# single wire transmission



## MDShunk

They use SWER transmission systems in parts of Western Australia, but that's about the only place I know of that it's used. No hope for 3-phase, however.


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## macmikeman

Single Wire Earth Return system. Still in use in Rural areas. Australia is a good place to find it. Known as "SWER".


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## Rap2

I have heard of such things and will google more in a minute. Forget 3 phase for a moment. If it were split phase would it be as simple as back feeding a 12Kv to 240v split phase transformer to another on the other side of the singe line to do the reverse?

It is a split phase system, I remember they have a motor control to kick out 3phase and run a well pump....


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## micromind

There is still quite a bit of SWER in northern Nevada, mostly old farms way out in the middle of nowhere. Some of these systems are more than 30 miles from anything.

It looks sort of strange to see a two-wire overhead single phase then only one wire tapped off and run at the top of a bunch of poles that disappear somewhere. 

"If the lights get dim, go pour some salt water down by the power pole."


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## McClary’s Electrical

*Single-wire earth return*

From Wikipedia, the free encyclopedia

Jump to: navigation, search 
 
Canadian SWER line


*Single wire earth return* (SWER) or *single wire ground return* is a single-wire transmission line for supplying single-phase electrical power from an electrical grid to remote areas at low cost. It is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps, and light rail. Single wire earth return is also used for HVDC over submarine power cables.

*[edit] Description*

SWER is a good choice for a distribution system when conventional return current wiring would cost more than SWER’s isolation transformers and small power losses. Power engineers experienced with both SWER and conventional power lines rate SWER as equally safe, more reliable, less costly, but with slightly lower efficiency than conventional lines.[1]

Power is supplied to the SWER line by an isolating transformer of up to 300kVa. This transformer isolates the grid from ground or earth, and changes the grid voltage (typically 22 kilovolts line to line) to the SWER voltage (typically 12.7 or 19.1 kilovolts line to earth).
The SWER line is a single conductor that may stretch for tens or even hundreds of kilometres, with a number of distribution transformers along its length. At each transformer, such as a customer's premises, current flows from the line, through the primary coil of a step-down isolation transformer, to earth through an earth stake. From the earth stake, the current eventually finds its way back to the main step-down transformer at the head of the line, completing the circuit.[1] SWER is therefore a practical example of a phantom loop.
In areas with high-resistance soil, SWER burns up grounding rods or may fail to reset breakers. In Australia, locations with very dry soils need the grounding rods to be extra deep.[2] Experience in Alaska shows that SWER needs to be grounded below permafrost, which is high-resistance.[3]
The secondary winding of the local transformer will supply the customer with either single ended single phase (N-0) or split phase (N-0-N) power in the region’s standard appliance voltages, with the 0 volt line connected to a safety earth that does not normally carry an operating current.
A large SWER line may feed as many as 80 distribution transformers. The transformers are usually rated at 5 kVA, 10 kVA and 25 kVA. The load densities are usually below 0.5 kVA per kilometer (0.8 kVA per mile) of line. Any single customer’s maximum demand will typically be less than 3.5 kVA, but larger loads up to the capacity of the distribution transformer can also be supplied.
Some SWER systems in the USA are conventional distribution feeders that were built without a continuous neutral (some of which were obsoleted transmission lines that were refitted for rural distribution service). The substation feeding such lines has a grounding rod on each pole within the substation; then on each branch from the line, the span between the pole next to and the pole carrying the transformer would have a grounded conductor (giving each transformer two grounding points for safety reasons).
*[edit] History*

At the end of the 19th century, Nikola Tesla demonstrated that only a single wire was necessary for power systems, with no need for a wired return conductor, using the Earth instead.[4] Lloyd Mandeno fully developed SWER in New Zealand around 1925 for rural electrification. Although he termed it “Earth Working Single Wire Line” it was often called “Mandeno’s Clothesline”. More than 200,000 kilometres have now been installed in Australia and New Zealand. It is considered safe, reliable and low cost, provided that safety features and earthing are correctly installed. The Australian standards are widely used and cited. It has been applied in the Canadian province of Saskatchewan, Brazil, Africa, portions of the United States' Upper Midwest, and SWER interties have been proposed for Alaska and prototyped.
*[edit] Characteristics*

*[edit] Safety*

SWER's safety is assured because transformers isolate the ground from both the generator and user. Most electrical systems use a metallic neutral connected directly to the generator or a shared ground. Certain groups claim that stray voltages from SWER can injure livestock.[1]
Grounding is critical. Significant currents on the order of 8 amperes flow through the ground near the earth points. A good-quality earth connection is needed to prevent risk of electric shock due to earth potential rise near this point. Separate grounds for power and safety are also used. Duplication of the ground points assures that the system is still safe if either of the grounds is damaged.
A good earth connection is normally a 6 m stake of copper-clad steel driven vertically into the ground, and bonded to the transformer earth and tank. A good ground resistance is 5–10 ohms. 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.
Other standard features include automatic reclosing circuit breakers (reclosers). Most faults (overcurrent) are transient. Since the network is rural, most of these faults will be cleared by the recloser. Each service site needs a rewirable drop out fuse for protection and switching of the transformer. The transformer secondary should also be protected by a standard high-rupture capacity (HRC) fuse or low voltage circuit breaker. A surge arrestor (spark gap) on the high voltage side is common, especially in lightning-prone areas.
The official investigation into the Black Saturday bushfires in Victoria, Australia, disclosed that a broken SWER conductor that comes in contact with a return path entry point with resistance similar to the circuit's normal load (such as a tree) can cause large amounts of current to flow to ground without a fault indication.[5] This presents a danger in fire-prone areas where a conductor may snap and current may arc through trees or dry grass.
Bare-wire or ground-return telecommunications can be compromised by the ground-return current if the grounding area is closer than 100 m or sinks more than 10 A of current. Modern radio, optic fibre channels and cell phone systems are unaffected.
*[edit] Cost advantage*

SWER’s main advantage is its low cost. It is often used in sparsely populated areas where the cost of building an isolated distribution line cannot be justified. Capital costs are roughly 50% of an equivalent two-wire single-phase line. They can cost 70% less than 3-wire three-phase systems. Maintenance costs are roughly 50% of an equivalent line.
SWER also reduces the largest cost of a distribution network, the number of poles. Conventional 2-wire or 3-wire distribution lines have a higher power transfer capacity, but can require seven poles per kilometre, with spans of 100 to 150 metres. SWER’s high line voltage and low current also permits the use of low-cost galvanized steel wire. Steel’s greater strength permits spans of 400 metres or more, reducing the number of poles to 2.5 per kilometre.
Reinforced concrete poles have been traditionally used in SWER lines because of their low cost, low maintenance, and resistance to water damage, termites and fungi. Local labor can produce them in most areas, further lowering costs.
If the poles also carry optical fiber cable for telecommunications (metal conductors may not be used), capital expenditures by the power company may be further reduced.
*[edit] Reliability strengths*

SWER can be used in a grid or loop, but is usually arranged in a linear or radial layout to save costs. In the customary linear form, a single-point failure in a SWER line causes all customers further down the line to lose power. However, since it has fewer components in the field, SWER has less to fail. For example, since there is only one line, winds can’t cause lines to clash, removing a source of damage, as well as a source of rural brush fires.
Since the line can't clash in the wind, and the bulk of the transmission line has low resistance attachments to earth, excessive ground currents from shorts and geomagnetic storms are far more rare than in conventional metallic-return systems. So, SWER has fewer ground-fault circuit-breaker openings to interrupt service.
*[edit] Power quality weakness*

SWER lines tend to be long, with high impedance, so the voltage drop along the line is often a problem, causing poor regulation. Variations in demand cause variation in the delivered voltage. To combat this, some installations have automatic variable transformers at the customer site to keep the received voltage within legal specifications.[6]
When used with distributed generation, SWER is substantially more efficient than when it is operated as a single-ended system. For example, some rural installations can offset line losses and charging currents with local solar power, wind power, small hydro or other local generation. This can be an excellent value for the electrical distributor, because it reduces the need for more lines.
After some years of experience, the inventor advocated a capacitor in series with the ground of the main isolation transformer to counteract the inductive reactance of the transformers, wire and earth return path. The plan was to improve the power factor, reduce losses and improve voltage performance due to reactive power flow.[1] Though theoretically sound, this is not standard practice.
*[edit] Networks and circuits*

As demand grows, a well-designed SWER line can be substantially upgraded without new poles.[7] The first step may be to replace the steel wire with more expensive copper-clad or aluminum-clad steel wire.
It may be possible to increase the voltage. Some distant SWER lines now operate at voltages as high as 35 kV. Normally this requires changing the insulators and transformers, but no new poles are needed.[8]
If more capacity is needed, a second SWER line can be run on the same poles to provide two SWER lines 180 degrees out of phase. This requires more insulators and wire, but doubles the power without doubling the poles. Many standard SWER poles have several bolt holes to support this upgrade. This configuration causes most ground currents to cancel, reducing shock hazards and interference with communication lines.
Two phase service is also possible with a two-wire upgrade: Though less reliable, it is more efficient. As more power is needed the lines can be upgraded to match the load, from single wire SWER to two wire, single phase and finally to three wire, three phase. This ensures a more efficient use of capital and makes the initial installation more affordable.
Customer equipment installed before these upgrades will all be single phase, and can be reused after the upgrade. If small amounts of three-phase power are needed, it can be economically synthesized from two-phase power with on-site equipment.


In 1981 a high-power 8.5 mile prototype SWER intertie was successfully installed from a coal plant in Bethel to Napakiak in Alaska, United States. It operates at 80 kV, and has special lightweight fiberglass poles forming an A-frame. The poles can be carried on lightweight snow machines, and most poles can be installed with hand tools on permafrost without extensive digging. Erection of “anchoring” poles still required heavy machinery, but the cost savings were dramatic.


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## Rap2

Well don't most split phase transformers use an earth ground to go from 12.47Kv(or whatever) to 240 split phase? I don't see why you couldn't back feed a PV system between 2 of them to get to the utility meter.


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## McClary’s Electrical

Rap2 said:


> Well don't most split phase transformers use an earth ground to go from 12.47Kv(or whatever) to 240 split phase? I don't see why you couldn't back feed a PV system between 2 of them to get to the utility meter.


 
On a side note, why is the PV system so far from the meter?, and can't you build another service closer and feed that? Efficiency and voltage drop are important to PV systems, and SWER is not the best when it comes to those aspects.


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## Wirenuting

mcclary's electrical said:


> On a side note, why is the PV system so far from the meter?, and can't you build another service closer and feed that? Efficiency and voltage drop are important to PV systems, and SWER is not the best when it comes to those aspects.


Is this the system / cause of a stray voltage issue that MH was discussing a few years ago. It was a question posed to Mike about dairy cows producing less milk.


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## den

I didn't read the whole explanation thing but this is done all the time. When we have an ice storm tornado etc. with a lot of peope off we would just put up the hot wire and leave the neutral down to be fixed later. This works ok because all the services are grounded good and the houses and out buildings are grounded (supposedly.) This could lead to some stray voltage if conditions are right but is rarely a problem around here. Our dairy's that had problems were just not gounded good at their buildings and service pannels. Animals can feel electric current at a low voltage ( some at 5 volts or lower) where we can't feel current until around 30 v. or so.


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## McClary’s Electrical

den said:


> I didn't read the whole explanation thing but this is done all the time. When we have an ice storm tornado etc. with a lot of peope off we would just put up the hot wire and leave the neutral down to be fixed later. This works ok because all the services are grounded good and the houses and out buildings are grounded (supposedly.) This could lead to some stray voltage if conditions are right but is rarely a problem around here. Our dairy's that had problems were just not gounded good at their buildings and service pannels. Animals can feel electric current at a low voltage ( some at 5 volts or lower) where we can't feel current until around 30 v. or so.


 

Very trure, I'm sure. But I think if you'd be honest about somethings you've witnessed as lineman, most of the temporary fixes they throw up in situations to get power back on , are many times dangerous. At least some of the stuff I see them do here during ice storms and such, it seems all regs. are thrown out window in those situations.


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## Wirenuting

den said:


> I didn't read the whole explanation thing but this is done all the time. When we have an ice storm tornado etc. with a lot of peope off we would just put up the hot wire and leave the neutral down to be fixed later. This works ok because all the services are grounded good and the houses and out buildings are grounded (supposedly.) This could lead to some stray voltage if conditions are right but is rarely a problem around here. Our dairy's that had problems were just not gounded good at their buildings and service pannels. Animals can feel electric current at a low voltage ( some at 5 volts or lower) where we can't feel current until around 30 v. or so.


Ok thank you. 
I was wondering about that one.


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## Rap2

mcclary's electrical said:


> On a side note, why is the PV system so far from the meter?, and can't you build another service closer and feed that? Efficiency and voltage drop are important to PV systems, and SWER is not the best when it comes to those aspects.



It can,t be closer because this PV installation it to offset the power drawn by a well pump which is about 1000' deep and somewhere around 60HP (or more I forget) it pumps water to the surface to another pump which sends it up to a holding tank a couple of miles away and yet another 500' higher.

All this is done on a very small easement of property, I would say 2000 square feet.

The land they want to use for the ground mount PV is 3/4 of a mile away in a very rocky terrain which is hard to dig a trench in.


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## Electric_Light

How much extra energy is lost to heating up the ground in resistive loss?


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## TOOL_5150

Electric_Light said:


> How much extra energy is lost to heating up the ground in resistive loss?


I suppose that depends on the length of the "run"

~Matt


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## Electric_Light

TOOL_5150 said:


> I suppose that depends on the length of the "run"
> 
> ~Matt


I suppose there's a figure for watts/ampere-feet?


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## randas

Just about everything outside city limits here is single wire transmission. Keeps the thieves off the transformer grounds :laughing:


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## Electric_Light

randas said:


> Just about everything outside city limits here is single wire transmission. Keeps the thieves off the transformer grounds :laughing:


So the transformer is like a microwave transformer that uses casing as return path? What safety precautions are in place to prevent hazardous potential difference between case and ground in the event the transformer is yanked off the ground, such as a truck backing into it, which happens pretty often with those cable TV junction stubs. (those 4" x 4" x 24" green things) ?


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## miller_elex

I don't like SWER, because if there was potentially a high resistance on the return path, an open-neutral if you will, it could put potentials in the kV's on your neutral in your house.

Seeing as metallic water pipe is bonded, it probably has alot of buried pipe and metal fences in the return current path. YIKES


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## joethemechanic

micromind said:


> There is still quite a bit of SWER in northern Nevada, mostly old farms way out in the middle of nowhere. Some of these systems are more than 30 miles from anything.
> 
> It looks sort of strange to see a two-wire overhead single phase then only one wire tapped off and run at the top of a bunch of poles that disappear somewhere.
> 
> "If the lights get dim, go pour some salt water down by the power pole."


I love that trick


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## joethemechanic

Electric_Light said:


> How much extra energy is lost to heating up the ground in resistive loss?


Not as much as you would think if the grounding systems are good. The earth is a good conductor because of it's large cross sectional area. And every time you double the voltage you quarter the I^2R heating. Many times the current is only a couple of amps in the primary side. In fact some systems use steel wire because of the low cost of materials, and the fact that you can increase pole spacing because of steel's greater tensile strength.


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## bobelectric

I think the lineman only does lineman stuff, not engineering.


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## Cletis

*Tramp Stamp*

I see you have a Tramp Stamp Fetish. 

You old, dirty, nasty, perverted man you...


I have the same problem


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## chicken steve

i wonder how the earthworm population fares on the swer 'return'

~CS~


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## Mshea

mcclary's electrical said:


> *Single-wire earth return*
> 
> From Wikipedia, the free encyclopedia
> 
> Jump to: navigation, search
> 
> Canadian SWER line
> 
> This photo looks exactly like a grounded return. The wire under the can is the grounded circuit conductor and it looks to be extended from pole to pole. Certainly would not assume a SWER from that photo.
> The early telegraph systems used SWER and as they added more and more wires to the poles people started to get killed working around poorly grounded returns. SWER is mostly used by utilities these days for HV transmission. There are still some in southern Alberta and I see some in Saskatchewan. They have no place in high population areas because they are dangerous, Australia's usage notwithstanding.
> Funny how the post starts by saying it is safe then lists all the unsafe conditions and problems with it.


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## chicken steve

well i can see how one tree branch could ruin the whole day.....~CS~


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