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Encyclopedia > Electricity distribution
11kV/400V-230V transformer in an older suburb of Wellington, New Zealand
11kV/400V-230V transformer in an older suburb of Wellington, New Zealand
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Electricity distribution is the penultimate stage in the delivery (before retail) of electricity to end users. It is generally considered to include medium-voltage (less than 50 kV) power lines, electrical substations and pole-mounted transformers, low-voltage (less than 1000 V) distribution wiring and sometimes electricity meters. Image File history File links Gnome-globe. ... Image File history File links Download high-resolution version (1024x1536, 473 KB) This is a photograph of a pole mounted distribution transformer in a suburb near Wellington, New Zealand. ... Image File history File links Download high-resolution version (1024x1536, 473 KB) This is a photograph of a pole mounted distribution transformer in a suburb near Wellington, New Zealand. ... Image File history File links Portal. ... Electricity delivery is the process that goes from generation of electricity in the power central to the use by the consumer. ... Electricity retailing is the final process in the delivery of electricity from generation to the consumer. ... Lightning strikes during a night-time thunderstorm. ... A 115 kV to 41. ... For other uses, see transformers. ... Typical US domestic electricity meter An electric meter or energy meter is a device that measures the amount of electrical energy supplied to a residence or business. ...

Contents

Description

History

In the early days of electricity generation to about 1900, direct current DC generators were connected to loads at the same voltage. The generation, transmission and loads had to be of the same voltage because there was no way of changing DC voltage levels, other than inefficient motor-generator sets. Low DC voltages were used (on the order of 100 volts) since that was a practical voltage for incandescent lamps, which were then the primary electrical load. The low voltage also required less insulation to be safely distributed within buildings.


The losses in a cable are proportional to the square of the current, the length of the cable, and the resistivity of the material, and are inversely proportional to cross-sectional area. Early transmission networks were already using copper, which is one of the best economically feasible conductors for this application. To reduce the current and copper required for a given quantity of power transmitted would require a higher transmission voltage, but no convenient efficient method existed to change the voltage level of DC power circuits. To keep losses to an economically practical level the Edison DC system needed thick cables and local generators. Early DC generating plants needed to be within about 1.5 miles of the farthest customer to avoid the need for excessively large and expensive conductors.


Introduction of alternating current

The adoption of alternating current (AC) for electricity generation following the War of Currents dramatically changed the situation. Power transformers, installed at substations, could be used to raise the voltage from the generators and reduce it to supply loads. Increasing the voltage reduced the current in the transmission and distribution lines and hence the size of conductors required and distribution losses incurred. This made it more economical to distribute power over long distances. Generators (such as hydroelectric sites) could be located far from the loads. City lights viewed in a motion blurred exposure. ... Electricity generation is the first process in the delivery of electricity to consumers. ... In the War of Currents era in the late 1880s, George Westinghouse and Thomas Edison became adversaries due to Edisons promotion of direct current (DC) for electric power distribution over the alternating current (AC) advocated by Westinghouse and Nikola Tesla. ... For other uses, see transformers. ... A 115 kV to 41. ... Hydroelectric dam diagram The waters of Llyn Stwlan, the upper reservoir of the Ffestiniog Pumped-Storage Scheme in north Wales, can just be glimpsed on the right. ...


In North America, early distribution systems used a voltage of 2200 volts corner-grounded delta. Over time, this was gradually increased to 2400 volts. As cities grew, most 2400 volt systems were upgraded to 4160/2400 volt, three-phase systems. Some city and suburban distribution systems continue to use this range of voltages, but most have been converted to 7200/12470Y, 7620/13200Y, 14400/24940Y, and 19920/34500Y. In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are 2π/3 radians (120°,1/3 of a cycle) offset in time. ...


European systems used 3300 volts to ground, in support of the 220/380Y volt power systems used in those countries. In the UK, urban systems progressed to 6.6 kV and then 11 kV (phase to phase), the most common distribution voltage.


North American and European power distribution systems also 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 1-3 houses, whereas in the UK a typical urban or suburban low-voltage substation might be rated at 2 MW and supply a whole neighbourhood. This is because the higher voltage used in Europe (380 V vs 230 V) may be carried over a greater distance with acceptable power loss. An advantage of the North American setup is that failure or maintenance on a single transformer will only affect a few customers. Advantages of the UK setup are that the transformers may be fewer, larger and more efficient, and due to diversity there need be less spare capacity in the transformers, reducing power wastage. In North American city areas with many customers per unit area, network distribution will be used, with multiple transformers and low-voltage busses interconnected over several city blocks. The megawatt (symbol: MW) is a unit for measuring power corresponding to one million (106) watts. ...


Rural Electrification systems, in contrast to urban systems, tend to use higher voltages because of the longer distances covered by those distribution lines (see Rural Electrification Administration). 7200, 12470 and 25000 volt distribution is common in the United States; 11 kV and 33 kV are common in the UK, New Zealand and Australia; 11 kV and 22 kV are common in South Africa. Other voltages are occasionally used. Rural electrification is the process of bringing electrical power to rural and remote areas. ... The Rural Utilities Service, formerly the Rural Electrification Administration is charged with providing utilities (electricity, telephone, water, sewer, etc. ...


In New Zealand, Australia, Saskatchewan, Canada, and South Africa, single wire earth return systems (SWER) are used to electrify remote rural areas. Motto: Multis E Gentibus Vires (Latin: From many peoples strength) Official languages English Flower Western Red Lily Tree Paper Birch Bird Sharp-tailed Grouse Capital Regina Largest city Saskatoon Lieutenant-Governor Gordon Barnhart Premier Lorne Calvert (NDP) Parliamentary representation  - House seats  - Senate seats 14 6 Area Total  - Land  - Water  (% of... 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. ...


While power electronics now allow for conversion between DC voltage levels, AC is still used in distribution due to the economy, efficiency and reliabilty of transformers. High-voltage DC is used for transmission of large blocks of power over long distances, or for interconnecting adjacent AC networks, but not for distribution to customers. 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. ...


Distribution network configurations

Distribution networks are typically of two types, radial or interconnected (see Spot Network Substations). A radial network leaves the station and passes through the network area with no normal connection to any other supply. This is typical of long rural lines with isolated load areas. An interconnected network is generally found in more urban areas and will have multiple connections to other points of supply. Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ...


These points of connection are normally open but allow various configurations by the operating utility linemen carefully closing and opening switches. The benefit of the interconnected model is that in the event of a fault or required maintenance a small area of network can be isolated and the remainder kept on supply. There are various types of faults: In document ISO/CD 10303-226, a fault is defined as an abnormal condition or defect at the component, equipment, or sub-system level which may lead to a failure. ...


Within these networks there may be a mix of overhead line construction utilizing traditional utility poles and wires and, increasingly, underground construction with cables and indoor or cabinet substations. However, underground distribution can cost as much as 11 times as much as overhead construction. In part to reduce this cost, underground power lines are sometimes colocated with other utility lines in what are called Common utility ducts. Distribution feeders emanating from a substation are generally controlled by a circuit breaker or fuse which will open when a fault is detected. Automatic Circuit Reclosers may be installed to further segregate the feeder thus minimising the impact of faults. Pole carrying telephone, electricity and Cable TV equipment. ... A common utility duct, sometimes called a common utility conduit, is any structure - above, on, or below ground - that carries more than two types of public utility lines. ... A 2 pole MCB A circuit breaker is an automatically-operated electrical switch which is designed to protect an electrical circuit from damage caused by overload or short circuit. ... Look up fuse in Wiktionary, the free dictionary. ...


Long feeders experience voltage drop requiring capacitors or voltage regulators to be installed, and the phase physical relationship to be interchanged. This article or section does not cite its references or sources. ...


Characteristics of the supply given to customers are generally mandated by contract between the supplier and customer. Deviations from the normal usage pattern usually invoke monthly surcharges. Variables include: A contract is a legally binding exchange of promises or agreement between parties. ...

  • AC or DC - Virtually all public electricity supplies are AC today. Users of large amounts of DC power such as some electric railways, telephone exchanges and industrial processes such as aluminium smelting either operate their own or have adjacent dedicated generating equipment, or use rectifiers to derive DC from the public AC supply
  • Voltage, including tolerance (usually +10 or -15 percentage)
  • Frequency, commonly 50 & 60 Hz, 16-2/3 Hz for some railways and, in a few older industrial and mining locations, 25 Hz
  • Phase configuration (single phase, polyphase including two phase and three phase)
  • Maximum demand (usually measured as the largest amount of power delivered within a 15 or 30 minute period during a billing period)
  • Load Factor, expressed as a ratio of average load to peak load over a period of time. Load factor indicates the degree of effective utilization of equipment (and capital investment) of distribution line or system.
  • Power factor of connected load
  • Earthing arrangements - TT, TN-S, TN-C-S or TN-C
  • Maximum prospective short circuit current
  • Maximum level and frequency of occurrence of transients

See List of countries with mains power plugs, voltages and frequencies. City lights viewed in a motion blurred exposure. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Overhead wire in Coventry, England Overhead wire and its suspension system in Bridgeport, Connecticut, USA A railway electrification system is a way of supplying electric power to electric locomotives and multiple units. ... A Verizon Central Office in Lakeland, Florida at night. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... The percent sign A percentage is a way of expressing numbers as fractions of 100 and is often denoted using the percent sign, %. For example, 45. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... The hertz (symbol: Hz) is the SI unit of frequency. ... The generation of AC electric power is commonly three phase, in which the waveforms of three supply conductors are offset from one another by 120°. These three conductors are commonly housed in a single conduit (e. ... A polyphase system is a means of distributing alternating current electrical power. ... Two-phase electrical power was used in some early 20th century factories and the distribution systems that served them. ... In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are 2Ï€/3 radians (120°,1/3 of a cycle) offset in time. ... The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power. ... In electricity supply a TT earthing system is one where there is no metallic connection at all between the customers earth and the neutral terminal of the transformer in the suppliers network. ... A TN-S earthing system is one where where earth and neutral run separately right back to the supply. ... A TN-C-S earthing system is one where where earth and neutral are combined in the supply wiring but are separate in the installation. ... A TN-C earthing system is one where where earth and neutral are combined in the supply wiring and right through the install. ... The maximum prospective short circuit current is the maximum electrical current which can flow in a particular electrical system under short circuit conditions. ... Transient means passing with time. ... Line voltage is often also called mains voltage, power supply voltage, supply voltage, or system voltage. ...


Modern Distribution Systems

The modern distribution system begins as the primary circuit leaves the sub-station and ends as the secondary service enters the lines. An example of this type of fault would be a primary phase falling across the secondary lines. Another example would be some type of fault in the transformer itself.

Electric distribution substations transform power from transmission voltage to the lower voltage used for local distribution to homes and businesses.
Electric distribution substations transform power from transmission voltage to the lower voltage used for local distribution to homes and businesses.

The other type of primary configuration is known as delta, this method is older and less common. Delta is so named because of the shape of the Greek letter delta, a triangle. Delta consists of only 3 phases and no neutral. In delta there is only a single voltage, between two phases (phase to phase), while in wye there are two voltages, between two phases and between a phase and neutral (phase to neutral). Wye primary is safer because if one phase becomes grounded, that is makes connection to the ground through a person, tree, or other object, it should trip out the fused cutout similer to a household circuit breaker tripping. In delta, if a phase makes connection to ground it will continue to function normally. It takes two or three phases to make connection to ground before the fused cutouts will open the circuit. Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (1280 × 960 pixel, file size: 234 KB, MIME type: image/jpeg) Night photo of a common electric substation. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (1280 × 960 pixel, file size: 234 KB, MIME type: image/jpeg) Night photo of a common electric substation. ...


Economic and Political

In the United States, Electric industry "deregulation" reform, started in the mid-1990s, has led to the creation of electricity markets through the elimination of the former natural monopoly of generation, transmission, and distribution. As a consequence, electricity has become more of a commodity. The separation has also led to the development of new terminology to describe the business units, e.g. line company, wires business and network company. An electricity market is a system for effecting the purchase and sale of electricity using supply and demand to set the price. ... In economics, the term natural monopoly is used to refer to two different things. ...


See also

A common utility duct, sometimes called a common utility conduit, is any structure - above, on, or below ground - that carries more than two types of public utility lines. ... Electrical utility is a company that engages in the generation, transmission, and distribution of electricity for sale generally in a in regulated markets. ... Distributed generation is a new trend in the generation of heat and electrical power. ... A virtual power plant is a cluster of distributed generation installations (such as microCHP, wind-turbines, hydrogen stations, back-up gensets etc. ... Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. ... Electricity generation is the first process in the delivery of electricity to consumers. ... Transmission towers Transmission lines in Lund, Sweden Electric power transmission, or more accurately Electrical energy transmission, is the second process in the delivery of electricity to consumers. ... Electricity retailing is the final process in the delivery of electricity from generation to the consumer. ... Future energy development faces great challenges due to an increasing world population, demands for higher standards of living, demands for less pollution and a much-discussed end to fossil fuels. ... Linemen repairing overhead lines (that supply power to trains) Linemen repairing electricity distribution lines (that supply power to homes) A lineman or linesman is a tradesman who constructs and maintains electric power transmission and distribution facilities. ... In electronics, a load profile is a graph of the changes in the electrical load on an electrical device versus time. ... A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. ... Power quality is a term used to discuss events on electric power grids that can damage or disrupt sensisitive electronic devices. ... This article or section does not cite its references or sources. ...

References

External links

Further reading

  • Brown, R. E., Electric Power Distribution Reliability, Marcel Dekker, Inc., 2002.
  • Burke, J., Power Distribution Engineering, Marcel Dekker, Inc., 1994.
  • Hoffman, P., Scheer, R., Marchionini, B., Distributed Energy Resources: A Key Element of Grid Modernization DE - March/April 2004 [2]
  • Short, T. A. Electric Power Distribution Handbook, CRC Press, 2004.
  • Westinghouse Electric Corporation, Distribution Systems, vol. 3, 1965.
  • Westinghouse Electric Corporation, Electric power transmission patents; Tesla polyphase system. (Transmission of power; polyphase system; Tesla patents)
  • Willis, H. L., Power Distribution Planning Reference Book, Marcel Dekker, Inc., 2nd ed., 2004.
Sustainability and Development of Energy   Edit
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  Results from FactBites:
 
Electricity Distribution (474 words)
For electric customers like hospitals, banks and government facilities, continuous electric power is essential to daily operations and these temporary failures can have serious impacts.
These electric customers often benefit from backup power, or small generating facilities installed at or inside their buildings that can provide electricity when the grid is not working.
In addition to determining where new distribution lines should be built, the utilities also consider more immediate options for combating congestion by encouraging customers to pursue energy efficiency and asking key customers with high demand to cut back their loads on days when the area's demand is at its peak.
Electricity distribution - Wikipedia, the free encyclopedia (1083 words)
Electricity distribution is the final stage in the delivery of electricity.
In the early days of electricity generation, direct current (DC) generators were connected to loads at the same voltage.
Electricity industry reform has led to the creation of electricity markets through the separation of contestable retailing from distribution, a natural monopoly and the separation of the monopoly transmission from generation.
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