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59-402: Single-wire earth return ( SWER ) or single-wire ground return is a single-wire transmission line which supplies single-phase electric power from an electrical grid to remote areas at lowest cost. The earth (or sometimes a body of water) is used as the return path for the current, to avoid the need for a second wire (or neutral wire ) to act as a return path. Single-wire earth return

118-415: A long wire antenna , robbing the radiated power from the guided mode. If the propagation velocity can be reduced below the speed of light then the surrounding fields become evanescent , and are thus unable to propagate energy away from the area surrounding the wire. Goubau investigated the beneficial effect of a wire whose surface is structured (rather than an exact cylinder) such as would be obtained using

177-419: A voltaic cell (battery). He understood that such a current required a complete circuit to conduct the electricity, even though the actual nature of electric currents was not at all understood (only a century later would the electron be discovered). All subsequent development of electrical motors, lights, etc. relied on the principle of a complete circuit, generally involving a pair of wires, but sometimes using

236-422: 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. Many national electrical regulations (notably the U.S.) require a metallic return line from

295-444: A large power given a proper impedance match , as can be obtained through electrical resonance . This observation has been rediscovered several times, and described, for instance, in a 1993 patent. Single-wire transmission in this sense is not possible using direct current and totally impractical for low frequency alternating currents such as the standard 50–60 Hz power line frequencies. At much higher frequencies, however, it

354-541: A lightning strike. SWER is promoted as safe due to isolation of the ground from both the generator and user. Most other electrical systems use a metallic neutral connected directly to the generator or a shared ground. 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

413-480: A network of such lines, combined with coastal wind turbines , could substantially reduce rural Alaska's dependence on increasingly expensive diesel fuel for power generation. Alaska's state economic energy screening survey advocated further study of this option to use more of the state's underutilized power sources. At present, certain developing nations have adopted SWER systems as their mains electricity systems, notably Laos , South Africa and Mozambique . SWER

472-399: 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-up transformer at the head of the line, completing the circuit . SWER is therefore

531-544: A paper predicting the use of a single cylindrical conductor (wire) to propagate radio frequency energy as a surface wave . Sommerfeld's "wire wave" was of theoretical interest as a propagating mode, but this was decades before technology existed for the generation of sufficiently high radio frequencies for any such experimentation, let alone practical applications. What's more, the solution described an infinite transmission line without consideration of coupling energy into (or out of) it. Of particular practical interest, though,

590-476: A practical example of a phantom loop . In areas with higher-resistance soil, the grounding rod can float to higher voltages, wasting energy. The resistance may be high enough to affect self-resetting circuit breakers, which usually reset due to a difference in voltage between line and neutral. With dry, high-resistance soils, the reduced difference in voltage between line and neutral may prevent breakers from resetting. In Australia, locations with very dry soils need

649-420: A railway line). Wooden poles are acceptable. In Mozambique, poles had to be at least 12 m (39 ft) high to permit safe passage of giraffes beneath the lines. If an area is prone to lightning, modern designs place lightning ground straps in the poles when they are constructed, before erection. The straps and wiring can be arranged to be a low-cost lightning arrestor with rounded edges to avoid attracting

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708-465: A single-wire transmission line there is no second conductor of any form. As early as the 1780s Luigi Galvani first observed the effect of static electricity in causing the legs of a frog to twitch, and observed the same effect produced just due to certain metallic contacts with the frog involving a complete circuit. The latter effect was correctly understood by Alessandro Volta as an electric current inadvertently produced by what would become known as

767-424: 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. Most fire safety hazards in electrical distribution are from aging equipment: corroded lines, broken insulators, etc. The lower cost of SWER maintenance can reduce the cost of safe operation in these cases. SWER avoids lines clashing in wind,

826-533: A substantial fire-safety feature, but a problem surfaced in the official investigation into the Black Saturday bushfires in Victoria, Australia . These demonstrated that a broken SWER conductor can short to ground across a resistance similar to the circuit's normal load; in that particular case, a tree. This can cause large currents without a ground-fault indication. This can present a danger in fire-prone areas where

885-406: A threaded wire. More significantly, Goubau proposed the application of a dielectric layer surrounding the wire. Even a rather thin layer (relative to the wavelength) of a dielectric will reduce the propagation velocity sufficiently below the speed of light, eliminating radiation loss from a surface wave along the surface of a long straight wire. This modification also had the effect of greatly reducing

944-713: Is a 0.16-inch-diameter (4.064 mm) gauge of wire on the British Standard Wire Gauge that has entered into the cultural lexicon of New Zealand . Early farm fences in New Zealand were generally used to protect crops, gardens, and orchards from farm animals, rather than to contain the stock. Fencing methods used were post-and-rail fences, ditch-and-bank fences, stone walls, and hedges, but all proved too expensive to install and maintain to fence entire properties and tended to be unreliable. To prevent stock straying, boundary keepers were employed to patrol boundaries. In

1003-471: Is also used extensively in Brazil. Many high-voltage direct current systems (HVDC) using submarine power cables are single wire earth return systems. Bipolar systems with both positive and negative cables may also retain a seawater grounding electrode, used when one pole has failed. To avoid electrochemical corrosion, the ground electrodes of such systems are situated apart from the converter stations and not near

1062-482: Is high information rate channels using existing power lines for communications purposes. "Some ten years ago, I recognized the fact that to convey electric currents to a distance it was not at all necessary to employ a return wire, but that any amount of energy might be transmitted by using a single wire. I illustrated this principle by numerous experiments, which, at that time, excited considerable attention among scientific men." Number 8 wire Number 8 wire

1121-404: Is necessary to have a minimum of one half wave of conductor length to fully support the propagating mode. For these reasons, and at frequencies available prior to about 1950, the practical disadvantages of such transmission completely outweighed the reduced loss due to the wire's finite conductivity. In 1950 Georg Goubau revisited Sommerfeld's discovery of a surface wave mode along a wire, but with

1180-509: Is poor, and bushfire is a risk. Power is supplied to the SWER line by an isolating transformer of up to 300  kVA . This transformer isolates the grid from ground or earth. The voltage changes due to the transition from line-to-line to line-to-earth, typically reducing a 22 kV grid to 12.7 kV SWER or a 33 kV grid to 19.1 kV SWER. The SWER line is a single conductor that may stretch for tens or even hundreds of kilometres, with

1239-425: Is possible for the return circuit (which would normally be connected through a second wire) to utilize the self- and parasitic capacitance of a large conductive object, perhaps the housing of the load itself. Although the self-capacitance of even large objects is rather small in ordinary terms, as Tesla himself appreciated it is possible to resonate that capacitance using a sufficiently large inductor (depending on

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1298-637: Is principally used for rural electrification , but also finds use for larger isolated loads such as water pumps. It is also used for high-voltage direct current over submarine power cables . Electric single-phase railway traction, such as light rail , uses a very similar system. It uses resistors to earth to reduce hazards from rail voltages, but the primary return currents are through the rails. Lloyd Mandeno , OBE (1888–1973) fully developed SWER in New Zealand around 1925 for rural electrification. Although he termed it "Earth Working Single Wire Line", it

1357-579: Is used throughout the globe, most commonly in New Zealand and Australia. SWER systems are forbidden for national electric regulation RETIE (REGLAMENTO DE INSTALACIONES ELECTRICAS). In 1981 a high-power 8.5 mile prototype SWER line was successfully installed from a diesel plant in Bethel to Napakiak in Alaska , United States . It operates at 80 kV, and was originally installed on special lightweight fiberglass poles that formed an A-frame . Since then,

1416-469: The Baltic Cable and Kontek . The following table shows various installations of SWER systems Single-wire transmission line The single-wire transmission line is not the same as the single-wire earth return system, which is not covered in this article. The latter system relies on a return current through the ground , using the earth as a second conductor between ground terminal electrodes. In

1475-471: The 1850s, heavy annealed iron wire became available for fences, but this wire was very thick and only came in short lengths, was hard to work and to keep taut, and was expensive to use. In England, in 1855, Henry Bessemer patented the Bessemer process that led to the mass production of low-cost high-quality steel, leading to the large scale production of affordable lighter gauge steel wire. The introduction of

1534-465: The A frames have been removed and standard wooden power poles were installed. The A-framed poles could be carried on lightweight snow machines , and could be installed with hand tools on permafrost without extensive digging. Erection of "anchoring" poles still required heavy machinery, but the cost savings were dramatic. Researchers at the University of Alaska Fairbanks , United States estimate that

1593-628: The AIEE at Columbia College, N.Y.C., the IEE, London, the Franklin Institute, Philadelphia, and National Electric Light Association, St. Louis, it was shown that electric motors and single-terminal incandescent lamps can be operated through a single conductor without a return wire. Although apparently lacking a complete circuit, such a topology effectively obtains a return circuit by virtue of the load's self-capacitance and parasitic capacitance . Thus coils of

1652-508: The United States' Upper Midwest and Alaska ( Bethel ). SWER is a viable 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. SWER can cause fires when maintenance

1711-471: The base of a cone, with its narrow end connected typically to the shield of coaxial feed line , and the transmission line itself connecting to the center conductor of the coax. Even with the reduced extent of the surrounding fields in Goubau's design, such a device only becomes practical at UHF frequencies and above. With technological development at terahertz frequencies, where metallic losses are yet greater,

1770-451: 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 obsolete 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,

1829-457: 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

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1888-438: The footprint of the electromagnetic fields surrounding the wire, addressing the other practical concern. Finally, Goubau invented a method for launching (and receiving) electrical energy from such a transmission line. The patented Goubau line (or "G-line") consists of a single conductor coated with dielectric material. At each end is a wide disk with a hole in the center through which the transmission line passes. The disk may be

1947-458: The frequency used), in which case the large reactance of that capacitance is cancelled out. This allows a large current to flow (and a large power to be supplied to the load) without requiring an extremely high voltage source. Although this method of power transmission has long been understood, it is not clear whether there has been any commercial application of this principle for power transmission . As early as 1899, Arnold Sommerfeld published

2006-477: The ground as the second conductor (as with commercial telegraphy ). At the end of the 19th century, Nikola Tesla demonstrated that by using an electrical network tuned to resonance it was possible to transmit electric power using only a single conductor, with no need for a return wire. This was spoken of as the "transmission of electrical energy through one wire without return". In 1891, 1892, and 1893 demonstration lectures with electrical oscillators before

2065-405: 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 which can be measured using specialist earth test equipment. SWER systems are designed to limit the electric field in

2124-839: The grounding rods to be extra deep. Experience in Alaska shows that SWER needs to be grounded below permafrost , which is high-resistance. 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

2183-436: 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. It does also allow the use of a DC test loop, to distinguish a legitimate variable load from (for example) a fallen tree, which would be a DC path to ground. Single-wire earth return

2242-432: The intent of increasing its practicality. One major goal was to reduce the extent of the fields surrounding the conductor so that such a wire would not require an unreasonably large clearance. Another problem was that Sommerfeld's wave propagated exactly at the speed of light (or the slightly lower speed of light in air, for a wire surrounded by air). That meant that there would be radiation losses . The straight wire acts as

2301-475: 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 7 poles per kilometre (12 poles per mile), with spans of 100 to 150 metres (110 to 160 yards). SWER's high line voltage and low current also permits the use of low-cost galvanized steel wire (historically, No. 8 fence wire). Steel's greater strength permits spans of 400 metres (¼ mile) or more, reducing

2360-657: 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 bush fires. Since the bulk of the transmission line has low resistance attachments to earth, excessive ground currents from shorts and geomagnetic storms are more rare than in conventional metallic-return systems. So, SWER has fewer ground-fault circuit-breaker openings to interrupt service. A well-designed SWER line can be substantially upgraded as demand grows without new poles. The first step may be to replace

2419-473: The load to the generator. In these jurisdictions, each SWER line must be approved by exception. 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 30% of 3-wire three-phase systems. Maintenance costs are roughly 50% of an equivalent three phase line. SWER also reduces

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2478-496: 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. SWER lines tend to be long, with high impedance, so

2537-737: The long spans and high mechanical tensions, vibration from wind can cause damage to the wires. Modern systems install spiral vibration dampers on the wires. Insulators are often porcelain because polymers are prone to ultraviolet damage. Some utilities install higher-voltage insulators so the line can be easily upgraded to carry more power. For example, 12 kV lines may be insulated to 22 kV, or 19 kV lines to 33 kV. 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. In New Zealand, metal poles are common (often being former rails from

2596-424: The metric system , number 8 wire is officially referred to as 4.0 mm gauge wire, although the older term "Number 8 wire" continues to be commonly used. As a consequence of the ubiquitous use of number 8 wire in New Zealand, remote farms often had rolls of number 8 wire on hand, and the wire would often be used inventively and practically to solve mechanical or structural problems other than fencing. Accordingly,

2655-435: The new steel fencing wire of various gauges in the 1860s allowed the rapid construction of low-cost fencing and was quickly adopted for use on New Zealand sheep farms. Galvanised number 8 steel wire soon became the preferred standard. These new, lightweight steel wire fences were not suitable for cattle, as cattle would lean over or on the fences and damage or push the fences over. When barbed wire became available in 1879, it

2714-437: The number of poles to 2.5 per kilometre (4 per mile). 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. 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

2773-403: 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

2832-423: The presence of the wire acts to guide that wave toward the load, rather than radiating away. The reduction of ohmic losses compared to using coax (or other two-wire transmission lines) is especially an advantage at higher frequencies where these losses become very large. Practically speaking, use of this transmission mode below microwave frequencies is very problematic due to the very extended field patterns around

2891-407: The proper dimensions might be connected each with only one of its ends to the mains from a machine of low E. M. F., and though the circuit of the machine would not be closed in the ordinary acceptance of the term , yet the machine might be burned out if a proper resonance effect would be obtained. The final reference to "burning out" a machine was to emphasize the ability of such a system to transmit

2950-596: 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). Proper mechanical design of a SWER line can lower its lifetime cost and increase its safety. Since the line is high voltage, with small currents, the conductor used in historic SWER lines was Number-8 galvanized steel fence wire. More modern installations use specially-designed AS1222.1 high-carbon steel , aluminum-clad wires. Aluminum clad wires corrode in coastal areas, but are otherwise more suitable. Because of

3009-468: 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. 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

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3068-455: The term "number 8 wire" came to represent the ingenuity and resourcefulness of New Zealanders , and the phrase "a number 8 wire mentality" evolved to denote an ability to create or repair machinery using whatever scrap materials are available on hand. New Zealand hardware and DIY store franchise Mitre 10 have adopted "Number 8" as their in house brand for generic hardware supplies and tools. The Waikato Museum runs an art award named after

3127-467: The transmission cable. The electrodes can be situated in the sea or on land. Bare copper wires can be used for cathodes, and graphite rods buried in the ground, or titanium grids in the sea are used for anodes. To avoid electrochemical corrosion (and passivation of titanium surfaces) the current density at the surface of the electrodes must be small, and therefore large electrodes are required. Examples of HVDC systems with single wire earth return include

3186-458: The use of transmission using surface waves and Goubau lines appears promising. From 2003 through 2008 patents were filed for a system using Sommerfeld's original bare (uncoated) wire, but employing a launcher similar to that developed by Goubau. It was promoted under the name "E-Line" through 2009. This line is claimed to be completely non-radiating, propagating energy by a previously ignored transverse-magnetic (TM) wave. The intended application

3245-435: 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. After some years of experience, the inventor advocated a capacitor in series with the ground of the main isolation transformer to counteract

3304-421: The wire. The fields associated with the surface wave along the conductor are significant out to many conductor diameters, therefore metallic or even dielectric materials inadvertently present in these regions will distort the propagation of the mode and typically will increase propagation loss. Although there is no wavelength dependence to this dimension in the transverse direction, in the direction of propagation it

3363-537: Was often called "Mandeno’s Clothesline". More than 200,000 kilometres (100,000 miles) 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 around the world, such as in the Canadian province of Saskatchewan ; Brazil ; Africa ; and portions of

3422-431: Was the prediction of a substantially lower signal attenuation compared to using the same wire as the center conductor of a coaxial cable . Contrary to the previous explanation of the full transmitted power being due to a classical current through a wire, in this case the currents in the conductor itself are much smaller, with the energy transmitted in the form of an electromagnetic wave ( radio wave ). But in this case,

3481-463: Was used as the top wire and perhaps a lower additional wire in conjunction with No. 8 wire on fences on dairy and cattle farms to prevent the animals from damaging the fences. This further extended the use of number 8 wire. From the early 1960s, high-tensile 12½ gauge (2.5 mm) steel wire has largely replaced number 8 wire for New Zealand fencing, as it is lighter and cheaper, though also more difficult to work. Since 1976, when New Zealand adopted

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