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'[EE]:: SWER - Single Wire Earth Return power trans'
2012\04\16@101042 by RussellMc

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  BCC: JMC - Any of these in Vanuatu?

1st reference is useful in spelling out the basic factors of concern
when designing an earth return power system.
Thee is a little more magic to it than may meet the eye.
Not something most people are liable to do very often. But ...

SWER = Single Wire Earth Return power transmission is essentially just
that. A single high voltage (say 10 kV to 30 kV) phase wire is used to
distribute power and the return circuit  uses ground. While this at
first and second blances may sound like very old technology (and it
is) it is also still of great use in niche applications. Medium length
rural distributions of moderate power requirement may still be most
cost effectively served by SWER.

I'm posting this mainly because of the excellent material in the first
link below.

http://www.stonepower.se/Images/SWER.pdf


Distribution of Electrical Power to Rural Areas-
Australian Experience and Implementation
Possibility in Developing Countries
http://www.iranenergy.org.ir/library/articles/5%20articles%20national%20energy%20congress/pdf/1406.pdf


Wikipedia
http://en.wikipedia.org/wiki/Single_wire_earth_return


Sci,Eng
http://groups.google.com/group/sci.engr.electrical.sys-protection/browse_thread/thread/5013cb01d9526811/3539d5ffb9062da4%3Fq%3D%2522High%2BVoltage%2522%233539d5ffb9062da4&ei=iGwTS6eaOpW8Qpmqic0O&sa=t&ct=res&cd=2&source=groups&usg=AFQjCNFy3KmggWtXV7X5hmiPPWIADmQw1g?pli=1


________________________________

This amused me, as an example test for the TECH / EE boundary is
things you cannot/can build at home and a power station is mentioned
as something that you (notionally) can't. . This is connected to a
power station and is on the large side of DIY but the expressions
given may indeed assist some DIY endeavours.




            Russell McMahon

2012\04\16@103643 by Isaac Marino Bavaresco

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It is used extensively in Brazil for small rural properties.
What annoys me is that most of Brazil uses 220V/380 3-phase but for
rural SWER the power companies only allow installation of bi-phase
127V+127V.
That's very bad, because I need to buy 127V lamps in a state that is
primarily 220V and my 220V electric tools must be connected to
phase-phase 254V (15% more voltage, 33% power overload) risking damage.


Isaac


Em 16/4/2012 11:10, RussellMc escreveu:
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>


'[EE]:: SWER - Single Wire Earth Return power trans'
2012\05\03@121035 by Electron
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Won't the return currents cause ionization in the terrain, etc.. possibily
with biological implications?


At 16.10 2012.04.16, you wrote:
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>

2012\05\03@144636 by Isaac Marino Bavaresco

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If I remember it right, the majority of return currents flow at 300 to
400 meters below ground.


Isaac


Em 20/4/2012 02:07, Electron escreveu:
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>> --

2012\05\03@152731 by Martin McCormick
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Electron writes:
> Won't the return currents cause ionization in the terrain, etc.. possibily
> with biological implications?

       I just red the pdf on the link and it did say that the
return currents were around 1200 meters down. I know that
alternating current is successfully used in meggers which are
magneto-based ohm meters for measuring soil conductivity. I
don't know what would happen over a long period of current flow
but as long as there is not a DC component, the continuous
reversal seems to prevent ionization.

       Neon and fluorescent lamps last much longer running on
AC than they do on DC. Also, some en clinometers use an
electrolyte in a sealed tube and they can be damaged by DC but
work fine on AC.

Martin McCormick
WB5AG

2012\05\04@102423 by Bob Axtell

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On 5/3/2012 3:27 PM, Martin McCormick wrote:
> Electron writes:
>> Won't the return currents cause ionization in the terrain, etc.. possibily
>> with biological implications?
>        I just red the pdf on the link and it did say that the
> return currents were around 1200 meters down. I know that
> alternating current is successfully used in meggers which are
> magneto-based ohm meters for measuring soil conductivity. I
> don't know what would happen over a long period of current flow
> but as long as there is not a DC component, the continuous
> reversal seems to prevent ionization.
>
>        Neon and fluorescent lamps last much longer running on
> AC than they do on DC. Also, some en clinometers use an
> electrolyte in a sealed tube and they can be damaged by DC but
> work fine on AC.
>
> Martin McCormick
> WB5AGZ
I also read the PDF thoroughly. I am inclined to consider the idea of transmitting
power through ground as unsound.

I see that, in theory, current will pass through the ground. But will it do so reliably?
Wouldn't the fact that soil holds a varying amount of moisture cause a differing
amount of conductivity? Wouldn't two metal poles placed in the ground 3' deep
and 50' apart measure a very different conductivity at night vs during the day,
because of the daytime evaporation of surface soil water?

Who says that the current flows deep under the ground (i.e., 1200m)? Why doesn't
it take the path of least resistance, like current normally does (I've never seen it do
otherwise in my entire life)?



This conversation is interesting because it MIGHT eliminate the need for a single
wire. Otherwise, it is starting to sound like the study of bumps on the head being
related to intelligence, or mankind causing global warming with automobiles  or
cows passing gas.

--Bo

2012\05\04@104742 by Justin Richards

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When measuring ground return for payphone metering in Aust (metering
no longer uses ground return) i was surprised to discover measurement
less than 50 ohms over km's

The only way i could explain away the low readings was to consider the
ground as many conductors in parallel.

..





On 04/05/2012, Bob Axtell <spam_OUTbob.axtellTakeThisOuTspamgmail.com> wrote:
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>

2012\05\04@105308 by Justin Richards

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the spec was < 50 ohms but the actual readings were less than 15 ohms
if memory serves

On 04/05/2012, Justin Richards <.....justin.richardsKILLspamspam@spam@gmail.com> wrote:
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>> -

2012\05\04@122357 by Isaac Marino Bavaresco

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Em 4/5/2012 11:24, Bob Axtell escreveu:
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Why could not at 1200m deep the conductivity be maximal? Perhaps rocks
full of metal ore, soaked in water?


Isaac

2012\05\04@122835 by RussellMc

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"What have you done with Bob " asked about reality and practicality of SWER
power lines.
__________

"SWER" power lines have a very long history and are highly useful. They
still have some very competent protagonists and a significant number are
still in use.

Engineers will be aware of the two dimensional concept of "Ohms per
square". If a 1 cm edge square of a given thickness of a uniform resistive
sheet has a given resistance between opposite parallel sides, then a 1
metre edge square or a 100m edge square of the same thickness of identical
material will have the same resistance edge to edge as has the 1cm edge
square. This is obvious on inspection as increasing the dimensions scales
up the path length and path width in equal ratio.  The resistance of
"ground" behaves similarly - here we are coupling into a half sphere about
the end points and we must deal with 3D curvilinear cubes (rather that the
more familiar 2D curvilinear squares) but the end result is similar. The
main issue in connecting a high energy ground path between two points some
km apart is coupling into the bulk ground at each end - the resistance of
"the earth" is not a problem - attaching to it is. As Bob adumbrates, it is
possible to make ground connections whose quality varies widely with local
conditions - BUT 'we' have centiries of experience of creating reliable
repeatable ground connections. All electric power administrations have
procedures which are required to b followed to produce an adequate  ground
connection for a given taks under worst case conditions.

The procedure do  indeed superficially appear somewhat similar to
phrenology but the comparison is illusory. Here the bumps on  a head are
replaced by soil types, water table, length and diameter and material of of
grounding pipes, sacks of Bentonite, and more. The ground protection
systems in Phase / Neutral / Safety ground systems in widespread use in
many countries depends crucially on the ability to make and maintain an
adequate safety grounds. The UK and NZ are two such - it seems 'from a
distance' tat US practice may be less stringent with some systems.

> Who says that the current flows deep under the ground (i.e., 1200m)?
> Why doesn't it take the path of least resistance, like current normally
does
> (I've never seen it do otherwise in my entire life)?

Here as in all systems, current flows in proportion to the applied voltage
and inversely in proportion to the resistance the voltage is applied over.
ie current does not take the path of least resistance but "takes the paths
of all resistances"  - from each according to its inverse resistance, to
each according to its applied voltage. But, I know that you know that.
The claim that current flow ***mainly*** at a depth of 200 feet is quite
possibly correct and if it is, is liable to be caused by non linear
compositions of real world strata and soil conditions  forming a path of
effective minimal resistance for power currents.



material will certain



On 5 May 2012 02:24, Bob Axtell <.....bob.axtellKILLspamspam.....gmail.com> wrote:

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>

2012\05\04@130655 by Dave

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Current takes all possible paths. It prefers the path of least impedance.
Isaac Marino Bavaresco <EraseMEisaacbavarescospam_OUTspamTakeThisOuTyahoo.com.br> wrote:

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>

2012\05\05@102057 by peter green

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Justin Richards wrote:
> The only way i could explain away the low readings was to consider the
> ground as many conductors in parallel.
>  
Right.

Let us consider a simplified case

Imagine a hemisphere of radius R made of a perfect conductor burried
with the flat of the hemisphere level with the surface in infinitely
extending ground of constant resistivity p with an atmosphere of
infinitie resistivity above it.

Now let us consider the soil round the hemisphere we can divide this
soil into an infinite number of infinitesimally thin hemispherical
shells of infinite resistivity. These hemispheres have a diameter of r
and a thickness of dr

The shell has an area of 2πr² and a thickness of dr so it's resistance
is p/(2πr²) dr

To cover all the shells now we integrate from r=R to r=∞

So our resistance becomes

(-(p/(2π∞))) - (-(p/(2πR)))

which simplifies to.

p/(2Ï€R)

In other words the resistance "to infinity" is a finite number! While
this is a simplified case the general principle holds for real
grounding, the issue is the resistance of the layers of material close
to your connections, far from your connections the area is so great that
the resistance becomes negligable.

2012\05\08@154931 by Barry Gershenfeld

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Interesting discussion, as always.  Also four days late, as always.   I
think if you trust the assertion of the resistance at several hundred
meters down, then the problem becomes assuring that your ground posts "get
connected to" the "underground expressway".  This isn't likely to happen at
50' separation, but at powerline company distances, it will.

As to that unfortunate folklore about the path of least resistance, If I
apply 10 volts across a 100 ohm resistor, paralleled with a 25 ohm
resistor, I simply calculate the current for the 25 and ignore the 100 :)
<-- don't miss the smiley :)

On Fri, May 4, 2012 at 7:24 AM, Bob Axtell <bob.axtellspamspam_OUTgmail.com> wrote:

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