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Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line which supplies
single-phase electric power 173px, A single-phase polemount stepdown transformer in Canada. One supply phase (phase-to-neutral) from the utility is converted to split-phase for the customers. In electrical engineering, single-phase electric power is the distribution of alter ...
from an
electrical grid An electrical grid is an interconnected network for from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power Transmission: Backgr ...
to remote areas at low cost. Its distinguishing feature is that the
earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...
(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 As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equ ...
'') to act as a return path. Single-wire earth return is principally used for
rural electrification Rural electrification is the process of bringing electrical power Electric power is the rate, per unit time, at which electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
, but also finds use for larger isolated loads such as water pumps. It is also used for
high-voltage direct current A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
over
submarine power cable A submarine power cable is a transmission cable for carrying electric power Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt The watt (symbol: W) ...
s. Electric single-phase railway traction, such as
light rail Light rail transit (LRT) is a form of passenger urban rail transit Urban rail transit is an all-encompassing term for various types of local rail Rail or rails may refer to: Rail transport *Rail transport and related matters *Rail (rail t ...

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.


History

Lloyd Mandeno,
OBE The Most Excellent Order of the British Empire is a British order of chivalry An order of chivalry, order of knighthood, chivalric order, or equestrian order is an order of knights typically founded during or inspired by the original Cathol ...
(1888–1973) fully developed SWER in
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

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 Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

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 The provinces and territories of Canada () are sub-national divisions within the geographical areas of Canada under the jurisdiction of the Constitution of Canada, Canadian Constitution. In the 1867 Canadian Confederation, three provinces of Br ...
of
Saskatchewan ("From Many Peoples Strength") , image_map = Saskatchewan in Canada 2.svg , Label_map = yes , coordinates = , official_lang = English language, English , capital = Regina, S ...
;
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
;
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area and 20% of i ...

Africa
; and portions of the United States'
Upper Midwest The Upper Midwest is a region in the northern portion of the U.S. Census Bureau The United States Census Bureau (USCB), officially the Bureau of the Census, is a principal agency of the U.S. Federal Statistical System, responsible for produci ...
and
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, Anáaski) is a U.S. state in the Western United States, on the northwest extremity of the country's West Coast of the United State ...

Alaska
(
Bethel Bethel (Ugaritic Ugaritic () is an extinct , classified by some as a of the and so the only known Amorite dialect preserved in writing. It is known through the discovered by French in 1929 at , including several major literary texts, n ...
).


Operating principle

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 is poor, and bushfire is a risk. Power is supplied to the SWER line by an isolating
transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current in any one coil of the transformer produces a varying magnetic flux ...

transformer
of up to 300  kVA. This transformer isolates the grid from ground or earth, and changes the grid
voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

voltage
(typically 22 or 33 kV line-to-line) to the SWER voltage (typically 12.7 or 19.1 kV line-to-earth). The SWER line is a single
conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble like, for example, an orchestra. * Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of ...
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 Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...
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
circuitCircuit may refer to: Science and technology Electrical engineering * Electrical circuit, a complete electrical network with a closed-loop giving a return path for current ** Analog circuit, uses continuous signal levels ** Balanced circuit, p ...
. SWER is therefore a practical example of a
phantom loop In telecommunication and electrical engineering, a phantom circuit is an electrical circuit derived from suitably arranged wires with one or more conductive paths being a circuit in itself and at the same time acting as one conductor of another circ ...
. In areas with high-resistance soil, the resistance wastes energy. Another issue is that the resistance may be high enough that insufficient current flows into the earth neutral, causing the grounding rod to float to higher voltages. Self-resetting circuit breakers usually reset because of a difference in voltage between line and neutral. Therefore, 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 the grounding rods to be extra deep. Experience in Alaska shows that SWER needs to be grounded below
permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surfa ...

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 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).


Mechanical design

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 Carbon steel is a steel Steel is an alloy of iron with typically a few tenths of a percent of carbon to improve its strength of materials, strength and fracture toughness, fracture resistance compared to iron. Many other elements may be pres ...
, aluminum-clad wires. Aluminum clad wires corrode in coastal areas, but are otherwise more suitable.Power to the People
Describes use of SWER in the rural electrification of Mozambique. Transmission & Distribution World, 2009. Accessed 2011-8-10
Because of 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 Porcelain () is a ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant Corrosion is a Erosion, natural process that converts a refined metal into a more chemically stable form such as oxide, ...

porcelain
because polymers are prone to
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

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 Reinforced concrete (RC), also called reinforced cement concrete (RCC), is a composite material in which concrete's relatively low ultimate tensile strength, tensile strength and ductility are compensated for by the inclusion of reinforcement h ...
poles have been traditionally used in SWER lines because of their low cost, low maintenance, and resistance to water damage,
termite Termites are Eusociality, eusocial insects that are classified at the Taxonomy (biology), taxonomic rank of infraorder Isoptera, or alternatively as Taxonomic rank#All ranks, epifamily Termitoidae, within the order Blattodea (along with cockroa ...

termite
s and
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
. Local labor can produce them in most areas, further lowering costs. In New Zealand, metal poles are common (often being former rails from a railway line). Wooden poles are acceptable. In Mozambique, poles had to be at least high to permit safe passage of
giraffe The giraffe is a tall African mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''c ...

giraffe
s 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 a lightning strike.


Characteristics


Safety

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 
ampere The ampere (, ; symbol: A), often shortened to "amp",SI supports only the use of symbols and deprecates the use of abbreviations for units. is the base unit of electric current An electric current is a stream of charged particle In physics ...

ampere
s flow through the ground near the earth points. A good-quality earth connection is needed to prevent risk of
electric shock Electrical injury is a physiological reaction caused by electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature ...
due to
earth potential rise In electrical engineering, earth potential rise (EPR) also called ground potential rise (GPR) occurs when a large current flows to earth through an earth grid impedance. The potential relative to a distant point on the Earth is highest at the poi ...
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 which can be measured using specialist earth test equipment. SWER systems are designed to limit the electric field 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 (
recloser In electric power distribution, automatic circuit reclosers (ACRs) are a class of switchgear which is designed for use on overhead electricity distribution networks to detect and interrupt momentary Fault (power engineering), faults. Also known as ...
s). 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. 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, a substantial fire-safety feature, but a problem surfaced in the official investigation into the
Black Saturday bushfires The Black Saturday bushfires were a series of Bushfires in Australia, bushfires that either ignited or were already burning across the Australian state of Victoria (Australia), Victoria on and around Saturday, 7 February 2009, and were among Aus ...
in
Victoria, Australia Victoria (abbreviated as Vic) is a States and territories of Australia, state in southeastern Australia. It is the second-smallest state with a land area of and the most densely populated state in Australia (28 per km2). Victoria is bord ...
. 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 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 the load to the generator.''
National Electrical Code The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring Electrical wiring is an electrical Electricity is the set of physical phenomena associated with the pr ...
'' (NEC) (2008). Quincy, Mass. (USA)
National Fire Protection Association
In these jurisdictions, each SWER line must be approved by exception.


Cost advantages

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 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 7 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 Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc Zinc is a chemical element with the Symbol (chemistry), symbol Zn and atomic number 30. Zinc is a slightly brittle metal ...
wire (historically, No. 8 fence wire). Steel's greater strength permits spans of 400 metres or more, reducing the number of poles to 2.5 per kilometre. If the poles also carry
optical fiber cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...

optical fiber cable
for
telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical A cylinder (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Gr ...
s (metal conductors may not be used), capital expenditures by the power company may be further reduced.


Reliability

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 bush fires. Since the bulk of the transmission line has low resistance attachments to earth, excessive ground currents from shorts and
geomagnetic storm . Sizes are not to scale. A geomagnetic storm (commonly referred to as a solar storm) is a temporary disturbance of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth' ...
s are more rare than in conventional metallic-return systems. So, SWER has fewer ground-fault circuit-breaker openings to interrupt service.


Upgradeability

A well-designed SWER line can be substantially upgraded as demand grows without new poles. 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. 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 Three-phase electric power is a common method of alternating current electric power Electricity generation, generation, Electric power transmission, transmission, and Electric power distribution, distribution. It is a type of polyphase system and ...
are needed, it can be economically synthesized from two-phase power with on-site equipment.


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. After some years of experience, the inventor advocated a
capacitor A capacitor is a device that stores electric charge in an electric field An electric field (sometimes E-field) is the physical field that surrounds electrically-charged particle In physics Physics (from grc, φυσική (ἐπ ...

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 In electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics The field of electronics is a branch of ph ...
, reduce losses and improve voltage performance due to
reactive power Instantaneous power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude ...
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.


Use

In addition to New Zealand and Australia, single-wire earth return is used throughout the globe.


Alaska

In 1981 a high-power 8.5 mile prototype SWER line was successfully installed from a in
Bethel Bethel (Ugaritic Ugaritic () is an extinct , classified by some as a of the and so the only known Amorite dialect preserved in writing. It is known through the discovered by French in 1929 at , including several major literary texts, n ...
to Napakiak in
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, Anáaski) is a U.S. state in the Western United States, on the northwest extremity of the country's West Coast of the United State ...

Alaska
,
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
. It operates at 80 kV, and was originally installed on special lightweight
fiberglass Fiberglass (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Englis ...
poles that formed an . Since then, the A frames have been removed and standard wooden were installed. The A-framed poles could be carried on lightweight snow machines, and could be installed with hand tools on
permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surfa ...

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 The University of Alaska Fairbanks (UAF or Alaska) is a public In public relations Public relations (PR) is the practice of managing and disseminating information from an individual or an organization An organization, or organi ...
,
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
estimate that a network of such lines, combined with coastal
wind turbine A wind turbine is a device that converts Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination A religious denomination is a subgroup within a religion Religion is a social ...

wind turbine
s, could substantially reduce rural Alaska's dependence on increasingly expensive
diesel fuel Diesel fuel in general is any liquid fuel Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy In physical sciences Physical science is a branch of natural science that studies abi ...
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.


In developing nations

At present, certain developing nations have adopted SWER systems as their
mains electricity Mains electricity (Commonwealth English The use of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become ...
systems, notably
Laos , national_anthem = "Pheng Xat Lao "Pheng Sat Lāo" () is the national anthem A national anthem is a song that officially symbolizes a country A country is a distinct territory, territorial body or political entity. It is often r ...

Laos
,
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. With over 60 million people, it is the world's 23rd-most populous nation and covers an area of . South Africa has three capital citie ...

South Africa
and
Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in Southeastern Africa bordered by the Indian Ocean The Indian Ocean is the third-lar ...

Mozambique
. SWER is also used extensively in Brazil.


In HVDC systems

Many
high-voltage direct current A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
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 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 the
Baltic Cable The Baltic Cable is a monopolar HVDC power line An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy Electrical energy is energy derived from electric potential energy ...
and
Kontek The Kontek HVDC is a long, monopolar 400 kV high-voltage direct current A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy ...
.


References


External links


Rural power.org
Excellent site on this topic. Provides the PDF of Mandeno's article.
Manual for Single Wire Earth Return Power Systems
From the Network Power Standards Branch of the Australian Northern Territory Government. Includes dimensioned mechanical drawings and parts lists.
AS2558-2006 Transformers for use on single-wire earth-return distribution systems
- An Australian standard
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): 1002–101

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