Single wire earth return (SWER) or single wire ground return is a single-wire transmission line for supplying single-phase electrical power 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. A single-wire transmission line (or single wire method) is a method of supplying electrical power through a single wired electrical conductor. ... In electrical engineering, single-phase electric power refers to the distribution of electric power using a system in which all the voltages of the supply vary in unison. ... Transmission lines in Lund, Sweden Electric power, often known as power or electricity, involves the production and delivery of electrical energy in sufficient quantities to operate domestic appliances, office equipment, industrial machinery and provide sufficient energy for both domestic and commercial lighting, heating, cooking and industrial processes. ... Rural electrification is the process of bringing electrical power to rural and remote areas. ... This article is about light rail systems in general. ... HVDC or high-voltage, direct current electric power transmission systems contrast with the more common alternating-current systems as a means for the bulk transmission of electrical power. ... Submarine power cables are cables for electrical power running through the sea, below the surface. ...

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 300 kVA, this 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). Image File history File links Swer. ... Three-phase pole-mounted step-down transformer. ... now. ...

The SWER line is a single conductor that may stretch for tens or even hundreds of kilometres, visiting a number of termination points. At each termination point, such as a customer's premises, current flows from the line, through the primary coil of a step-down 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. SWER is therefore a practical example of a phantom loop. In science and engineering, conductors are materials that contain movable charges of electricity. ... km redirects here. ... Ground symbols The term ground or earth usually means a common return path in electrical circuits. ... An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ... A phantom loop is an electrical network that uses part of the natural environment to complete a circuit. ...

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 split phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial (up to about 100 kVA) applications. ...

A large SWER line may feed as many as 80 distribution transformers. Since the distribution system must carry reactive power (vars), as well as real power (watts), capacities are measured in volt-amperes, not watts. The transformers are usually rated at 5 kVA, 10 kVA and 25 kVA. The load densities are usually below 0.5 kVA per kilometer (0.31 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. Reactive power is an abstract quantity, typically used by power engineers to describe a certain type of energy flow in an electric distribution system. ... In the United States the term (Volt-amps) in Electrical terms, means watts. ... The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ...

History

At the end of the 19th century, Nikola Tesla demonstrated a single wire was necessary for power systems, with no need for a wired return conductor (using the Earth instead).^[2] 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 Saskatchewan, Brazil and Africa, and SWER interties have been proposed for Alaska and prototyped. Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ... A single-wire transmission line (or single wire method) is a method of supplying electrical power through a single wired electrical conductor. ... 1925 (MCMXXV) was a common year starting on Thursday (link will take you to calendar). ...

Safety

SWER violates common wisdom about electrical safety, because it lacks a traditional metallic return to a neutral shared by the generator. SWER's safety is instead assured because transformers isolate the ground from both the generator and user.

However, grounding is critical. Significant currents (of the order of 8 amperes) flow through the ground near the earth point, so a good-quality earth connection is needed to prevent risk of electric shock near this point. Separate grounds for power and safety are also used. Duplication of the grounds assures that the system is still safe if either of the grounds are damaged. A multimeter can be used to measure current The ampere (symbol: A) is the SI base unit of electric current. ... The term ground (or earth) usually means a common return in circuits. ... Sign warning of possible electric shock hazard An electric shock can occur upon contact of a human or animal body with any source of voltage high enough to cause sufficient current flow through the muscles or nerves. ...

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.

Other standard features include automatic reclosing circuit breakers (reclosers). Most faults (over current) 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. An autorecloser is a circuit breaker equipped with a mechanism that can automatically close the breaker after it has been opened due to a fault. ...

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.

Low cost: the main 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 be 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 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's high line voltage and low current permits the use of low-cost galvanized steel wire. Steel's greater strength permits spans of 400 m or more, reducing the number of poles to 2.5/km. Hot-dip galvanizing is the process of coating iron or steel with a thin zinc layer by passing the steel through a molten bath of zinc at a temperature of around 460°C. Zinc rusts to form zinc oxide, a fairly strong material that stops further rusting, protecting the steel...

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. Reinforced concrete at Sainte Jeanne dArc Church (Nice, France): architect Jacques Dror, 1926–1933 Reinforced concrete, also called ferroconcrete in some countries, is concrete in which reinforcement bars (rebars) or fibers have been incorporated to strengthen the material that would otherwise be brittle. ... Families Mastotermitidae Kalotermitidae Termopsidae Hodotermitidae Rhinotermitidae Serritermitidae Termitidae Reference: Earthlife as of 2002-07-26 A termite (also known as a white ant) is any member of the order Isoptera, a group of social insects that eat wood and other cellulose-rich vegetable matter. ... Divisions Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Deuteromycota The fungi (singular fungus) are a kingdom of eukaryotic organisms. ...

If the cable contains optic fibre ^[3], or carries RF phone line service, this can further amortize the capital costs. For other uses of Amortization, see the Amortization disambiguation page. ...

Reliability: a strength

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.

Power quality: a weakness

SWER lines tend to be long, with high impedance, so the voltage drop along the line is often a problem, causing poor power quality. 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.

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. (Kashem and Ledwich) Distributed generation is a new trend in electric power generation. ... Solar power describes a number of methods of harnessing energy from the light of the sun. ... Wind farm in Neuenkirchen, Dithmarschen, Germany. ... Micro hydro in North-West Vietnam Small hydro is the application of hydroelectric power on a commercial scale serving a small community or medium sized industry. ...

After some years of experience, the inventor (Mandeno, below) 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. Though theoretically sound, this is not standard practice. Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power. ... Reactive power is an abstract quantity, typically used by power engineers to describe a certain type of energy flow in an electric distribution system. ...

Upgrading a SWER line

Transformers need not be permanently installed. It is perfectly possible to place maximum-indicating thermometers in them, and install larger transformers as needed, moving the smaller ones to other positions.

As demand grows, a well-designed SWER line can be substantially upgraded without new poles. The first step may be to replace the steel wire with more expensive copper-clad or aluminum-clad steel wire.

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 wirelines.

Conventional two phase service is also possible with a two-wire upgrade: Though less reliable, it is more efficient and conforms to standard distribution practices. 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. Two-phase electrical power was used in some early 20th century factories and the distribution systems that served them. ...

Customer equipment installed before these upgrades will all be single phase, and can be reused after the upgrade. If moderate amounts of three-phase are needed, it can be economically synthesized from two-phase with on-site equipment. Three-phase power transformer which is the sole transfer point for electricity to a suburban shopping mall in Canada. ...

Use in interties

In 1981 a high-power 8.5 mile prototype SWER intertie was successfully installed from a coal plant in Bethel, Alaska to Napakiak, Alaska. It operates at 80 kV, and has special lightweight fiberglass poles that form 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. Bethel is a city located in Bethel Census Area, Alaska 340 miles west of Anchorage. ... Napakiak is a city located in Bethel Census Area, Alaska. ...

The phase conductor also carries a bundle of optic fibres within the steel armor wire ^[4] , so the system supplies telecommunications as well as power.

Researchers at the University of Fairbanks estimate that a network of such interties, combined with coastal wind turbines, could substantially reduce Alaska's dependence on increasingly expensive diesel fuel for power generation. ^[5] Alaska's state economic energy screening survey advocated further study of this option, in order to use more of the state's underutilized power sources. ^[6] Wind turbine in Luxembourg Horizontal axis wind turbine, the Enercon model E-66 wind energy converter, in Germany. ...

Regulatory issues

Many national electrical regulations (notably the U.S.) require a metallic return line from the load to the generator. In these jurisdictions, each SWER line must be approved by exception.

Use for HVDC systems

Many HVDC systems using submarine power cables are (or were until their expansion to bipolar schemes) single wire earth return systems. In order to avoid electrochemical corrosion, the ground electrodes of such systems are situated apart from the converter stations and not in the proximity of the transmission cable. The electrodes can be situated in the sea or on land. As cathodes, bare copper wires can be used in the sea or on land. As anodes, graphite rods dug in the ground, or titanium grids in the sea are used. In order to avoid electrochemical corrosion (and passivation of titanium surfaces) the current density at the surface of the electrodes may be only small and therefore large electrodes are required. 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. Submarine power cables are cables for electrical power running through the sea, below the surface. ...

Examples of HVDC systems with single wire earth return

• Baltic-Cable
• Kontek

The Baltic Cable is a HVDC power line running beneath the Baltic Sea that interconnects the electric power grids of Germany and Sweden. ... Kontek is a HVDC cable coupling the German and the Danish power grids. ...

References and notes

Citations

1. ^ Rural Power Supply Especially in Back Country Areas, L Mandeno, B.E., M.I.E.E. Proceedings of the New Zealand Institute of Engineers, 1947, Volume 33, Page 234.
2. ^ "Why did Tesla make his coil in the first place? What was it that he was trying to accomplish? Other than just the fun of making one, do they have any practical purposes?", tfcbooks.com.
3. ^ alcatel.com, custsolutionspowerlinesus.pdf
4. ^ alcatel.com custsolutionspowerlinesus.pdf
5. ^ uaf.edu singlewiregroundreturn.pdf
6. ^ dced.state.ak.us AIDEA_Energy_Screening.pdf

External articles and links

Websites

• "When One Wire Is Enough", Neil Chapman, Transmission & Distribution World, 2001

Other

Please use these lightly to avoid traffic on the servers and long-haul backbones, some of which are quite remote from the U.S. and Europe.

• Rural power.org; Contains "Rural Power Supply Especially in Back Country Areas", 7 megabyte scanned PDF
• Manual for Single Wire Earth Return Power Systems From the Network Power Standards Branch of the Australian Government. Includes dimensioned mechanical drawings and parts lists.
• AS2558-2006, Transformers for use on Single Wire Earth-Return Distribution Systems- An Australian standard
• Stone Power AB discusses low cost networks
• Saskatchewan in Canada has operated SWER for more than fifty years
• Distributed generation as voltage support for single wire earth return systems, Kashem, M.A.; Ledwich, G.; IEEE Transactions on Power Delivery, Volume 19, Issue 3, July 2004 Page(s): 1002 - 1011 [1]