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'{{Multiple issues| {{Refimprove|date=June 2014}} {{More footnotes|date= September 2014}} }} [[File:Polemount-singlephase-closeup.jpg|thumb|199px|A 50&nbsp;kVA pole-mounted distribution transformer]] An '''electric power distribution system''' is the final stage in the [[power delivery|delivery]] of [[electric power]]; it carries electricity from the [[electric power transmission|transmission system]] to individual consumers. Distribution substations connect to the [[electric power transmission|transmission system]] and lower the transmission voltage to medium [[voltage]] ranging between 2&nbsp;[[kilovolt|kV]] and 35&nbsp;kV with the use of [[transformer]]s. ''Primary'' distribution lines carry this medium voltage power to [[distribution transformer]]s located near the customer's premises. Distribution transformers again lower the voltage to the [[utilization voltage]] of household appliances and typically feed several customers through ''secondary'' distribution lines at this voltage. Commercial and residential customers are connected to the secondary distribution lines through [[service drop]]s. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the [[subtransmission]] level. ==History== {{further|History of electric power transmission}} [[File:Brush Company arc light madison square new york 1882.png|thumbnail|right|The late 1870s/early 1880s saw the introduction of [[arc lamp]] lighting used outdoors or in large indoor spaces such as this [[Brush Electric Company]] system installed in 1880 in [[New York City]].]] Electric power distribution only became necessary in the 1880s when electricity started being generated at [[power stations]]. Before that electricity was usually generated where it was used. The first power distribution systems installed in European and US cites were used to supply lighting: [[arc lamp|arc lighting]] running on very high voltage (usually higher than 3000 volt) [[alternating current]] (AC) or [[direct current]] (DC), and [[incandescent lamp|incandescent lighting]] running on low voltage (100 volt) direct current.<ref>Quentin R. Skrabec, The 100 Most Significant Events in American Business: An Encyclopedia, ABC-CLIO - 2012, page 86</ref> Both were supplanting [[gas lighting]] systems, with arc lighting taking over large area/street lighting, and incandescent lighting replacing gas for business and residential lighting. Due to the high voltages used in arc lighting, a single generating station could supply a long string of lights, up to {{convert|7|mi|km|adj=on}} long circuits,<ref>{{cite journal|journal=Journal of the Society of Telegraph Engineers|last=Berly|first=J.|publisher=Institution of Electrical Engineers|volume=IX|date=1880-03-24|title=Notes on the Jablochkoff System of Electric Lighting|url=http://books.google.com/?id=lww4AAAAMAAJ&pg=PA143|issue=32|page=143|accessdate=2009-01-07}}</ref> since the capacity of a wire is proportional to the square of the current traveling on it, each doubling of the voltage would allow the same size cable to transmit the same amount of power four times the distance. Direct current indoor incandescent lighting systems (for example the first Edison [[Pearl Street Station]] installed in 1882), had difficulty supplying customers more than a mile away due to the low 110 volt system being used throughout the system, from the generators to the final use. The Edison DC system needed thick copper conductor cables, and the generating plants needed to be within about {{convert|1.5|mi|km}} of the farthest customer to avoid excessively large and expensive conductors. === Introduction of the AC transformer === Trying to deliver electricity long distance at high voltage and then reducing it to a fractional voltage for indoor lighting became a recognized engineering roadblock to electric power distribution with many, not very satisfactory, solutions tested by lighting companies. The mid-1880s saw a breakthrough with the development of functional AC [[transformer]]s that allowed the voltage to be "stepped up" to much higher transmission voltages and then dropped down to a lower end user voltage. With much cheaper transmission costs and the greater [[economies of scale]] of having large generating plants supply whole cities and regions, the use of AC spread rapidly. In the US the competition between direct current and alternating current took a personal turn in the late 1880s in the form of a "[[War of Currents]]" when [[Thomas Edison]] started attacking [[George Westinghouse]] and his development of the first US AC transformer systems, pointing out all the deaths caused by high voltage AC systems over the years and claiming any AC system was inherently dangerous.<ref>{{cite book|first=Webb B.|last=Garrison|title=Behind the headlines: American history's schemes, scandals, and escapades|publisher=Stackpole Books|year=1983|page=107}}</ref> Edison's propaganda campaign was short lived with his company switching over to AC in 1892. AC became the dominant form of transmission of power with innovations in Europe and the US in [[electric motor]] designs and the development of engineered ''universal systems'' allowing the large number of legacy systems to be connected to large AC grids.<ref name="Thomas Parke Hughes 1930, pages 120-121">{{cite book|first=Thomas |last=Parke Hughes|title=Networks of Power: Electrification in Western Society, 1880-1930|publisher=JHU Press|year=1993|pages= 120-121}}</ref><ref name="Raghu Garud 2009, page 249">{{cite book|first1=Raghu|last1=Garud|first2=Arun|last2=Kumaraswamy|first3= Richard|last3= Langlois|title= Managing in the Modular Age: Architectures, Networks, and Organizations|publisher= John Wiley & Sons |year= 2009| page= 249}}</ref> In the first half of the 20th century, the [[electric power industry]] was [[vertical integration|vertically integrated]], meaning they one company did generation, transmission, distribution, and metering and billing. Starting in the 1970s and 1980s nations began the process of [[deregulation]] and [[privatisation]], leading to [[electricity market]]s. The distribution system would remain regulated, but generation, retail, and sometimes transmission systems were transformed into competitive markets. ==Generation and transmission== <imagemap> File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC [[electricity delivery]] from generation stations to consumers' [[service drop]]. rect 2 243 235 438 [[Power station]] rect 276 317 412 556 [[Transformer]] rect 412 121 781 400 [[Electric power transmission]] rect 800 0 980 165 [[Transformer]] desc bottom-left </imagemap>Electric power begins at a generating station, where the potential difference can be as high as 13,800&nbsp;volts.<ref name="parcours">{{Cite web|url=http://www.hydroquebec.com/learning/transport/parcours.html|title=Power Transmission and Distribution {{!}} Hydro-Québec|website=www.hydroquebec.com|access-date=2016-03-08}}</ref> AC is usually used. Users of large amounts of DC power such as some [[railway electrification system]]s, [[telephone exchange]]s and industrial processes such as [[aluminium]] smelting usually either operate their own or have adjacent dedicated generating equipment, or use rectifiers to derive DC from the public AC supply. However, [[HVDC|High-voltage DC]] can be advantageous for isolating alternating-current systems or controlling the quantity of electricity transmitted. For example, [[Hydro-Québec]] has a direct-current line which goes from the [[James Bay]] region to [[Boston]].<ref>{{Cite web|url=http://www.hydroquebec.com/learning/transport/grandes-distances.html|title=Extra-High-Voltage Transmission {{!}} 735 kV {{!}} Hydro-Québec|website=www.hydroquebec.com|access-date=2016-03-08}}</ref> From the generating station it goes to the generating station’s switchyard where a step-up [[transformer]]&nbsp;increases the voltage to a level suitable for transmission, from 44,000 to 765,000 volts. Once in the transmission system, electricity from each generating station is combined with electricity produced elsewhere. Electricity is consumed as soon as it is produced. It is transmitted at a very high speed, close to the [[speed of light]]. == Distribution == {{refimprove section|date=October 2014}}[[File:Electricity Grid Schematic English.svg|thumb|right|300px|General layout of [[grid (electricity)|electricity networks]]. The voltages and loadings are typical of a European network.]]The transition from transmission to distribution happens in a power [[Electrical substation|substation]], which has the the following fuctions:<ref>{{Cite web|url=http://science.howstuffworks.com/environmental/energy/power5.htm|title=How Power Grids Work|website=HowStuffWorks|access-date=2016-03-18}}</ref> * Circuit breakers and switches enable the substation to be disconnected from the transmission grid or for distribution lines to be disconnected. * Transformers step down transmission voltages, 35kV or more, down to primary distribution voltages. These are medium voltage circuits, usually 600-35,000 V. * From the transformer, power goes to the [[busbar]] that can split the distribution power off in multiple directions. The bus distributes power to distribution lines, which fan out to customers. Closer to the customer, a distribution transformer steps the primary distribution power down to a low-voltage secondary circuit, usually 120 or 240V, depending on the region. The electricity passes through cables which are suspended from&nbsp;towers to source substations, which lower the voltage, and then reaches the&nbsp;satellite substation<nowiki/>s, which further reduce the voltage<ref name="parcours" /> to about 25000 volts.<ref>{{Cite web|url=http://www.hydroquebec.com/learning/distribution/voie-aerienne.html|title=Overhead Distribution Lines {{!}} Hydro-Québec|website=www.hydroquebec.com|access-date=2016-03-08}}</ref> From there the electricity goes nearer to where it will be used via overhead lines where&nbsp;transformers attached to poles lower the voltage one last time, and then via [[service drop]] and an [[Electricity meter]] to houses. Conductors for distribution may be carried on overhead pole lines, or in densely populated areas, buried underground. Urban and suburban distribution is done with [[Three-phase electric power|three-phase]] systems to serve both residential, commercial, and industrial loads. Within these networks there may be a mix of overhead line construction utilizing traditional [[utility pole]]s and wires and, increasingly, underground construction with cables and indoor or cabinet substations. However, underground distribution is significantly more expensive than overhead construction. In part to reduce this cost, underground power lines are sometimes co-located with other utility lines in what are called [[common utility duct]]s. Distribution feeders emanating from a substation are generally controlled by a [[circuit breaker]] which will open when a fault is detected. Automatic circuit reclosers may be installed to further segregate the feeder thus minimizing the impact of faults. Voltage varies according to its role in the supply and distribution system. According to international standards, there are initially two voltage groups: low voltage (LV): up to and including 1,000 V AC (or 1,500 V DC) and high voltage (HV): above 1 kV AC (or 1.5 kV DC).<ref>{{Cite book|title=Planning of Electric Power Distribution|last=|first=|publisher=Siemens|year=2015|isbn=|location=https://w3.siemens.com/powerdistribution/global/EN/consultant-support/download-center/tabcardpages/Documents/Planning-Manuals/Planning_of_Electric_Power_Distribution_Technical_Principles.pdf|pages=}}</ref> Distribution voltages are 22kV or 11 kV.<ref name="eolss">{{cite book|last1=Chan|first1=F|title=Electrical Engineering|url=http://www.eolss.net/sample-chapters/c05/e6-39a-06-01.pdf|accessdate=12 March 2016|chapter=Electric Power Distribution Systems}}</ref> Only large consumers are fed directly from distribution voltages; most utility customers are connected to a transformer, which reduces the distribution voltage to the low voltage used by lighting and interior wiring systems. Electricity is delivered to at a frequency of either 50 or 60&nbsp;Hz, depending on the region. It is delivered to domestic customers as [[Single-phase electric power|single-phase electric power]]. Seen in an [[oscilloscope]], the domestic power supply in North America would look like a [[sine wave]], oscillating between -170 volts and 170 volts. The peaks are indeed 170 volts, giving an effective voltage of 120 volts.<ref>{{Cite web|url=http://science.howstuffworks.com/environmental/energy/power2.htm|title=How Power Grids Work|website=HowStuffWorks|access-date=2016-03-18}}</ref> [[Three-phase electric power|Three-phase]] power is more efficient in terms of power delivered per cable used, and is more suited to running large electric motors. Some large European appliances may be powered by three-phase power, such as electric stoves and clothes dryers. A [[Ground (electricity)|ground]] connection is normally provided for the customer's system as well as for the equipment owned by the utility. The purpose of connecting the customer's system to ground is to limit the voltage that may develop if high voltage conductors fall down onto lower-voltage conductors which are usually mounted lower to the ground, or if a failure occurs within a distribution transformer. [[Earthing system]]s can be TT, TN-S, TN-C-S or TN-C. ===Rural services=== {{Main| Rural electrification}} [[Rural electrification]] systems, in contrast to urban systems, tend to use higher distribution voltages because of the longer distances covered by distribution lines (see [[Rural Electrification Administration]]). 7.2, 12.47, 25, and 34.5&nbsp;kV distribution is common in the United States; 11&nbsp;kV and 33&nbsp;kV are common in the UK, Australia and New Zealand; 11&nbsp;kV and 22&nbsp;kV are common in South Africa. Other voltages are occasionally used. Distribution in rural areas may be only single-phase if it is not economical to install three-phase power for relatively few and small customers. Rural services normally try to minimize the number of poles and wires. [[Single-wire earth return]] (SWER) is the least expensive, with one wire. It uses higher voltages (than urban distribution), which in turn permits use of galvanized steel wire. The strong steel wire allows for less expensive wide pole spacing. In rural areas a pole-mount transformer may serve only one customer. Higher voltage split-phase or three phase service, at a higher infrastructure and a higher cost, provide increased equipment efficiency and lower energy cost for large agricultural facilities, petroleum pumping facilities, or water plants. In [[New Zealand]], [[Australia]], [[Saskatchewan|Saskatchewan, Canada]], and [[South Africa]], [[single wire earth return]] systems (SWER) are used to electrify remote rural areas. === Regional variations === {{refimprove section|date=October 2014}} [[image:Voltage and frequency.png|thumb|Worldwide electrical voltage and frequency.]] Many areas in the world use single-phase 220 V or 230 V residential and light industrial service. In this system, the high voltage distribution network supplies a few substations per area, and the 230 V power from each substation is directly distributed. A live (hot) wire and neutral are connected to the building from one phase of three phase service. Single-phase distribution is used where motor loads are light. ==== The Americas vs. Europe ==== Many countries in north, central and South America use 60&nbsp;Hz AC, the 120/240 volt [[split phase]] system is used domestically and three phase is used for larger installations. In Europe, electricity is normally distributed for industry and domestic use by the three-phase, four wire system. This gives a three-phase voltage of {{nowrap|400 volts}} wye service and a single-phase voltage of {{nowrap|230 volts}}. For industrial customers, 3-phase {{nowrap|690 / 400 volt}} is also available.{{citation needed|date=November 2011}}. Large industrial customers have their own transformers with an input from 10 kV to 220 kV. North American and European power distribution systems differ in that North American systems tend to have a greater number of low-voltage step-down transformers located close to customers' premises. For example, in the US a pole-mounted transformer in a suburban setting may supply 7-11 houses,{{citation needed|date=January 2013}} whereas in the UK a typical urban or suburban low-voltage substation would normally be rated between 315&nbsp;kVA and 1&nbsp;MVA and supply a whole neighborhood. This is because the higher domestic voltage used in Europe (230&nbsp;V vs 120&nbsp;V) may be carried over a greater distance with acceptable power loss. An advantage of the North American system is that failure or maintenance on a single transformer will only affect a few customers. Advantages of the UK system are that the transformers are fewer in number, larger and more efficient, and due to the diversity of many loads there is reduced waste due to there being less need for spare capacity in the transformers. In North American city areas with many customers per unit area, network distribution may be used, with multiple transformers interconnected with low voltage distribution buses over several city blocks. In many areas, "delta" three phase service is common. Delta service has no distributed neutral wire and is therefore less expensive. In North America and Latin America, three phase service is often a ''Y'' (''wye'') in which the neutral is grounded at various points. The neutral provides a low-resistance metallic return to the distribution transformer. Wye service is recognizable when a line has four conductors, one of which is lightly insulated. Three-phase wye service is ideal for motors and heavy power usage. ==== Japan ==== [[Image:Power Grid of Japan.svg|right|thumb|Japan's utility frequencies are {{nowrap|50 Hz}} and {{nowrap|60 Hz}}]]In the [[electricity sector in Japan]], the standard frequencies for AC are 50 and 60 Hz. Most countries are standardized on 50 Hz as. South Korea and most of the Americas, including the United States and Canada, use 60 Hz. In Japan, however, parts of the country use 50 Hz, while other parts use 60 Hz.<ref name=":1">{{Cite news|url=http://www.japantimes.co.jp/news/2011/07/19/reference/japans-incompatible-power-grids/|title=Japan’s incompatible power grids|last=Gordenker|first=Alice|date=2011-07-19|newspaper=The Japan Times Online|language=en-US|issn=0447-5763|access-date=2016-03-12}}</ref> This is a relic of the 1800s. Some local providers in [[Tokyo]] imported 50 Hz German equipment, while the local power providers in [[Osaka]] brought in 60 Hz generators from the United States. The grids grew until eventually the entire country was wired. Today the frequency is 50 Hz in Eastern Japan (including&nbsp;Tokyo,&nbsp;[[Yokohama]],&nbsp;[[Tōhoku region|Tohoku]], and [[Hokkaido]]) and 60 Hertz in Western Japan (including&nbsp;[[Nagoya]],&nbsp;[[Osaka]],&nbsp;[[Kyoto]],&nbsp;[[Hiroshima]],&nbsp;[[Shikokuchūō|Shikoku]], and [[Kyushu]]).<ref>{{Cite web|url=http://www.japan-guide.com/e/e2225.html|title=Electricity in Japan|website=www.japan-guide.com|access-date=2016-03-12}}</ref> Most household appliances are made to work on either frequency. The problem of incompatibility came into the public eye when the [[2011 Tōhoku earthquake and tsunami]] knocked out about a third of the east’s capacity, and power in the west couldn’t be fully shared with the east, since the country does not have a common frequency.<ref name=":1" /> There are four converter stations that move power across Japan’s AC frequency border. [[Shin Shinano]] is a [[Back-to-back connection#Power transmission|back-to-back]] HVDC facility in [[Japan]] which forms one of four [[frequency changer]] stations that link Japan's western and eastern power grids. The other three are at [[Higashi-Shimizu Frequency Converter|Higashi-Shimizu]], [[Minami-Fukumitsu]] and [[Sakuma Dam#HVDC frequency converter|Sakuma Dam]]. Together they can move up to 1.2 GW of power east or west.<ref>{{Cite web|url=http://spectrum.ieee.org/energy/the-smarter-grid/why-japans-fragmented-grid-cant-cope|title=Why Japan's Fragmented Grid Can't Cope|website=spectrum.ieee.org|access-date=2016-03-12}}</ref> == Distribution network configurations == [[File:NCPC Power Plant Yellowknife Northwest Territories Canada 08.jpg|thumb|Substation near [[Yellowknife]], in the Northwest Territories of Canada]] Distribution networks are divided into two types, radial or network.<ref>{{cite book|last=Abdelhay A. Sallam and Om P. Malik|title=Electric Distribution Systems|year=May 2011|publisher=IEEE Computer Society Press|isbn=9780470276822|page=21}}</ref> A radial system is arranged like a tree where each customer has one source of supply. A network system has multiple sources of supply operating in parallel. The [[secondary network]] is commonly found in big cities and is the most reliable system. Spot networks are used for concentrated loads. Radial systems are commonly used in rural or suburban areas. Radial systems usually include emergency connections where the system can be reconfigured in case of problems, such as a fault or required replacement. This can be done by opening and closing switches. It may be acceptable to close a loop for a short time. Long feeders experience [[voltage drop]] ([[power factor]] distortion) requiring capacitors to be installed. Reconfiguration, by exchanging the functional links between the elements of the system, represents one of the most important measures which can improve the operational performance of a distribution system. The problem of optimization through the reconfiguration of a power distribution system, in terms of its definition, is a historical single objective problem with constraints. Since 1975, when Merlin and Back<ref>Merlin, A.; Back, H. Search for a Minimal-Loss Operating Spanning Tree Configuration in an Urban Power Distribution System. In Proceedings of the 1975 Fifth Power Systems Computer Conference (PSCC), Cambridge, UK, 1–5 September 1975; pp. 1–18.</ref> introduced the idea of distribution system reconfiguration for active power loss reduction, until nowadays, a lot of researchers have proposed diverse methods and algorithms to solve the reconfiguration problem as a single objective problem. Some authors have proposed Pareto optimality based approaches (including active power losses and reliability indices as objectives). For this purpose, different artificial intelligence based methods have been used: microgenetic,<ref>Mendoza, J.E.; Lopez, M.E.; Coello, C.A.; Lopez, E.A. Microgenetic multiobjective reconfiguration algorithm considering power losses and reliability indices for medium voltage distribution network. IET Gener. Transm. Distrib. 2009, 3, 825–840.</ref> branch exchange,<ref>Bernardon, D.P.; Garcia, V.J.; Ferreira, A.S.Q.; Canha, L.N. Multicriteria distribution network reconfiguration considering subtransmission analysis. IEEE Trans. Power Deliv. 2010, 25, 2684–2691.</ref> particle swarm optimization<ref>Amanulla, B.; Chakrabarti, S.; Singh, S.N. Reconfiguration of power distribution systems considering reliability and power loss. IEEE Trans. Power Deliv. 2012, 27, 918–926.</ref> and non-dominated sorting genetic algorithm.<ref>[http://www.mdpi.com/1996-1073/6/3/1439/pdf Tomoiagă, B.; Chindriş, M.; Sumper, A.; Sudria-Andreu, A.; Villafafila-Robles, R. Pareto Optimal Reconfiguration of Power Distribution Systems Using a Genetic Algorithm Based on NSGA-II. Energies 2013, 6, 1439-1455. ]</ref> ==See also== {{too many see alsos|date=March 2016}} {{Portal|Energy|Sustainable development}} {{colbegin||25em}} * [[C37.94]] - IEEE standard / rules to interconnect tele-protection and multiplexer devices of power utility companies * [[Cost of electricity by source]] * [[Electricity distribution companies by country|Distribution companies by country]] * [[Electric generator]] * [[Electric utility]] * [[Electricity generation]] * [[Electricity retailing]] * [[Fault indicator]] * [[Fuse cutout]] * [[Infrastructure]] * [[List of energy storage projects]] * [[Load profile]] * [[Losses in electrical systems]] * [[Network protector]] * [[Power distribution unit]] * [[Power quality]] * [[Transmission system operator]] {{colend}} ==References== <references/> ==External links== {{Wikiversity|Distribution of Electrical Power}} *[http://www.ieee.org/pes IEEE Power Engineering Society] *[http://grouper.ieee.org/groups/td/dist/ IEEE Power Engineering Society Distribution Subcommittee] *[http://www.oe.energy.gov U.S. Department of Energy Electric Distribution website] {{Electricity generation}} {{Authority control}} {{DEFAULTSORT:Electricity Distribution}} [[Category:Electric power distribution| ]] [[Category:Electrical engineering]] [[de:Stromnetz#Verbundnetz]] [[sv:Elektricitet#Överföring]]'