![Access to Electricity](https://upload.wikimedia.org/wikipedia/commons/7/75/Access_to_Electricity.svg)
Mains electricity or utility power, power grid, domestic power, and wall power, or in some parts of Canada as hydro, is a general-purpose
alternating-current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...
(AC)
electric power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions ...
supply. It is the form of electrical power that is delivered to homes and businesses through the
electric grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
in many parts of the world. People use this electricity to power everyday items—such as domestic appliances, televisions and lamps—by plugging them into a wall outlet.
The
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
and
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of electric power differs between regions. In much of the world, a voltage (nominally) of 230 volts and frequency of 50 Hz is used. In North America, the most common combination is 120 V and a frequency of 60 Hz. Other combinations exist, for example, 230 V at 60 Hz. Travellers' portable appliances may be inoperative or damaged by foreign electrical supplies. Non-interchangeable
plugs and sockets in different regions provide some protection from accidental use of appliances with incompatible voltage and frequency requirements.
Terminology
![Mains powered electric Lamp](https://upload.wikimedia.org/wikipedia/commons/0/06/Mains_powered_electric_Lamp.JPG)
In the US, mains electric power is referred to by several names including "utility power", "household power", "household electricity", "house current", "powerline", "domestic power", "wall power", "line power", "AC power", "city power", "street power", and "120 (one twenty)".
In the UK, mains electric power is generally referred to as "the mains". More than half of power in Canada is
hydroelectricity
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...
, and mains electricity is often referred to as "hydro" in some regions of the country. This is also reflected in names of current and historical electricity utilities such as
Hydro-Québec
Hydro-Québec is a public utility that manages the generation, transmission and distribution of electricity in the Canadian province of Quebec, as well as the export of power to portions of the Northeast United States.
It was established by t ...
,
BC Hydro
The British Columbia Hydro and Power Authority, operating as BC Hydro, is a Canadian electric utility in the province of British Columbia. It is the main electricity distributor, serving more than 4 million customers in most areas, with the exce ...
,
Manitoba Hydro
The Manitoba Hydro-Electric Board, operating as Manitoba Hydro, is the electric power and natural gas utility in the province of Manitoba, Canada. Founded in 1961, it is a provincial Crown Corporation, governed by the Manitoba Hydro-Electric Boa ...
, and
Hydro One (one of the entities resulting from the breakup of
Ontario Hydro
Ontario Hydro, established in 1906 as the Hydro-Electric Power Commission of Ontario, was a publicly owned electricity utility in the Province of Ontario. It was formed to build transmission lines to supply municipal utilities with electricity g ...
). Although these is an entity named
Newfoundland and Labrador Hydro, that company is primarily a hydroelectricity generator, though it also directly serves customers in Labrador and some other parts of
the province
''The Province'' is a daily newspaper published in tabloid format in British Columbia by Pacific Newspaper Group, a division of Postmedia Network, alongside the '' Vancouver Sun'' broadsheet newspaper. Together, they are British Columbia's ...
. The majority of customers on the
island of Newfoundland
Newfoundland (, ; french: link=no, Terre-Neuve, ; ) is a large island off the east coast of the North American mainland and the most populous part of the Canadian province of Newfoundland and Labrador. It has 29 percent of the province's land ...
deal with
Newfoundland Power
Newfoundland Power Inc. is an electric utility owned by Fortis Inc. which is the primary retailer of electric power in the Canadian province of Newfoundland and Labrador. The company was formed by the Royal Securities Corporation of Montreal in 1 ...
as their service provider, and thus electricity is more commonly called simply "power" in that province.
Power systems
Worldwide, many different
mains power systems
Mains electricity by country includes a list of countries and territories, with the plugs, voltages and frequencies they commonly use for providing electrical power to low voltage appliances, equipment, and lighting typically found in homes an ...
are found for the operation of household and light commercial electrical appliances and lighting. The different systems are primarily characterized by their
*
Voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
*
Frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
*
Plugs and sockets (receptacles or outlets)
*
Earthing system
An earthing system (UK and IEC) or grounding system (US) connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes. The choice of earthing system can affect ...
(grounding)
* Protection against
overcurrent
In an electric power system, 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 caus ...
damage (e.g., due to short circuit),
electric shock
Electrical injury is a physiological reaction caused by electric current passing through the body. The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or produce a ...
, and fire hazards
* Parameter tolerances.
All these parameters vary among regions. The voltages are generally in the range 100–240
V (always expressed as
root-mean-square
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the ...
voltage). The two commonly used frequencies are 50
Hz and 60 Hz.
Single-phase
In electrical engineering, single-phase electric power (abbreviated 1φ) is 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 loa ...
or
three-phase
Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional neutral ...
power is most commonly used today, although two-phase systems were used early in the 20th century. Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage or frequency from the surrounding areas. Some city areas may use standards different from that of the surrounding countryside (e.g. in
Libya
Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to the east, Suda ...
). Regions in an effective state of
anarchy
Anarchy is a society without a government. It may also refer to a society or group of people that entirely rejects a set hierarchy. ''Anarchy'' was first used in English in 1539, meaning "an absence of government". Pierre-Joseph Proudhon adopte ...
may have no central electrical authority, with electric power provided by incompatible private sources.
Many other combinations of voltage and
utility frequency
The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to ...
were formerly used, with frequencies between 25 Hz and 133 Hz and voltages from 100 V to 250 V.
Direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or ev ...
(DC) has been displaced by
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC) in public power systems, but DC was used especially in some city areas to the end of the 20th century. The modern combinations of 230 V/50 Hz and 120 V/60 Hz, listed in
IEC 60038
International Standard IEC 60038, ''IEC standard voltages'', defines a set of standard voltages for use in low voltage and high voltage AC and DC electricity supply systems.
Low voltage
Where two voltages are given below separated by "/", t ...
, did not apply in the first few decades of the 20th century and are still not universal. Industrial plants with
three-phase power 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.
Common uses of electricity
Electricity is used for lighting, heating, cooling, electric motors and electronic equipment. The
US Energy Information Administration
The U.S. Energy Information Administration (EIA) is a principal agency of the U.S. Federal Statistical System responsible for collecting, analyzing, and disseminating energy information to promote sound policymaking, efficient markets, and publ ...
(EIA) has published:
U.S. residential sector electricity consumption by major end uses in 2021
:
1 Includes televisions, set-top boxes, home theatre systems, DVD players, and video game consoles.
:
2 Includes desktop and laptop computers, monitors, and networking equipment.
:
3 Does not include water heating.
:
4 Includes small electric devices, heating elements, exterior lights, outdoor grills, pool and spa heaters, backup electricity generators, and motors not listed above. Does not include electric vehicle charging.
Electronic appliances such as computers or televisions sets typically use an AC to DC converter or
AC adapter
An AC adapter or AC/DC adapter is a type of external power supply, often enclosed in a case similar to an AC plug. Other common names include wall wart, power brick, wall charger, and power adapter. Adapters for battery-powered equipment may ...
to power the device. This is often capable of operation with a wide range of voltage and with both common power frequencies. Other AC applications usually have much more restricted input ranges.
Building wiring
Portable appliances use
single-phase electric power
In electrical engineering, single-phase electric power (abbreviated 1φ) is 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 ...
, with two or three wired contacts at each outlet. Two wires (neutral and live/active/hot) carry current to operate the device. A third wire, not always present, connects conductive parts of the appliance case to earth ground. This protects users from
electric shock
Electrical injury is a physiological reaction caused by electric current passing through the body. The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or produce a ...
if live internal parts accidentally contact the case.
In northern and central Europe, residential electrical supply is commonly 400 V three-phase electric power, which gives 230 V between any single phase and neutral; house wiring may be a mix of three-phase and single-phase circuits, but three-phase residential use is rare in the UK. High-power appliances such as
kitchen stove
A kitchen stove, often called simply a stove or a cooker, is a kitchen appliance designed for the purpose of cooking food. Kitchen stoves rely on the application of direct heat for the cooking process and may also contain an oven, used for ba ...
s, water heaters and household power heavy tools like
log splitter
A log splitter is a piece of machinery or equipment used for splitting firewood from softwood or hardwood logs that have been pre-cut into sections (rounds), usually by chainsaw or on a saw bench. Many log splitters consist of a hydraulic pump or ...
s may be supplied from the 400 V three-phase power supply.
Small portable electrical equipment is connected to the power supply through flexible cables terminated in a
plug, which is 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
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
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 are used for industrial equipment carrying larger currents, higher voltages, or three phase electric power.
Circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the ris ...
s and
fuses are used to detect
short circuit
A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circu ...
s between the line and neutral or ground wires or the drawing of more current than the wires are rated to handle (overload protection) to prevent overheating and possible fire. These protective devices are usually mounted in a central panel—most commonly a distribution board or consumer unit—in a building, but some wiring systems also provide a protection device at the socket or within the plug.
Residual-current device
A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) is an electrical safety device that quickly breaks an electrical circuit with leakage current to ground. It is to protect equi ...
s, also known as ground-fault circuit interrupters and appliance leakage current interrupters, are used to detect ''ground faults''—flow of current in other than the neutral and line wires (like the ground wire or a person). When a ground fault is detected, the device quickly cuts off the circuit.
Voltage levels
![World Map of Mains Voltages and Frequencies, Detailed](https://upload.wikimedia.org/wikipedia/commons/7/70/World_Map_of_Mains_Voltages_and_Frequencies%2C_Detailed.svg)
Most of the world population (
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
,
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
,
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
,
Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
,
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
, and much of
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
) use a supply that is within 6% of 230 V. In the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
and Australia the nominal supply voltage is 230 V +10%/−6% to accommodate the fact that most transformers are in fact still set to 240 V. The 230 V standard has become widespread so that 230 V equipment can be used in most parts of the world with the aid of an
adapter
An adapter or adaptor is a device that converts attributes of one electrical device or system to those of an otherwise incompatible device or system. Some modify power or signal attributes, while others merely adapt the physical form of one c ...
or a change to the equipment's plug to the standard for the specific country.
The
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
and
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
use a supply voltage of 120 volts ± 6%.
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
,
Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
,
Saudi Arabia
Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in Western Asia. It covers the bulk of the Arabian Peninsula, and has a land area of about , making it the fifth-largest country in Asia, the second-largest in the Ara ...
,
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
,
Central America
Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
and some parts of northern South America use a voltage between 100 V and 127 V. However, most of the households in Japan equips
split-phase electric power like USA, which can supply 200V by using reversed phase at the same time.
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
is unusual in having both 127 V and 220 V systems at 60 Hz and also permitting interchangeable plugs and sockets.
Saudi Arabia
Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in Western Asia. It covers the bulk of the Arabian Peninsula, and has a land area of about , making it the fifth-largest country in Asia, the second-largest in the Ara ...
and
Mexico
Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
have mixed voltage systems; in residential and light commercial buildings both countries use 127 volts, with 220 volts in commercial and industrial applications. The Saudi government approved plans in August 2010 to transition the country to a totally 230/400 volts system, but Mexico has no plans to transition.
Measuring voltage
A distinction should be made between the voltage at the point of supply (nominal voltage at the point of interconnection between the electrical utility and the user) and the voltage rating of the equipment (utilization or load 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 is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirab ...
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
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the ...
(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 and storms and other unusual conditions may cause even larger transient variations. 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 supply voltage is due more to historical reasons than optimization of the electric power 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 than a 120 V system to deliver a given amount of power because the current, and consequently the resistive loss, is lower. 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.
Many areas, such as the US, which use (nominally) 120 V, make use of
three-wire, split-phase 240 V systems to supply large appliances. In this system a 240 V supply has a centre-tapped neutral to give two 120 V supplies which can also supply 240 V to loads connected between the two line wires.
Three-phase
Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional neutral ...
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 2,400/4,160 V whereas 3,300 V is the common standard for 50 Hz systems.
Standardization
Until 1987, mains voltage in large parts of Europe, including Germany, Austria and Switzerland, was
while the UK used
. Standard ISO
IEC 60038
International Standard IEC 60038, ''IEC standard voltages'', defines a set of standard voltages for use in low voltage and high voltage AC and DC electricity supply systems.
Low voltage
Where two voltages are given below separated by "/", t ...
:1983 defined the new standard European voltage to be
.
From 1987 onwards, a step-wise shift towards
was implemented. From 2009 on, the voltage is permitted to be
. No change in voltage was required by either the Central European or the UK system, as both 220 V and 240 V fall within the lower 230 V tolerance bands (230 V ±6%). Some areas of the UK still have 250 volts for legacy reasons, but these also fall within the 10% tolerance band of 230 volts. In practice, this allowed countries to have supplied the same voltage (220 or 240 V), at least until existing supply transformers are replaced. Equipment (with the exception of
filament bulb
An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxidat ...
s) 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 V to 126 V (
RMS) (−5% to +5%). Historically 110 V, 115 V and 117 V have been used at different times and places in North America. Mains power is sometimes spoken of as 110 V; however, 120 V is the nominal voltage.
In 2000,
Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
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 and
British English
British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, "English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in England, or, more broadl ...
. In
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, the electrical power supply to households is at 100 and 200 V. Eastern and northern parts of
Honshū
, historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island sepa ...
(including
Tokyo
Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.46 ...
) and
Hokkaidō
is Japan, Japan's Japanese archipelago, second largest island and comprises the largest and northernmost Prefectures of Japan, prefecture, making up its own List of regions of Japan, region. The Tsugaru Strait separates Hokkaidō from Honshu; th ...
have a frequency of 50 Hz, whereas western Honshū (including Nagoya, Osaka, and Hiroshima),
Shikoku
is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), '' ...
,
Kyūshū
is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surround ...
and
Okinawa
is a Prefectures of Japan, prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 Square kilometre, km2 (880 sq mi).
...
operate at 60 Hz. The boundary between the two regions contains four back-to-back
high-voltage direct-current (HVDC) substations which interconnect the power between the two grid systems; these are
Shin Shinano
is the designation of a back-to-back high-voltage direct current (HVDC) facility in Japan which forms one of four frequency converter stations that link Japan's western and eastern power grids. The other three stations are at Higashi-Shimiz ...
,
Sakuma Dam
The is a dam on the Tenryū River, located on the border of Toyone, Kitashitara District, Aichi Prefecture on the island of Honshū, Japan. It is one of the tallest dams in Japan and supports a 350 MW hydroelectric power station. Nearby a f ...
,
Minami-Fukumitsu
is the name given to an HVDC back-to-back station for the interconnection of the power grids of western 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 mega ...
, and the
Higashi-Shimizu Frequency Converter
is the third facility in Japan for interconnecting the power grid of eastern Japan, which operates at 50 hertz, and that of western Japan, which operates at 60 hertz.
The Higashi-Shimizu Frequency Converter Station is operated by Chubu Electri ...
. To accommodate the difference, frequency-sensitive appliances marketed in Japan can often be switched between the two frequencies.
History
![Czestosciomierz-49](https://upload.wikimedia.org/wikipedia/commons/8/81/Czestosciomierz-49.9Hz.jpg)
The world's first public electricity supply was a
water wheel
A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a wheel (usually constructed from wood or metal), with a number of blades or buckets ...
driven system constructed in the small English town of
Godalming
Godalming is a market town and civil parish in southwest Surrey, England, around southwest of central London. It is in the Borough of Waverley, at the confluence of the Rivers Wey and Ock. The civil parish covers and includes the settlement ...
in 1881. It was an
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC) system using a Siemens alternator supplying power for both street lights and consumers at two voltages, 250 V for arc lamps, and 40 V for incandescent lamps.
The world's first large scale central plant—
Thomas Edison
Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventi ...
's
steam powered station at Holborn Viaduct in London—started operation in January 1882, providing
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...
(DC) at 110 V. The Holborn Viaduct station was used as a
proof of concept
Proof of concept (POC or PoC), also known as proof of principle, is a realization of a certain method or idea in order to demonstrate its feasibility, or a demonstration in principle with the aim of verifying that some concept or theory has prac ...
for the construction of the much larger
Pearl Street Station
Pearl Street Station was the first commercial central power plant in the United States. It was located at 255–257 Pearl Street in the Financial District of Manhattan, New York City, just south of Fulton Street on a site measuring . The statio ...
in
Manhattan
Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...
, the world's first permanent commercial central power plant. The Pearl Street Station also provided DC at 110 V, considered to be a "safe" voltage for consumers, beginning 4 September 1882.
AC systems started appearing in the US in the mid-1880s, using higher distribution voltage stepped down via
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s to the same 110 V customer utilization voltage that Edison used. In 1883 Edison patented a
three–wire distribution system to allow DC generation plants to serve a wider radius of customers to save on copper costs. By connecting two groups of 110 V lamps in series more load could be served by the same size conductors run with 220 V between them; a neutral conductor carried any imbalance of current between the two sub-circuits. AC circuits adopted the same form during the
war of the currents
The war of the currents was a series of events surrounding the introduction of competing electric power transmission systems in the late 1880s and early 1890s. It grew out of two lighting systems developed in the late 1870s and early 1880s; arc ...
, allowing lamps to be run at around 110 V and major appliances to be connected to 220 V. Nominal voltages gradually crept upward to 112 V and 115 V, or even 117 V. After
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
the standard voltage in the U.S. became 117 V, but many areas lagged behind even into the 1960s. In 1954, the
American National Standards Institute (ANSI) published C84.1 “American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz)”. This standard established 120 volt nominal system and two ranges for service voltage and utilization voltage variations. Today, virtually all American homes and businesses have access to 120 and 240 V at 60 Hz. Both voltages are available on the three wires (two "hot" legs of opposite phase and one "neutral" leg).
In 1899, the Berliner Elektrizitäts-Werke (BEW), a
Berlin
Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...
electrical utility, decided to greatly increase its distribution capacity by switching to 220 V nominal distribution, taking advantage of the higher voltage capability of newly developed 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 V system became common. North American practice remained with voltages near 110 V for lamps.
In the first decade after the introduction of alternating current in the US (from the early 1880s to about 1893) a variety of different frequencies were used, with each electric provider setting their own, so that no single one prevailed. The most common frequency was 133⅓ Hz. The rotation speed of induction generators and motors, the efficiency of transformers, and flickering of carbon arc lamps all played a role in frequency setting. Around 1893 the
Westinghouse Electric Company
Westinghouse Electric Company LLC is an American nuclear power company formed in 1999 from the nuclear power division of the original Westinghouse Electric Corporation. It offers nuclear products and services to utilities internationally, includi ...
in the United States and
AEG in Germany decided to standardize their generation equipment on 60 Hz and 50 Hz respectively, eventually leading to most of the world being supplied at one of these two frequencies. Today most 60 Hz systems deliver nominal 120/240 V, and most 50 Hz nominally 230 V. The significant exceptions are in Brazil, which has a synchronized 60 Hz grid with both 127 V and 220 V as standard voltages in different regions,
and
Japan, which has two frequencies: 50 Hz for East Japan and 60 Hz for West Japan.
Voltage regulation
To maintain the voltage at the customer's service within the acceptable range, electrical distribution utilities use
regulating equipment at
electrical substations or along the distribution line. At a substation, the step-down
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
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 kilometres) rural distribution circuits, automatic voltage regulators may be mounted on poles of the distribution line. These are
autotransformer
An autotransformer is an electrical transformer with only one winding. The " auto" (Greek for "self") prefix refers to the single coil acting alone, not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act a ...
s, again, with on-load tap changers 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 used only to adjust the long-term average voltage at the service and not to regulate the voltage seen by the utility customer.
Power quality
The stability of the voltage and frequency supplied to customers varies among countries and regions. "Power quality" is a term describing the degree of deviation from the nominal supply voltage and frequency. Short-term surges and drop-outs affect sensitive electronic equipment such as computers and
flat panel display
A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipment.
Flat-panel displays are thin, lightweight, provide better l ...
s. Longer-term power outages,
brown-outs and
black outs and low reliability of supply generally increase costs to customers, who may have to invest in
uninterruptible power supply
An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power syste ...
or stand-by
generator
Generator may refer to:
* Signal generator, electronic devices that generate repeating or non-repeating electronic signals
* Electric generator, a device that converts mechanical energy to electrical energy.
* Generator (circuit theory), an eleme ...
sets to provide power when the utility supply is unavailable or unusable. Erratic power supply may be a severe economic handicap to businesses and public services which rely on electrical machinery, illumination, climate control and computers. Even the best quality power system may have breakdowns or require servicing. As such, companies, governments and other organizations sometimes have backup generators at sensitive facilities, to ensure that power will be available even in the event of a power outage or black out.
Power quality can also be affected by distortions of the current or voltage waveform in the form of
harmonics
A harmonic is a wave with a frequency that is a positive integer multiple of the '' fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', ...
of the fundamental (supply) frequency, or non-harmonic
(inter)modulation distortion such as that caused by
RFI or EMI interference. In contrast, harmonic distortion is usually caused by conditions of the load or generator. In multi-phase power, phase shift distortions caused by imbalanced loads can occur.
See also
*
Energy meter
file:Hydro quebec meter.JPG, North American domestic analog signal, analog electricity meter.
file:Transparent Electricity Meter found in Israel.JPG, Electricity meter with transparent plastic case (Israel)
file:Hydro Quebec meter solid state.j ...
References
{{DEFAULTSORT:Mains Electricity
Electric power