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50-619: In 1937, two committees of citizens from three counties sought aid to construct a local rural electric distribution system under the New Deal 's Rural Electrification Administration . They formed the Southern Maryland Tri-County Electric Cooperative Association, which was reorganized as a cooperative under the SMECO name in 1942. Customers were allowed to select suppliers of electricity beginning in 2001 under

100-599: A three phase supply may be made available for larger properties. Seen with an oscilloscope , the domestic power supply in North America would look like a sine wave , oscillating between −170 volts and 170 volts, giving an effective voltage of 120 volts RMS. Three-phase electric 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 connection

150-412: A utility pole , to a customer's building or other premises. It is the point where electric utilities provide power to their customers. The customer connection to an underground distribution system is usually called a "service lateral". Conductors of a service drop or lateral are usually owned and maintained by the utility company, but some industrial drops are installed and owned by the customer. At

200-456: A "main" fuse or circuit breaker , which controls all of the electric current entering the building at once, and a number of smaller fuses/breakers, which protect individual branch circuits. There is always provision for all power to be cut off by operating either a single switch or small number of switches (maximum of six in the United States, for example); when circuit breakers are used this

250-585: A complaint with the US Federal Energy Regulatory Commission (FERC), alleging that the Maryland Public Service Commission (PSC) coerced utilities into purchasing excess solar power generated by the state's community solar program at much higher retail rates, rather than paying the amount it would have cost these utilities to generate the power themselves, also known as the avoided cost. This would be in violation of

300-459: A generating station, where the potential difference can be as high as 33,000 volts. AC is usually used. Users of large amounts of DC power such as some railway electrification systems , telephone exchanges and industrial processes such as aluminium smelting use rectifiers to derive DC from the public AC supply, or may have their own generation systems. High-voltage DC can be advantageous for isolating alternating-current systems or controlling

350-545: 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, branch exchange, particle swarm optimization and non-dominated sorting genetic algorithm . Rural electrification systems tend to use higher distribution voltages because of

400-417: A mile away because they used a low voltage (110 V) from generation to end use. The low voltage translated to higher current and required thick copper cables for transmission. In practice, Edison's DC generating plants needed to be within about 1.5 miles (2.4 km) of the farthest customer to avoid even thicker and more expensive conductors. The problem of transmitting electricity over longer distances became

450-492: A neutral conductor. Rural distribution system may have long runs of one phase conductor and a neutral. In other countries or in extreme rural areas the neutral wire is connected to the ground to use that as a return (single-wire earth return). Electricity is delivered at a frequency of either 50 or 60 Hz, depending on the region. It is delivered to domestic customers as single-phase electric power . In some countries as in Europe

500-558: A recognized engineering roadblock to electric power distribution, with many less-than-satisfactory solutions tested by lighting companies. But the mid-1880s saw a breakthrough with the development of functional transformers that allowed AC power to be "stepped up" to a much higher voltage for transmission, then dropped down to a lower voltage near the end user. Compared to direct current, AC had much cheaper transmission costs and greater economies of scale — with large AC generating plants capable of supplying whole cities and regions, which led to

550-430: A single generating station to supply a string of lights up to 7 miles (11 km) long. And each doubling of voltage would allow a given cable to transmit the same amount of power four times the distance than at the lower voltage (with the same power loss). By contrast, direct-current indoor incandescent lighting systems, such as Edison's first power station , installed in 1882, had difficulty supplying customers more than

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600-742: A third of the east's capacity, and power in the west could not be fully shared with the east since the country does not have a common frequency. There are four high-voltage direct current (HVDC) converter stations that move power across Japan's AC frequency border. Shin Shinano is a 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 , Minami-Fukumitsu and Sakuma Dam . Together they can move up to 1.2 GW of power east or west. Most modern North American homes are wired to receive 240 volts from

650-475: Is also available, or may be generated locally. Large industrial customers have their own transformer(s) with an input from 11 kV to 220 kV. Most of the Americas use 60 Hz AC, the 120/240 volt split-phase system domestically and three phase for larger installations. North American transformers usually power homes at 240 volts, similar to Europe's 230 volts. It is the split-phase that allows use of 120 volts in

700-420: Is combined with electricity produced elsewhere. For alternating-current generators, all generating units connected to a common network must be synchronized , operating at the same frequency within a small tolerance. Alternatively, disparate sources can be combined to serve a common load if some external power converter, such as a rotating machine or a direct current converter system is interposed. Electricity

750-506: Is common in Canada, and 380-415 V or 690 V three-phase is found in European and many other countries. Generally, higher voltages are used for heavy industrial loads, and lower voltages for commercial applications. In North America where single-phase distribution transformers for service drops are the norm, three-phase service drops are often constructed using three single-phase transformers, wired in

800-400: Is consumed as soon as it is produced. It is transmitted at a very high speed, close to the speed of light . Primary distribution voltages range from 4 kV to 35 kV phase-to-phase (2.4 kV to 20 kV phase-to-neutral) Only large consumers are fed directly from distribution voltages; most utility customers are connected to a transformer, which reduces the distribution voltage to

850-404: Is economical with the higher density of housing in Europe. The service drop consists of three phase wires and a neutral wire which is grounded. Each phase wire provides around 230 V to loads connected between it and the neutral. Each of the phase wires carries 50 Hz alternating current which is 120° out of phase with the other two. Several slightly different voltage standards have been used in

900-415: Is made up of a neutral line connected to the transformer's center tap and two lines connected to the ends of the winding which provide 120V with respect to the neutral line. When these lines are insulated and twisted together, they are referred to as a triplex cable which may contain a supporting messenger cable in the middle of the neutral conductor to provide strength for long spans. The neutral line from

950-430: 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 systems can be TT, TN-S, TN-C-S or TN-C. Most of

1000-411: Is provided by the main circuit breaker. In North America, the 120/240 V split phase system is used for residential service drops. A pole-mounted single phase distribution transformer usually provides power for one or two residences. The secondary winding of the transformer provides 240 volts between its ends and is center tapped. The service drop, to a weatherhead on the premises being supplied,

1050-571: The Maryland Electric Deregulation legislation enacted in 1999. From 2007 to 2011, SMECO won the J.D. Power and Associates award for best customer service for a midsize utility. SMECO owned a 77 MW gas turbine generator located at the Chalk Point Generating Station , which began operation in 1990 and was operated and maintained by NRG Energy . In 2015, NRG acquired the turbine plant from SMECO. SMECO has filed

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1100-460: The federal Public Utility Regulatory Policies Act (PURPA), which establishes that any payment given to such qualifying power plants should equate to the utility's avoided cost. In addition, PURPA mandates that these plants do not exceed 80 MW of power. Recently, the development of community solar programs has become increasingly prevalent to meet the ever-growing demand for new, viable energy sources. However, there has been much controversy regarding

1150-670: The 1880s, when electricity started being generated at power stations . Until then, electricity was usually generated where it was used. The first power-distribution systems installed in European and US cities were used to supply lighting: arc lighting running on very-high-voltage (around 3,000 V) alternating current (AC) or direct current (DC), and incandescent lighting running on low-voltage (100 V) direct current. Both were supplanting gas lighting systems, with arc lighting taking over large-area and street lighting, and incandescent lighting replacing gas lights for business and residential users. The high voltages used in arc lighting allowed

1200-491: The 20th century, in many places the electric power industry was vertically integrated , meaning that one company did generation, transmission, distribution, metering and billing. Starting in the 1970s and 1980s, nations began the process of deregulation and privatization , leading to electricity markets . The distribution system would remain regulated, but generation, retail, and sometimes transmission systems were transformed into competitive markets. Electric power begins at

1250-469: The UK a typical urban or suburban low-voltage substation would normally be rated between 150 kVA and 1 MVA and supply a whole neighbourhood of a few hundred houses. Transformers are typically sized on an average load of 1 to 2 kW per household, and the service fuses and cable is sized to allow any one property to draw a peak load of perhaps ten times this. For industrial customers, 3-phase 690 / 400 volt

1300-412: The building for a three phase service. Single-phase distribution, with one live wire and the neutral is used domestically where total loads are light. In Europe, electricity is normally distributed for industry and domestic use by the three-phase, four wire system. This gives a phase-to-phase voltage of 400 volts wye service and a single-phase voltage of 230 volts between any one phase and neutral. In

1350-527: The current energy market. Electricity distribution Electric power distribution is the final stage in the delivery of electricity . Electricity is carried from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2  kV and 33 kV with the use of transformers . Primary distribution lines carry this medium voltage power to distribution transformers located near

1400-442: The customer's premises, the wires usually enter the building through a weatherhead that protects against entry of rain and snow, and drop down through conduit to an electric meter which measures and records the power used for billing purposes, then enters the main service panel . The utility's portion of the system ends, and the customer's wiring begins, at the output socket of the electric meter. The service panel will contain

1450-457: The customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment and household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops . Customers demanding a much larger amount of power may be connected directly to

1500-432: The electricity from the transmission networks would be shared among the customers. Today's distribution systems are heavily integrated with renewable energy generations at the distribution level of the power systems by the means of distributed generation resources, such as solar energy and wind energy . As a result, distribution systems are becoming more independent from the transmission networks day-by-day. Balancing

1550-545: The entire country was wired. Today the frequency is 50 Hz in Eastern Japan (including Tokyo, Yokohama , Tohoku , and Hokkaido ) and 60 Hz in Western Japan (including Nagoya , Osaka , Kyoto , Hiroshima , Shikoku , and Kyushu ). 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

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1600-588: The home. In the electricity sector in Japan , the standard voltage is 100 V, with both 50 and 60 Hz AC frequencies being used. Parts of the country use 50 Hz, while other parts use 60 Hz. This is a relic from the 1890s. 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

1650-530: The longer distances covered by distribution lines (see Rural Electrification Administration ). 7.2, 12.47, 25, and 34.5 kV distribution is common in the United States; 11 kV and 33 kV are common in the UK, Australia and New Zealand; 11 kV and 22 kV are common in South Africa; 10, 20 and 35 kV are common in China. Other voltages are occasionally used. Rural services normally try to minimize

1700-518: The low voltage "utilization voltage", "supply voltage" or "mains voltage" used by lighting and interior wiring systems. Distribution networks are divided into two types, radial or network. 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. Spot networks are used for concentrated loads. Radial systems are commonly used in rural or suburban areas. Radial systems usually include emergency connections where

1750-417: 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 introduced the idea of distribution system reconfiguration for active power loss reduction, until nowadays,

1800-694: The number of poles and wires. 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. In New Zealand , Australia , Saskatchewan, Canada , and South Africa , Single-wire earth return systems (SWER) are used to electrify remote rural areas. Three phase service provides power for large agricultural facilities, petroleum pumping facilities, water plants, or other customers that have large loads (three-phase equipment). In North America, overhead distribution systems may be three phase, four wire, with

1850-405: The past as well: 220Y380, 230Y400 and 240Y415, with plans for future "harmonization" towards 230Y400. In this notation, the first number is the voltage between a phase wire and neutral, and the second number, after the "Y", is the line voltage (between any two-phase wires). Other countries, such as the UK and Ireland, generally provide a single phase and neutral per house, with every third house on

1900-833: The pole is connected to a ground near the service panel; often a conductive rod driven into the earth. The service drop provides the building with two 120 V lines of opposite phase , so 240 V can be obtained by connecting a load between the two 120 V conductors, while 120 V loads are connected between either of the two 120 V lines and the neutral line. 240 V circuits are used for high-demand devices, such as air conditioners , water heaters , clothes dryers , ovens and boilers , while 120 V circuits are used for lighter loads such as lighting and ordinary small appliance outlets. In many European countries and other countries that use European systems, three-phase service drops are often used for domestic residences. The use of three-phase power allows longer service drops to serve multiple residences, which

1950-422: The primary distribution level or the subtransmission level. The transition from transmission to distribution happens in a power substation , which has the following functions: Urban distribution is mainly underground, sometimes in common utility ducts . Rural distribution is mostly above ground with utility poles , and suburban distribution is a mix. Closer to the customer, a distribution transformer steps

2000-447: The primary distribution power down to a low-voltage secondary circuit, usually 120/240 V in the US for residential customers. The power comes to the customer via a service drop and an electricity meter . The final circuit in an urban system may be less than 15 metres (50 ft) but may be over 91 metres (300 ft) for a rural customer. Electric power distribution become necessary only in

2050-459: The quantity of electricity transmitted. For example, Hydro-Québec has a direct-current line which goes from the James Bay region to Boston . From the generating station it goes to the generating station's switchyard where a step-up transformer increases the voltage to a level suitable for transmission, from 44 kV to 765 kV. Once in the transmission system, electricity from each generating station

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2100-544: The same phase. In Australian service drops, to avoid having unprotected cables within the building up to the service panel main switch, a fuse for each phase is provided at the point-of-attachment, at the weatherhead - called a "raiser bracket" in Australia - or on the outside of the building. One or more removable ceramic "fuse holders", containing an appropriately sized service fuse for each phase protects all cables beyond this point. These fuses may be removed and replaced by

2150-412: The supply authority in the event of a fault causing them to "operate". This box is termed a "Fused Overhead Line Connector Box" (FOLCB). Commercial and industrial service drops can be much bigger, and are usually three phase . In the US, common services are 120Y/208 (three 120 V circuits 120 degrees out of phase, with 208 V line-to-line), 240 V three-phase, and 480 V three-phase. 600 V three-phase

2200-431: The supply-demand relationship at these modern distribution networks (sometimes referred to as microgrids ) is extremely challenging, and it requires the use of various technological and operational means to operate. Such tools include battery storage power station , data analytics , optimization tools, etc. Service drop In electric power distribution , a service drop is an overhead electrical line running from

2250-469: The surge in net metering consumers due to the resulting cost shifts, which negatively affect the non-solar community now facing much higher payments to offset the increased benefits given to solar projects. Because of the continual reduction in the cost of power, FERC has become more concerned with the discrepancy between avoided costs and prevailing wholesale prices. This has placed more focus on PURPA's roles and responsibilities in maintaining and balancing

2300-425: The system can be reconfigured in case of problems, such as a fault or planned maintenance. This can be done by opening and closing switches to isolate a certain section from the grid. Long feeders experience voltage drop ( power factor distortion) requiring capacitors or voltage regulators to be installed. Reconfiguration, by exchanging the functional links between the elements of the system, represents one of

2350-472: The transformer, and through the use of split-phase electrical power , can have both 120 volt receptacles and 240 volt receptacles. The 120 volts is typically used for lighting and most wall outlets . The 240 volt circuits are typically used for appliances requiring high watt heat output such as ovens and heaters. They may also be used to supply an electric car charger. Traditionally, the distribution systems would only operate as simple distribution lines where

2400-404: The use of AC spreading 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, highlighting the deaths caused by high-voltage AC systems over the years and claiming any AC system

2450-423: The world uses 50 Hz 220 or 230 V single phase, or 400 V three-phase for residential and light industrial services. In this system, the primary distribution network supplies a few substations per area, and the 230 V / 400 V power from each substation is directly distributed to end users over a region of normally less than 1 km radius. Three live (hot) wires and the neutral are connected to

2500-448: Was inherently dangerous. 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. In the first half of

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