Do some utilities really use the EARTH as a sole return conductor?
Zorin the Lynx
that sometimes utilities use the actual ground as the return conductor
for high voltage transmission lines. I always thought that this would be
a poor choice, since:
1) The earth is not very conductive, compared to even a thin metal wire,
2) The conductivity it does have varies all the time; IE it gets more
conductive when the soil is wet after a rainstorm than when it's bone
dry. This would cause voltage fluctuations given a constant demand. If
it got too dry, there might be too much resistance to cover the load and
power failures would result, and
3) Voltage gradients could result if there is a patch of less conductive
earth along the path of the current.
So.. do utilities ever really use the ground as a sole return conductor?
I know that in WYE distribution there is a grounded conductor, but
it's generally an actual wire that is simply additionally strapped to
ground.
-Zorin
John Russell
Yes, I've come across a couple of utilities that use single-line
earth-return for small remote consumers.
Your arguments against it are based on the assumption that the return
current path follows the line and stays close to ground level. It doesn't.
At each end the neutral is taken through an earth rod and, effectively,
connects to the mass of earth at zero potential. If the earth resistance
of each rod is 1 ohm to earth then the effective resistance from end to end
is 2 ohms. For a load of, say, 100kVA at 6kV line voltage a resistance of
2 ohms is negligible in terms of volt drop and stays constant regardless of
length of line. The volt drop on the wire does, of course, increase but
with only one wire to drop voltage you can get twice the distance (if you
are volt drop limited) at half the cost.
--
John Russell
Consulting Engineer
Zorin the Lynx
> connects to the mass of earth at zero potential. If the earth resistance
> of each rod is 1 ohm to earth then the effective resistance from end to end
> is 2 ohms. For a load of, say, 100kVA at 6kV line voltage a resistance of
> 2 ohms is negligible in terms of volt drop and stays constant regardless of
> length of line. The volt drop on the wire does, of course, increase but
> with only one wire to drop voltage you can get twice the distance (if you
> are volt drop limited) at half the cost.
If the resistance from the rod to ground is one ohm each, and this makes
the total resistance two ohms, this seems to suggest that the Earth is a
superconductor. How is this possible, when rock and dirt aren't even
good conductors?
It doesn't make sense. Perhaps someone can explain this or direct me to
a web page that does?
-Z
Jim Ghrist
huge.
"Zorin the Lynx" <ya...@zorin.org> wrote in message
news:bkf1oi$hbm$1...@ottoman.cs.fiu.edu...
Peter
wrote:
>So.. do utilities ever really use the ground as a sole return conductor?
> I know that in WYE distribution there is a grounded conductor, but
>it's generally an actual wire that is simply additionally strapped to
>ground.
>
My understanding that the single wire earth return (SWER) system was
pioneered by Lloyd Mandeno a consulting engineer in New Zealand and
they were nicknamed 'Mandeno's clotheslines' by those who held the
system in disdain. For very small loads, galvanised iron wire
(intended for farm fences) was used. It is possible that it was
independentally developed elsewhere.
Lloyd was engaged by various Electric Power Boards (a bit like rural
cooperatives) to design and make business cases for reticulation in
sparsely populated areas.
In the New Zealand situation there is usually an isolating transformer
11/6.35kV for earlier systems and 11/11kV later on and to minimise
interference to telephone lines, the maximum current was 8 amps (I
think this may be relaxed if appropriate assessments are made).
In South Australia I noticed that the SWER conductor was connected to
one of the main feeder phases which would be OK as long as the zero
sequence load remained below the earth fault protection relay setting.
Fleaman
distibution lines. Only one Conductor and lots of ground rods at each
transformer.
"Peter" <pet...@parazzdise.net.nz> wrote in message
news:3f6b6c25...@news.paradise.net.nz...
James
> think this may be relaxed if appropriate assessments are made).
>
> In South Australia I noticed that the SWER conductor was connected to
> one of the main feeder phases which would be OK as long as the zero
> sequence load remained below the earth fault protection relay setting.
Link www.ruralpower.org has a lot of info on the system.
has a lot of info on SWER there. It is used quite extensively in some
areas of rural australia, though not in the state i live in. The
standard drawings Ive seen for it state the voltage at 19kV. There are
problems with it, but if you dont have any other choice, its a lot
better than having to generate your own power, running a diesel 24/7
aint cheap.
One of the biggest problems ive heard it that SWER lines have been
snagged by planes, helicopters, gliders as they are hard to see from
the air. The wires are very thin, one a single wire and the poles are
small and can be a few hundred metres appart. And in farm areas they
generally snake their way accorss fields and paddocks, taking pretty
much a direct route from house to house.
Never done anythig with them myself, but Ive heard the fun starts when
the earth wire breaks on the primary of the transformer, sending 19kV
into the house.......
cheers
James
Gary Tait
wrote:
>Alberta and Saskatchewan Canada, use the earth ground on all of their rural
>distibution lines. Only one Conductor and lots of ground rods at each
>transformer.
Are you sure it is in rural areas? In urban areas, where one
transformer serves several homes., the same wire used for the LV
neutral is often also the HV grounded conductor, and my be confusing
some.
Charles Perrin
>Never done anythig with them myself, but Ive heard the fun starts when
>the earth wire breaks on the primary of the transformer, sending 19kV
>into the house.......
Or the ground lead gets ratty, resulting in a voltage between the cow
waterer and earth.
I've read cases of dairy cows that failed to thrive for what was
obvious reasons once they figured it out!
--
Offshore a CEO: buy an ADR!
Robert Casey
>Resistance = Resistivity·Length÷Area. The area of the earth path is pretty
>huge.
>
>
>
Also the electricity will find its way down to the water table.
Higher conductivity.
Even a lousy conductor can be serviceable if you have a large
cross section area of it.
Fleaman
urban areas, but in rural prairies, the is more cost effective to omit the
neutral and drive ground rods.
"Gary Tait" <ta...@hurontel.on.ca> wrote in message
news:92somvsrnjfh841ug...@4ax.com...
s falke
"Fleaman" <jasa...@telus.nothing> wrote...
> Alberta and Saskatchewan Canada, use the earth ground on all of their rural
> distibution lines. Only one Conductor and lots of ground rods at each
> transformer.
It looks downright unbelievable at first take. On seeing it in Alberta a
couple of decades ago, a call to the electric utility {IIRC, in Calgary}
revealed that SWER was indeed used for rural customers. A single-bushing
14.4kV-120/240V transformer had two driven rods—at the transformer pole and
second pole out. A neutral span between poles connected two rods, the
transformer can and H2/X2. The utility conducted periodic ground-resistance
tests.
Each transformer was apparently limited to something like 15kVA, making the
hi-side ground current about an amp.
Ground-overcurrent relaying for that distribution circuit must have been about
as useful as an ashtray on a motorcycle.
--s falke
Matthew Beasley
"s falke" <bus...@pacbell.net> wrote in message
news:XP7bb.1863$BU4...@newssvr29.news.prodigy.com...
>
> "Fleaman" <jasa...@telus.nothing> wrote...
> > Alberta and Saskatchewan Canada, use the earth ground on all of
their rural
> > distibution lines. Only one Conductor and lots of ground rods at
each
> > transformer.
>
> It looks downright unbelievable at first take. On seeing it in
Alberta a
> couple of decades ago, a call to the electric utility {IIRC, in
Calgary}
> revealed that SWER was indeed used for rural customers. A
single-bushing
> 14.4kV-120/240V transformer had two driven rods—at the transformer
pole and
> second pole out. A neutral span between poles connected two rods, the
> transformer can and H2/X2. The utility conducted periodic
ground-resistance
> tests.
>
> Each transformer was apparently limited to something like 15kVA,
making the
> hi-side ground current about an amp.
When I first installed my service, out of curiosity I measured the
ground electrode conductor current. With no loads on, I had over 4 amps
of current and I am on the end of the line. (Way out on the end.)
I don't have water or gas utilities so their isn't stray current coming
in that way. When I connected up the well ground wire (grounded to pump
motor and well casing) the ground current to the pump house was about
1.6 amps.
The service is 7.2kV primary with one phase and neutral / ground. One
pole back there is all three phase conductors that feed my neighbors
irrigation pump. (Pump wasn't running at the time either).
Sounds that for SWER I would have LOWER earth currents than I have now.
>
> Ground-overcurrent relaying for that distribution circuit must have
been about
> as useful as an ashtray on a motorcycle.
Just curious... for the US application of Y-Y transformers for three
phase or phase to neutral/ground for single phase how common is ground
over current relaying? My utility has only single phase distribution
reclosers for both the substation and out on the line. (In addition to
fuses for branches).
>
> --s falke
>
>
>
Matthew
Matthew Beasley
"James" <j...@octa4.net.au> wrote in message
news:9c685cb8.0309...@posting.google.com...
-snip-
> Never done anythig with them myself, but Ive heard the fun starts when
> the earth wire breaks on the primary of the transformer, sending 19kV
> into the house.......
>
> cheers
> James
I thought that they had separate grounds electrodes for the primary just
for this reason. Of course the broken off end of the ground electrode
conductor would then rise to near primary potential. I wonder how many
pole fires have started from this? (Unless the ground electrode
conductor is insulated for primary voltage, which I would doubt.)
Matthew Beasley
"Zorin the Lynx" <ya...@zorin.org> wrote in message
news:bkcsj7$oli$1...@ottoman.cs.fiu.edu...
> I've always been curious about this. I thought I've heard in the past
> that sometimes utilities use the actual ground as the return conductor
> for high voltage transmission lines. I always thought that this would
be
> a poor choice, since:
> -Zorin
>
I can verify that this is done in the United States for the Oregon Caves
located right near the California border. (At least it was 3 years ago
when I visited).
I didn't notice right at the isolation transformer but I did double back
once I noticed the single wire. Right off of US 199 is the isolation
transformer. One secondary bushing was connected to the SWER line
conductor and the other had a separate line down to the ground rod that
didn't connect to the feed line ground conductor.
Based upon the short insulators that it must be a fairly low voltage,
something like 2.4kV. It's about 20 miles up to the caves. About
2/3rds of the way in the conductor is above ground, often using trees as
supports. The final 1/3rd is underground with signs that it was
originally above ground the whole way. If the underground conductor was
shielded it must have added an additional wrinkle... several miles of
charging current must also be lead off to ground. At the lodge for the
caves the buildings are fed by pad mount transformers. I can't comment
on the grounding arrangement there since I didn't open them up ;)
I did comment to my wife that touching the case might be a bad idea.
Matthew
Peter
<beas...@teleport.com> wrote:
>Just curious... for the US application of Y-Y transformers for three
>phase or phase to neutral/ground for single phase how common is ground
>over current relaying? My utility has only single phase distribution
>reclosers for both the substation and out on the line. (In addition to
>fuses for branches).
>
Several years ago some organisation was developing a relay that would
respond to electrical 'noise' associated with a typical earth fault
(conductor on ground etc). The idea was that it would be more
sensitive to ground faults than the usual zero sequence relay.
I have not heard anything since.
s falke
"Matthew Beasley" <beas...@teleport.com> wrote...
>
> Just curious... for the US application of Y-Y transformers for three
> phase or phase to neutral/ground for single phase how common is ground
> over current relaying? My utility has only single phase distribution
> reclosers for both the substation and out on the line. (In addition to
> fuses for branches).
On the North American continent, there are a lot of utilities, so there are a
lot of varied regional practices. ø-ø and ø-n distribution primary
connections are both used, with ø-n probably more common, for it allows for
economic insulation grading, ANSI standards recognize "one bushing" and "two
bushing" transformers as standard. Much distribution is 14.4kV and below, but
expansion tends to be at higher voltages, like 22-34.5kV. At 34.5, it's
understandable why 19.9kV {grounded-tank} single-primary-bushing pots may be
chosen over 34.5kV two-primary-bushing pots.
Then for example, in overhead distribution-circuit upgrades, a 12kV circuit
could be converted to 20,780V by insulator changeout, and stringing a mid-pole
neutral conductor with each 1ø of 2- or 3-pot 3ø transformers reconnected from
ø-ø to ø-n. Correspondingly, padmount 3ø transformer can be furnished with a
hiside delta-wye off-load switch to allow for future upgrades. In that case,
URD-cable insulation has a higher not-yet-used rating, like 25kV- where
15kV-class might be OK initially.
--s falke
Matthew Beasley
>
> "Matthew Beasley" <beas...@teleport.com> wrote...
I wasn't clear that I was not saying that North America is strictly ø-n,
just that it's increasing in prevalence. Between the danger of
ferroresonance and the dropping of additional fuses from faults it seems
that the trend is to ø-n vs ø-ø. Additionally many three phase
transformer banks with delta connections are being replaced Y-Y if /
when possible for the same reasons. (I'm talking just distribution
here.)
Anthony Seipolt
for rural and remote distribution.
The local terminology is SWER (Single Wire Earth Return). The previous post
was right in that a large number of earth rods are required at each
Transformer, as well as a redundant earth. The redundant earth protects
agaisnt the failure/damage to one earth.
Farmers have been know to crop too close to the pole and damage the earths -
thus resulting in a significant voltage rise at the break-point (very
occassionally resulting in lethal consequences for catttle).
The SWER voltage is usually 19kV or 12kV depending on the source system.
Supply voltage is typically 240/480 (180deg phase angle).
SWER systems are usually strung with 3/12 steel conductor and easily manage
spans of 300 metres or more. Maximum currents are usually about 40amps.Great
for covering the large distances of the Australian country-side at minimum
cost.
Anthony
"Fleaman" <jasa...@telus.nothing> wrote in message
news:vR6bb.4806$Vr3.2...@news1.telusplanet.net...