformer, prepayment meters and the use of neutral screen service drop cables. " For this to occur a thief must install a transformer and an effective earthing system. Energy theft in a developed country typically occurs by bypassing or in some way retarding the customers meter. In a developing country illegal connections direct to the low voltage street circuits would be more common. In either case comnnections direct to the HV system would be rare. If there is no major objections I will remove this point. Steve 23:04, 15 June 2006 (UTC)

Otoh SWER brings up an intersting possibilty for theft of its own and that is magnetic coupling to the line itself. Not sure how feasible it would be but it would certainly be interesting to run some calculations. As the current in the line is unbalanced it shuold be possible to pick up some significant magnatism without needing to get dangerously close to the line. Plugwash 18:52, 25 September 2006 (UTC)
I vaguely recall Mythbusters having a go at this concept and busting it Lumberjack Steve 00:28, 27 September 2006 (UTC)
If they did i suspect it was for a normal line not a SWER (as SWER basically doesn't exist in the USA). Mythbusters is a long way from rigours science! Plugwash

[edit] Take a look at the Image:Polemount-singlephase-closeup.jpg

It's s SWER transformer, the image is taken in CANADA and the history section of the article doesn't mention that SWER lines are used in CANADA.

It's a single bushing transformer but we can't see the overhead line - could well have the neutral wire run overhead. Common as dirt in rural distribution and does not in the least imply earth return. SaskPower Saskatchewan runs some SWER lines for the same reason the Australians do -remote farms many miles apart. --Wtshymanski 17:59, 18 July 2006 (UTC)

I suspect that there is a neutral return wire for this image - you can see a wire running up the pole seperate from the wire to the bushing. Quite common when the economics of the network require SWER but the earth return is not of a high quality ie sandy soil, hard rock etc. Lumberjack Steve 23:14, 18 July 2006 (UTC)

(following comment also posted earlier on talk:split-phase) looking at http://wearcam.org/christina/billru_cottage/d325.jpg which appears to be a larger view of the photo in the article and some of the related images on http://wearcam.org/christina/billru_cottage/polemount.htm it looks like the horizontal wire in the picture is a neutral of some kind with the phase wire being higher up on the pole. Plugwash 00:13, 19 July 2006 (UTC)

[edit] wouldn't it be more sensible

to have mutliple SWER lines out of phase with each other from a single distribution point to keep the earth currents at the distribution point down? Plugwash 01:15, 18 July 2006 (UTC)

Yes, that's a great idea. But how is the result any different than standard 3-wire systems?
I was thinking the lines would all start at one point (so you wouldn't have high earth currents at the starting point) but then go off in different directions to supply different loads. Plugwash 21:10, 21 October 2006 (UTC)

[edit] SWER cost

Obviously it only requires half as many conductors as a two wire system, and 1/3 as many conductors as a 3 wire system -- but the cost of the wire itself is one of the smaller costs in a electric power transmission system.

The article gives 2 other reasons SWER costs less than 2-wire systems:

  • SWER's high line voltage and low current permits the use of low-cost galvanized steel wire. Steel's greater strength ...

Huh? No, steel is not stronger than the material used in 2-wire systems. And 2 wire systems also use high voltage / low current.

  • SWER also reduces the largest cost of a distribution network, the number of poles. Conventional two wire or three wire distribution lines have a higher power transfer capacity, but can require seven poles per kilometre, with spans of 100 m to 150 m. SWER ... reducing the number of poles to 2.5/km.

OK, so we go from 7/km to 2.5/km. That's wonderful, but why?

Why does SWER need fewer poles?

It can't be because the cables are stronger. (The material used in SWER systems isn't any stronger than the steel cables used in 2-wire systems).

I could speculate that with 2 or more wires, we need more poles to keep the lines from swinging into each other and sparking. While with 1 wire, we just need enough poles to keep the lines from hitting the ground.

But perhaps there is some other reason? --70.189.77.59 21:04, 21 October 2006 (UTC)

[edit] Some ecologists claim bad influences of electrochemical reactions, but they do not occur on very large underwater electrodes.

They do occur, the question is how much, and what's morally acceptable.

"The advantage of such schemes is saving money for a second conductor, because the saltwater is an excellent conductor. Some ecologists claim bad influences of electrochemical reactions, but they do not occur on very large underwater electrodes."

The amount of reaction occuring is relatively small compared to what's expected from the line's power rating, because most of the energy in a high voltage line is delivered by high voltage and relatively small currents flow, so the power P=I*V is large, while the power loss, dependent only on current and resistivity of wire, I2Rstays low. I.e. if the same line carried 800,000 volts, or 101 volts and 1 amps over a 100 ohm line, the IR voltage drop in both cases would be dV=IR=1*100=100 Volts, delivering 1 volt on the other end of the wire out of a 100 V input, or 99% loss, compared to 799,900 output out of an 800,000 V input, or less than 1% loss. This is the reasoning for high voltage, limiting the amps that cause voltage drop, but it's also a reasoning to limit the electrochemical reactions, which as voltage independent and only depend on current, based on Faraday's law of electrolysis.

m = 1 / F * A / n * I * t

where F=96485 Coulombs/mole charge, the Faraday constant

A=atomic mass, 35.5 g/mole for chlorine atoms from seawater, 16 g/mole for oxygen

n=charge per atom, 1 for chloride ions, 2 for oxygen ions

I = amperage, t=time in seconds

So an 8 amp line would generate m=1/96485*35.5/1*8*(24*60*60)=254 g of chlorine gas in a day, equivalent to dumping 25,400 g of 1% wt bleach, or about 25 kg, 25 liters, about 6-7 gallons of straight bleach into the ocean per day at the titanium cage site in question. The sea and sea biosystems buffer and nullify most of these effects - the ocean is a big place - though there is a theoretically limited buffer capacity, how much is too much. It would be nice to have a study on how much this affects a local ecosystem, compared to, say, human fishing and fish eating, or waste treatment plant effluent releases, on a relative scale, on a dollar per dollar basis - if you can put a dollar sign on damage to the environment due to fishing - and what's acceptable. Humans do inflict some damage on the environment to sustain themselves, including taking over areas from wildlife for agriculture, hunting, fishing, etc., question is how to optimize actions to get the least environmental damage for greatest benefit. For instance fishing is a "natural" process that's been around for millions of years, while chlorine and oxygen induced damaged dna might induce ecosystem changes that are far too great compared to, say, sunlight uv and cosmic ray and seawater uranium decay inflicted dna damages. By the way most public utility drinking water is either chlorinated, oxygenated/ozonated, or treated with UV, to destroy most organisms, and such water, if allowed to stand for long, the organisms that haven't decayed remultiply and the water becomes stale. It's amazing how life is both so fragile and so resilient at the same time. Sillybilly 13:03, 8 November 2006 (UTC)

[edit] Good article

It's been a while since I last looked her and the article has become a very good reference piece on SWER. It has presented what can be a very confusing engineering concept in simple terms. Well done. Lumberjack Steve 22:42, 24 January 2007 (UTC)

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