Mains electricity

Mains electricity

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Mains is the general-purpose alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 (AC) electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

 supply. In the US, electric power is referred to by several names including household power, household electricity, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power. In many parts of Canada
Canadian English
Canadian English is the variety of English spoken in Canada. English is the first language, or "mother tongue", of approximately 24 million Canadians , and more than 28 million are fluent in the language...

, it is called hydro, because much of the Canadian electrical generating capacity is hydroelectric.

Mains power systems


For a list of voltages, frequencies, and wall plugs by country, see Mains electricity by country

Worldwide, many different mains power systems are found for the operation of household and light commercial electrical appliances and lighting. The different systems are primarily characterized by their
  • Voltage
    Voltage
    Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

  • Frequency
    Utility frequency
    The utility frequency, line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end-user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...

  • Plugs and sockets
    Domestic AC power plugs and sockets
    AC power plugs and sockets are devices for removably connecting electrically operated devices to the power supply. Electrical plugs and sockets differ by country in rating, shape, size and type of connectors...

     (a.k.a. receptacles or outlets)

but also by their
  • Earthing system
    Earthing system
    In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the power supply, and regulations can vary considerably among...

     (grounding)
  • Protection against overcurrent
    Overcurrent
    In electricity supply, overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible causes for overcurrent include short circuits, excessive load,...

     damage (e.g., due to short circuit), electric shock
    Electric shock
    Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....

    , and fire hazards
  • Parameter tolerances


All these parameters vary among regions. The voltages are generally in the range 100–240 V
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

 (always expressed as root-mean-square voltage). The two commonly used frequencies are 50 Hz and 60 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

.

Some territories use standards different from those of the countries they belong to (such as Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...

 in China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

, similar voltage but different AC power plugs and sockets). Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage and frequency from the surrounding areas. Some city areas may use standards different from that of the surrounding countryside (e.g. in Libya
Libya
Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west....

). Regions in an effective state of anarchy
Anarchy
Anarchy , has more than one colloquial definition. In the United States, the term "anarchy" typically is meant to refer to a society which lacks publicly recognized government or violently enforced political authority...

 may have no central electrical authority, with electric power provided by incompatible private sources.

Many other combinations of voltage and utility frequency
Utility frequency
The utility frequency, line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end-user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...

, including direct current, were formerly used, with frequencies between 25 Hz and 133 Hz and voltages from 100 to 250 V. The modern standard combinations
IEC 60038
International Standard IEC 60038 defines a set of standard voltages for use in low voltage and high voltage AC electricity supply systems.-Low voltage:...

 of 230 V/50 Hz and 120 V/60 Hz did not apply in the first few decades of the 20th century and are still not universal.

Industrial plants with polyphase power systems will have different, higher voltages installed for large equipment (and different sockets and plugs), but the common voltages listed here would still be found for lighting and portable equipment.

Building wiring


In most countries, household power is single-phase electric power
Single-phase electric power
In electrical engineering, single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors...

, with two or three wired contacts at each outlet.
  • The live wire
    Live wire (electricity)
    The live wire in an AC electrical circuit refers to the wire which carries an oscillating voltage with respect to the earth...

    (also known as phase, hot or active contact), carries alternating current
    Alternating current
    In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

     between the power grid
    Grid (electricity)
    An electrical grid is a vast, interconnected network for delivering electricity from suppliers to consumers. It consists of three main components: 1) generating plants that produce electricity from combustible fuels or non-combustible fuels ; 2) transmission lines that carry electricity from power...

     and the household.
  • The neutral wire completes the electrical circuit by also carrying alternating current
    Alternating current
    In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

     between the power grid
    Grid (electricity)
    An electrical grid is a vast, interconnected network for delivering electricity from suppliers to consumers. It consists of three main components: 1) generating plants that produce electricity from combustible fuels or non-combustible fuels ; 2) transmission lines that carry electricity from power...

     and the household. The neutral is staked into the ground as often as possible, and therefore has the same electrical potential as the earth. This prevents the power circuits from rising beyond earth, such as when they are struck by lightning or become otherwise charged.
  • The earth wire
    Ground (electricity)
    In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....

    or ground connects cases of equipment to earth ground as a protection against faults (Electric Shock).

Various earthing system
Earthing system
In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the power supply, and regulations can vary considerably among...

s are used to ensure that the ground and neutral wires have the correct voltages, to prevent shocks when touching grounded objects.

In some installations, there may be two live conductors which carry alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

s in a three wire single-phase circuit.

Small portable electrical equipment is connected to the power supply through flexible cables terminated in a plug
Domestic AC power plugs and sockets
AC power plugs and sockets are devices for removably connecting electrically operated devices to the power supply. Electrical plugs and sockets differ by country in rating, shape, size and type of connectors...

, which is then inserted into a fixed receptacle (socket). Larger household electrical equipment and industrial equipment may be permanently wired to the fixed wiring of the building. For example, in North American homes a window-mounted self-contained air conditioner unit would be connected to a wall plug, whereas the central air conditioning for a whole home would be permanently wired. Larger plug and socket combinations
Industrial and multiphase power plugs and sockets
Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets...

 are used for industrial equipment carrying larger currents, higher voltages, or three phase electric power.

Circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...

s and fuse
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...

s are used to detect short circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....

s between the live and neutral wires, or the drawing of more current than the wires are rated to handle to prevent overheating and fire. These protective devices are usually mounted in a central panel in a building, but some wiring systems also provide an over current protection device at the socket or within the plug.

Residual-current device
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...

s, also known as ground-fault circuit interrupters and appliance leakage current interrupters, are used to detect ground faults - leakage of current to somewhere other than the neutral and live wires (like the ground wire or a person). When a ground fault is detected, the device quickly cuts off the circuit.

Voltage levels


All of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, Africa, Asia, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 and most of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 use a supply that is within 6% of 230 V
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

, whereas Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

, North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and some parts of northern South America use a voltage between 100 and 127 V. The 230 V standard has become the most widespread so standard 230 V equipment can be used in most parts of the world with the aid of an adapter
Adapter
An adapter or adaptor is a person that adapts or a device that converts attributes of one device or system to those of an otherwise incompatible device or system.Some adapters may only affect physical attributes:...

 or a change to the equipment's connection plug for the specific country.

Measuring voltage


A distinction should be made between the voltage at the point of supply (nominal system voltage) and the voltage rating of the equipment (utilization voltage). Typically the utilization voltage is 3% to 5% lower than the nominal system voltage; for example, a nominal 208 V supply system will be connected to motors with "200 V" on their nameplates. This allows for the voltage drop
Voltage drop
Voltage drop is the reduction in voltage in the passive elements of an electrical circuit. Voltage drops across conductors, contacts, connectors and source internal resistances are undesired as they reduce the supplied voltage while voltage drops across loads and other electrical and electronic...

 between equipment and supply. Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages.

Power distribution system voltage is nearly sinusoidal in nature. Voltages are expressed as root mean square
Root mean square
In mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids...

 (RMS) voltage.
Voltage tolerances are for steady-state operation. Momentary heavy loads, or switching operations in the power distribution network, may cause short-term deviations out of the tolerance band. In general, power supplies derived from large networks with many sources are more stable than those supplied to an isolated community with perhaps only a single generator.

Choice of voltage


The choice of utilization voltage is due more to historical reasons than optimization of the distribution system—once a voltage is in use and equipment using this voltage is widespread, changing voltage is a drastic and expensive measure. A 230 V distribution system will use less conductor material to deliver a given amount of power because the current, and consequently the resistive loss, is lower than for a 120 V system. While large heating appliances can use smaller conductors at 230 V for the same output rating, few household appliances use anything like the full capacity of the outlet to which they are connected. Minimum wire size for hand-held or portable equipment is usually restricted by the mechanical strength of the conductors. Electrical appliances are used extensively in homes in both 230 V and 120 V system countries. National electrical codes prescribe wiring methods
Electrical wiring
Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to...

 intended to minimize the risk of electric shock and fire.

Many areas using (nominally) 120 V make use of three-wire, single-phase
Split phase
A split-phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial applications. It is the AC equivalent of the original Edison 3-wire direct current system...

 240 V systems to supply large appliances. Three-phase
Three-phase
In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are radians offset in time...

 systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment. Where both single-phase and three-phase loads are served by an electrical system, the system may be labelled with both voltages such as 120/208 or 230/400 V, to show the line-to-neutral voltage and the line-to-line voltage. Large loads are connected for the higher voltage. Other three-phase voltages, up to 830 volts, are occasionally used for special-purpose systems such as oil well pumps.

Large industrial motors (say, more than 250 HP or 150 kW) may operate on medium voltage. On 60 Hz systems a standard for medium voltage equipment is 2300/4160 V whereas 3300 V is the common standard for 50 Hz systems.

Standardization


Following voltage harmonization, electricity supplies within the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 are now nominally 230 V ± 6% at 50 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

. For a transition period (1995–2008), countries that had previously used 220 V changed to a narrower asymmetric tolerance range of 230 V +6% −10% and those (like the UK) that had previously used 240 V changed to 230 V +10% −6%. No change in voltage is required by either system as both 220 V and 240 V fall within the lower 230 V tolerance bands (230 V ±6%). In practice, this allows countries to continue to supply the same voltage (220 or 240 V), at least until existing supply transformers are replaced. Equipment used in these countries is designed to accept any voltage within the specified range.

In the United States and Canada, national standards specify that the nominal voltage at the source should be 120 V and allow a range of 114 to 126 V (−5% to +5%). Historically 110, 115 and 117 volts have been used at different times and places in North America. Main power is sometimes spoken of as 110; however, 120 is the nominal voltage.

In 2000, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 converted to 230 V as the nominal standard with a tolerance of +10% −6%., this superseding the old 240 V standard, AS2926-1987. As in the UK, 240 V is within the allowable limits and "240 volt" is a synonym for mains in Australian
Australian English
Australian English is the name given to the group of dialects spoken in Australia that form a major variety of the English language....

 and British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

.

In Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, the electrical power supply to households is at 100 V. Eastern and northern parts of Honshū
Honshu
is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...

 (including Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...

) and Hokkaidō
Hokkaido
, formerly known as Ezo, Yezo, Yeso, or Yesso, is Japan's second largest island; it is also the largest and northernmost of Japan's 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaido from Honshu, although the two islands are connected by the underwater railway Seikan Tunnel...

 have a frequency of 50 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

, whereas western Honshū (including Nagoya, Osaka, and Hiroshima), Shikoku
Shikoku
is the smallest and least populous of the four main islands of Japan, located south of Honshū and east of the island of Kyūshū. Its ancient names include Iyo-no-futana-shima , Iyo-shima , and Futana-shima...

, Kyūshū
Kyushu
is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....

 and Okinawa operate at 60 Hz. The boundary between the two regions contains four back-to-back HVDC substations which convert the frequency; these are Shin Shinano
Shin Shinano
is the designation of a back-to-back high-voltage direct current facility in Japan and the location of the Shin Shinano Frequency Converter Station.Shin Shinano is located at -HVDC plant:...

, Sakuma Dam, Minami-Fukumitsu
Minami-Fukumitsu
Minami-Fukumitsu is the name given to an HVDC back-to-back station for the interconnection of the power grids of West and Eastern Japan. This facility went in service in March 1999. It operates with a voltage of 125 kV and can transfer a power up to 300 megawatts. The station is located in Nanto,...

, and the Higashi-Shimuzu Frequency Converter
Higashi-Shimuzu Frequency Converter
Higashi-Shimizu Frequency Converter is the third facility in Japan for interconnecting the power grid of Eastern Japan, which is operated with 50 hertz to that of Western Japan, which is operated with 60 hertz....

. To accommodate the difference, frequency-sensitive appliances marketed in Japan can often be switched between the two frequencies.

History of voltage and frequency



The system of three-phase
Three-phase
In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are radians offset in time...

 alternating current electrical generation, transmission, and distribution was developed in the 19th century by Nikola Tesla
Nikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...

, George Westinghouse
George Westinghouse
George Westinghouse, Jr was an American entrepreneur and engineer who invented the railway air brake and was a pioneer of the electrical industry. Westinghouse was one of Thomas Edison's main rivals in the early implementation of the American electricity system...

 and others. Thomas Edison
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...

 developed direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 (DC) systems at 110 V and this was claimed to be safer in the battles between proponents of AC and DC supply systems (the War of Currents
War of Currents
In the "War of Currents" era in the late 1880s, George Westinghouse and Thomas Edison became adversaries due to Edison's promotion of direct current for electric power distribution over alternating current advocated by several European companies and Westinghouse Electric based out of Pittsburgh,...

). Edison chose 110 volts to make high-resistance carbon filament lamps
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

 both practical and economically competitive with gas lighting
Gas lighting
Gas lighting is production of artificial light from combustion of a gaseous fuel, including hydrogen, methane, carbon monoxide, propane, butane, acetylene, ethylene, or natural gas. Before electricity became sufficiently widespread and economical to allow for general public use, gas was the most...

. While higher voltages would reduce the current required for a given quantity of lamps, the filaments would become increasingly fragile and short-lived. Edison selected 100 volts for the lamp as a compromise between distribution costs and lamp costs. Generation was maintained at 110 volts to allow for a voltage drop
Voltage drop
Voltage drop is the reduction in voltage in the passive elements of an electrical circuit. Voltage drops across conductors, contacts, connectors and source internal resistances are undesired as they reduce the supplied voltage while voltage drops across loads and other electrical and electronic...

 between generator and lamp.

In the 1880s only carbon-filament incandescent lamps were available, designed for a voltage of around 100 volts. Later metal filament lamps became feasible. In 1899, the Berliner Elektrizitäts-Werke (BEW), a Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...

 electrical utility, decided to greatly increase its distribution capacity by switching to 220 volt nominal distribution, taking advantage of the higher voltage capability of metal filament lamps. The company was able to offset the cost of converting the customer's equipment by the resulting saving in distribution conductors cost. This became the model for electrical distribution in Germany and the rest of Europe and the 220-volt system became common. North American practice remained with voltages near 110 volts for lamps.

In 1883 Edison patented a three wire
Split phase
A split-phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial applications. It is the AC equivalent of the original Edison 3-wire direct current system...

 distribution system to allow DC generation plants to serve a wider radius of customers. This saved on copper costs since lamps were connected in series on a 220 volt system, with a neutral conductor connected between to carry any unbalance between the two sub-circuits. This was later adapted to AC circuits. Most lighting and small appliances ran on 120 V, while big appliances could be connected to 240 V. This system saved copper and was backward-compatible with existing appliances. Also, the original plugs could be used with the revised system.
At the end of the 19th century, Westinghouse in the US decided on 60 Hz and AEG in Germany decided on 50 Hz, eventually leading to the world being mostly divided into two frequency camps. Most 60 Hz systems are nominally 120 volts and most 50 Hz nominally 230 volts.

Voltage regulation


To maintain the voltage at the customer's service within the acceptable range, electrical distribution utilities use regulating equipment at electrical substation
Electrical substation
A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions...

s or along the distribution line. At a substation, the step-down transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

 will have an automatic on-load tap changer, allowing the ratio between transmission voltage and distribution voltage to be adjusted in steps. For long (several kilometers) rural distribution circuits, automatic voltage regulators may be mounted on poles of the distribution line. These are autotransformer
Autotransformer
An autotransformer is an electrical transformer with only one winding. The auto prefix refers to the single coil acting on itself rather than any automatic mechanism. In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where...

s again with on-load tapchangers to adjust the ratio depending on the observed voltage changes.

At each customer's service, the step-down transformer has up to five taps to allow some range of adjustment, usually ±5% of the nominal voltage. Since these taps are not automatically controlled, they are only used to adjust the long-term average voltage at the service and do not regulate the voltage seen by the utility customer.

See also


  • Domestic AC power plugs and sockets
    Domestic AC power plugs and sockets
    AC power plugs and sockets are devices for removably connecting electrically operated devices to the power supply. Electrical plugs and sockets differ by country in rating, shape, size and type of connectors...

  • Electricity
    Electricity
    Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

  • Energy meter
  • Mains electricity by country
  • Potential difference
  • Power connector
    Power connector
    Power connector may refer to:* AC power plugs and sockets* Industrial power plug* DC connector* Blade connector, commonly found in cars for quick connection of wiring to electrical components* IEC 60309 , so-called "Commando" plug and socket...

  • Three-phase electric power
    Three-phase electric power
    Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...

  • Meter Point Administration Number
    Meter Point Administration Number
    A Meter Point Administration Number, also known as MPAN, Supply Number or S-Number, is a 21-digit reference used in Great Britain to uniquely identify electricity supply points such as individual domestic residences. The gas equivalent is the Meter Point Reference Number...


External links