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An electrical grid is an interconnected network for
electricity delivery Electricity delivery is the process that starts after generation of electricity in the power station A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the ...
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 Transmission: Background and Policy Issues. The Capital.Net, Government Series. Pp. 1-42. *
power station A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation A generation is "all of the people born and living Living or The Living may refer to: ...

power station
s: often located near energy and away from heavily populated areas *
electrical substation A substation is a part of an electrical Electricity generation, generation, electric power transmission, transmission, and electric power distribution, distribution system. Substations transform voltage from high to low, or the reverse, or per ...

electrical substation
s to step
voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

voltage
up or down *
electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived as a result of movement of electrically charged particles. When used loosely, ''electrical energy'' refers to energy that has been convert ...
to carry power long distances *
electric power distribution Electric power distribution is the final stage in the delivery Delivery may refer to: *Delivery (commerce), of goods, e.g.: **Pizza delivery **Milk delivery Film and television *Delivering (film), ''Delivering'' (film), a 1993 short film by Todd ...
to individual customers, where voltage is stepped down again to the required service voltage(s). Grids are nearly always synchronous, meaning all distribution areas operate with
three phase Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, Electric power transmission, transmission, and Electric power distribution, distribution. It is a type of polyphase system emplo ...

three phase
alternating current Alternating current (AC) is an electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'natu ...
(AC) frequencies synchronized (so that voltage swings occur at almost the same time). This allows transmission of AC power throughout the area, connecting a large number of electricity generators and consumers and potentially enabling more efficient electricity markets and redundant generation. The combined transmission and distribution network is part of electricity delivery, known as the "power grid" in
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
, or just "the grid". In the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shorth ...

United Kingdom
,
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

India
,
Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa East Africa or Eastern Africa is the eastern subregion of the Africa Africa is the world's second-larges ...

Tanzania
,
Myanmar Myanmar, ); UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, John ...

Myanmar
,
Malaysia Malaysia ( ; ) is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical southeastern subregion of Asia, consisting of the regions ...

Malaysia
and
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
, the network is known as the National Grid. Although electrical grids are widespread, , 1.4 billion people worldwide were not connected to an electricity grid. As
electrification Electrification is the process of powering by electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, mo ...

electrification
increases, the number of people with access to grid electricity is growing. About 840 million people (mostly in Africa) had no access to grid electricity in 2017, down from 1.2 billion in 2010. Electrical grids can be prone to malicious intrusion or attack; thus, there is a need for
electric grid security Electric grid security in the US refer to the activities that utilities, regulators, and other stakeholders play in securing the national electricity grid. The American electrical grid is going through one of the largest changes in its history, whic ...
. Also as electric grids modernize and introduce computer technology, cyber threats start to become a security risk. Particular concerns relate to the more complex computer systems needed to manage grids.


History

Early electric energy was produced near the device or service requiring that energy. In the 1880s, electricity competed with steam, hydraulics, and especially
coal gas Coal gas is a flammable gaseous fuel Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Many fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures there ...

coal gas
. Coal gas was first produced on customer's premises but later evolved into
gasification Gasification is a process that converts biomass Biomass is plant or animal material used as fuel to produce electricity or heat. Examples are wood, energy crops and waste from forests, yards, or farms. Since biomass technically can be used as ...

gasification
plants that enjoyed
economies of scale 330px, As quantity of production increases from Q to Q2, the average cost of each unit decreases from C to C1. LRAC is the long-run average cost In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their sca ...

economies of scale
. In the industrialized world, cities had networks of piped gas, used for lighting. But gas lamps produced poor light, wasted heat, made rooms hot and smoky, and gave off
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
and
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
. They also posed a fire hazard. In the 1880s electric lighting soon became advantageous compared to gas lighting. Electric utility companies established central stations to take advantage of economies of scale and moved to centralized power generation, distribution, and system management.Borberly, A. and Kreider, J. F. (2001). Distributed Generation: The Power Paradigm for the New Millennium. CRC Press, Boca Raton, FL. 400 pgs. After 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 l ...
was settled in favor of
AC power Power (physics), Instantaneous power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductors and capacitors may result in periodic reversal ...
, with long-distance power transmission it became possible to interconnect stations to balance the loads and improve load factors. Historically, transmission and distribution lines were owned by the same company, but starting in the 1990s, many countries have liberalized the regulation of the
electricity market In economic terms, electricity is a commodity capable of being bought, sold, and traded. An electricity market, also power exchange or PX, is a system enabling purchases, through bids to buy; sales, through offers to sell. Bids and offers use sup ...
in ways that have led to the separation of the electricity transmission business from the distribution business. In the United Kingdom,
Charles Merz Charles Hesterman Merz (5 October 1874 – 14 or 15 October 1940) was a British electrical engineer who pioneered the use of high-voltage three-phase electricity distribution, AC power distribution in the United Kingdom, building a system in the ...
, of the
Merz & McLellan Merz and McLellan was a leading United Kingdom, British electrical engineering consultancy based in Newcastle upon Tyne, Newcastle. History The firm was founded by Charles Hesterman Merz, Charles Merz and William McLellan (Scottish electrical engi ...
consulting partnership, built the
Neptune Bank Power Station Neptune Bank Power Station was a coal-fired power station A coal-fired power station or coal power plant is a thermal power station A thermal power station is a power station in which heat energy is converted to electricity. Typically, ...
near
Newcastle upon Tyne Newcastle upon Tyne ( , ), often simply Newcastle, is the largest city A city is a large .Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedi ...

Newcastle upon Tyne
in 1901, and by 1912 had developed into the largest integrated power system in Europe. Merz was appointed head of a Parliamentary Committee and his findings led to the Williamson Report of 1918, which in turn created the Electricity Supply Bill of 1919. The bill was the first step towards an integrated electricity system. The Electricity (Supply) Act of 1926 led to the setting up of the National Grid. The
Central Electricity Board The United Kingdom Central Electricity Board was established by the Electricity (Supply) Act 1926. It had the duty to supply electricity to authorised electricity undertakers, to determine which power stations would be 'selected' stations to gen ...
standardized the nation's electricity supply and established the first synchronized AC grid, running at 132 kilovolts and 50
Hertz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action ...

Hertz
. This started operating as a national system, the National Grid, in 1938. In the United States in the 1920s, utilities formed joint-operations to share peak load coverage and backup power. In 1934, with the passage of the Public Utility Holding Company Act (USA), electric utilities were recognized as public goods of importance and were given outlined restrictions and regulatory oversight of their operations. The
Energy Policy Act of 1992 The Energy Policy Act, effective October 24, 1992, (102nd Congress H.R.776.ENR, abbreviated as EPACT92) is a United States government The federal government of the United States (U.S. federal government) is the national government of the U ...
required transmission line owners to allow electric generation companies open access to their networkMazer, A. (2007). Electric Power Planning for Regulated and Deregulated Markets. John, Wiley, and Sons, Inc., Hoboken, NJ. 313pgs. and led to a restructuring of how the electric industry operated in an effort to create competition in power generation. No longer were electric utilities built as vertical monopolies, where generation, transmission and distribution were handled by a single company. Now, the three stages could be split among various companies, in an effort to provide fair access to high voltage transmission.. (2001). Glover J. D., Sarma M. S., Overbye T. J. (2010) Power System and Analysis 5th Edition. Cengage Learning. Pg 10. The
Energy Policy Act of 2005 The Energy Policy Act of 2005 () is a federal law signed by President George W. Bush on August 8, 2005, at Sandia National Laboratories in Albuquerque, New Mexico. The act, described by proponents as an attempt to combat growing energy problems, ...
allowed incentives and loan guarantees for alternative energy production and advance innovative technologies that avoided
greenhouse emissions Greenhouse gas emissions are emissions of greenhouse gases A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ ( ...
. In France,
electrification Electrification is the process of powering by electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, mo ...

electrification
began in the 1900s, with 700
communes A commune is an intentional community of people sharing living spaces, interests, values, beliefs, and often property, possessions, and resources in common. In some communes, the people also share common Employment, work, income, or assets. ...

communes
in 1919, and 36,528 in 1938. At the same time, these close networks began to interconnect: Paris in 1907 at 12 kV, the Pyrénées in 1923 at 150 kV, and finally almost all of the country interconnected by 1938 at 220 kV. In 1946, the grid was the world's most dense. That year the state nationalised the industry, by uniting the private companies as
Électricité de France Électricité de France S.A. (literally ''Electricity of France''), commonly known as EDF, is a French multinational electric utility company, largely owned by the French state. Headquartered in Paris Paris () is the Capital city, capita ...
. The frequency was standardised at 50 Hz, and the 225 kV network replaced 110 kV and 120 kV. Since 1956, service voltage has been standardised at 220/380 V, replacing the previous 127/220 V. During the 1970s, the 400 kV network, the new European standard, was implemented. In China, electrification began in the 1950s. In August 1961, the electrification of the Baoji-Fengzhou section of the was completed and delivered for operation, becoming China's first
electrified railway (the "Skokie Swift"), shown shortly before the conversion to third rail operation in September 2004. A railway electrification system supplies electric power to Rail transport, railway trains and trams without an on-board Prime mover (locomotive ...
. From 1958 to 1998, China's electrified railway reached 6,200 miles (10,000 kilometers). As of the end of 2017, this number has reached 54,000 miles (87,000 kilometers). In the current
railway electrification system A railway electrification system supplies electric power Electric power is the rate, per unit time, at which electrical energy Electrical energy is energy derived as a result of movement of electrically charged particles. When used loos ...

railway electrification system
of China
State Grid Corporation of China
is an important power supplier. In 2019, it completed the power supply project of China's important electrified railways in its operating areas, such as Jingtong Railway,
Haoji Railway The Haoji Railway (), fully known as Kholbolji/Haolebaoji to Ji'an railway (), formerly known as Menghua Railway (West Inner Mongolia to Central China), is a freight-dedicated railway in China. It runs from Haolebaoji South railway station in Uxin ...
, Zhengzhou–Wanzhou high-speed railway, et cetera, providing power supply guarantee for 110 traction stations, and its cumulative power line construction length reached 6,586 kilometers.


Components


Generation

Electricity generation is the process of generating
electric power Electric power is the rate, per unit time, at which electrical energy Electrical energy is energy derived as a result of movement of electrically charged particles. When used loosely, ''electrical energy'' refers to energy that has been conve ...
from sources of
primary energy Primary energy (PE) is an energy In , energy is the that must be to a or to perform on the body, or to it. Energy is a ; the law of states that energy can be in form, but not created or destroyed. The unit of measurement in the ...
typically at
power station A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation A generation is "all of the people born and living Living or The Living may refer to: ...

power station
s. Usually this is done with
electromechanical In engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad ran ...
generators driven by
heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do work (physics), mechanical work. It does this by bringing a working substance from a higher state temperature to ...

heat engine
s or the
kinetic energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
of water or wind. Other energy sources include solar
photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially u ...
and
geothermal power Geothermal power is electrical power generated from geothermal energy Geothermal energy is the thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The geothermal energy ...
. The sum of the power outputs of generators on the grid is the production of the grid, typically measured in
gigawatts The watt (symbol: W) is a unit of Power (physics), power or radiant flux. In the International System of Units (SI), it is defined as a SI derived unit, derived unit of (in SI base units) 1 kg⋅m2⋅s−3 or, equivalently, 1 joule per second. I ...
(GW).


Transmission

Electric power transmission is the bulk movement of
electrical energy Electrical energy is energy derived as a result of movement of electrically charged particles. When used loosely, ''electrical energy'' refers to energy that has been converted ''from'' electric potential energy. This energy is supplied by the comb ...
from a generating site, via a web of interconnected lines, to an
electrical substation A substation is a part of an electrical Electricity generation, generation, electric power transmission, transmission, and electric power distribution, distribution system. Substations transform voltage from high to low, or the reverse, or per ...

electrical substation
, from which is connected to the distribution system. This networked system of connections is distinct from the local wiring between high-voltage substations and customers. Because the power is often generated far from where it is consumed, the transmission system can cover great distances. For a given amount of power, transmission efficiency is greater at higher voltages and lower amperages. Therefore voltages are stepped up at the generating station, at stepped down at local substations for distribution to customers. Most transmission is
three-phase In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating voltages that are offset in time by one-third of the period. A three-phase system may be arranged in delta (∆) or star (Y) (also ...
. Three phase, compared to single phase, can deliver much more power for a given amount of wire, since the neutral and ground wires are shared. Further, three-phase generators and motors are more efficient than their single-phase counterparts. However for conventional conductors one of the main losses are resistive losses which are a square law on current, and depend on distance. High voltage AC transmission lines can lose 1-4% per hundred miles. However,
high-voltage direct current A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
can have half the losses of AC. Over very long distances, these efficiencies can offset the additional cost of the required AC/DC converter stations at each end. Transmission networks are complex with redundant pathways. The physical layout is often forced by what land is available and its geology. Most transmission grids offer the reliability that more complex ''mesh networks'' provide. Redundancy allows line failures to occur and power is simply rerouted while repairs are done.


Substations

Substations may perform many different functions but usually transform voltage from low to high (step up) and from high to low (step down). Between the generator and the final consumer, the voltage may be transformed several times. The three main types of substations, by function, are: * Step-up substation: these use
transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current in any one coil of the transformer produces a varying magnetic flux ...

transformer
s to raise the voltage coming from the generators and power plants so that power can be transmitted long distances more efficiently, with smaller currents. * Step-down substation: these transformers lower the voltage coming from the transmission lines which can be used in industry or sent to a distribution substation. * Distribution substation: these transform the voltage lower again for the distribution to end users. Aside from transformers, other major components or functions of substations include: *
Circuit breaker A circuit breaker is an electrical safety device designed to protect an electrical circuit An electrical network is an interconnection of electrical component An electronic component is any basic discrete device or physical entity ...

Circuit breaker
s: used to automatically break a circuit and isolate a fault in the system. *
Switch In electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics The field of electronics is a branch of p ...

Switch
es: to control the flow of electricity, and isolate equipment. * The substation
busbar In , a busbar (also bus bar) is a metallic strip or bar, typically housed inside , , and for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment i ...

busbar
: typically a set of three conductors, one for each phase of current. The substation is orgranized around the buses, and they are connected to incoming lines, transformers, protection equipment, switches, and the outgoing lines. *
Lightning arrester A lightning arrester (alternative spelling lightning arrestor) (also called lightning diverter) is a device used on electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy de ...
s *
Capacitor A capacitor is a device that stores electric charge in an electric field. It is a passivity (engineering), passive electronic component with two terminal (electronics), terminals. The effect of a capacitor is known as capacitance. While som ...

Capacitor
s for
power factor In electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics The field of electronics is a branch of ph ...
correction


Electric power distribution

Distribution is the final stage in the delivery of power; it carries electricity from the transmission system to individual consumers. Substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between and . Primary distribution lines carry this medium voltage power to
distribution transformer A distribution transformer or service transformer is a transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current ...
s located near the customer's premises. Distribution transformers again lower the voltage to the
utilization voltage Mains electricity (Commonwealth English The use of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become ...
. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the subtransmission level. Distribution networks are divided into two types, radial or network. In cities and towns of North America, the grid tends to follow the classic ''radially fed'' design. A substation receives its power from the transmission network, the power is stepped down with a transformer and sent to a
bus trolleybus in Toronto Toronto is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a recorded population of 2,731,571 in 2016, it is the List of the 100 largest municipalities in Canada by p ...

bus
from which feeders fan out in all directions across the countryside. These feeders carry three-phase power, and tend to follow the major streets near the substation. As the distance from the substation grows, the fanout continues as smaller laterals spread out to cover areas missed by the feeders. This tree-like structure grows outward from the substation, but for reliability reasons, usually contains at least one unused backup connection to a nearby substation. This connection can be enabled in case of an emergency, so that a portion of a substation's service territory can be alternatively fed by another substation.


Storage

''Grid energy storage'' (also called ''large-scale energy storage'') is a collection of methods used for
energy storage Energy storage is the capture of energy In physics, energy is the physical quantity, quantitative physical property, property that must be #Energy transfer, transferred to a physical body, body or physical system to perform Work (thermody ...

energy storage
on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inexpensive (especially from intermittent power sources such as
renewable electricity Renewable energy is useful energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, also known as a flow resource, is a natural resource which will replenish to replace the portio ...
from
wind power Wind power or wind energy is the use of wind turbine A wind turbine is a device that converts Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination A religious denomination ...

wind power
,
tidal power#REDIRECT Tidal power Tidal power or tidal energy is harnessed by converting energy from tide (U.S.), low tide occurs roughly at moonrise and high tide with a high Moon, corresponding to the simple gravity model of two tidal bulges; at most ...
and
solar power Solar power is the conversion of renewable energy Renewable energy is energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, also known as a flow resource, is a natural re ...

solar power
) or when demand is low, and later returned to the grid when demand is high, and electricity prices tend to be higher. , the largest form of grid energy storage is dammed
hydroelectricity Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water Water (chemical formula H2O) is ...
, with both conventional hydroelectric generation as well as
pumped storage hydroelectricity Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectricity, hydroelectric energy storage used by electric power systems for load balancing (electrical power), load balancing. The method s ...
. Developments in battery storage have enabled commercially viable projects to store energy during peak production and release during peak demand, and for use when production unexpectedly falls giving time for slower responding resources to be brought online. Two alternatives to grid storage are the use of
peaking power plant Peaking power plants, also known as peaker plants, and occasionally just "peakers", are power plantPower Station or The Power Station may refer to: * Power station, a facility for the generation of electricity Music * The Power Station (band), a 1 ...
s to fill in supply gaps and
demand response Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until recently electric energy could not be easily stored, so utilities have traditionally matched demand ...

demand response
to shift load to other times.


Functionalities


Demand

The demand, or load on an electrical grid is the total electrical power being removed by the users of the grid. The graph of the demand over time is called the ''demand curve''.
Baseload The baseload (also base load) on a grid is the minimum level of demand on an electrical grid An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover who ...
is the minimum load on the grid over any given period,
peak demand Peak demand on an electrical grid An electrical grid is an interconnected network for 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. ...
is the maximum load. Historically, baseload was commonly met by equipment that was relatively cheap to run, that ran continuously for weeks or months at a time, but globally this is becoming less common. The extra peak demand requirements are sometimes produced by expensive peaking plants that are generators optimised to come on-line quickly but these too are becoming less common.


Voltage

Grids are designed to supply electricity to their customers at largely constant voltages. This has to be achieved with varying demand, variable
reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a Bowling ball#Coverstock technology, bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reacti ...
loads, and even nonlinear loads, with electricity provided by generators and distribution and transmission equipment that are not perfectly reliable. Often grids use
tap changer A tap changer is a mechanism in transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current in any one coil of the t ...
s on transformers near to the consumers to adjust the voltage and keep it within specification.


Frequency

In a synchronous grid all the generators must run at the same frequency, and must stay very nearly in phase with each other and the grid. Generation and consumption must be balanced across the entire grid, because energy is consumed as it is produced. For rotating generators, a local
governor A governor is, in most cases, a public official with the power to govern the Executive (government), executive branch of a non-sovereign or sub-national level of government, ranking under the head of state. In federations, ''governor'' may be t ...
regulates the driving torque, maintaining almost constant rotation speed as loading changes. Energy is stored in the immediate short term by the rotational kinetic energy of the generators. Although the speed is kept largely constant, small deviations from the nominal system frequency are very important in regulating individual generators and are used as a way of assessing the equilibrium of the grid as a whole. When the grid is lightly loaded the grid frequency runs above the nominal frequency, and this is taken as an indication by Automatic Generation Control systems across the network that generators should reduce their output. Conversely, when the grid is heavily loaded, the frequency naturally slows, and governors adjust their generators so that more power is output (
droop speed controlDroop speed control is a control mode used for AC electrical power generators, whereby the power output of a generator reduces as the line frequency increases. It is commonly used as the speed control mode of the governor A governor is, in most ca ...
). When generators have identical droop speed control settings it ensures that multiple parallel generators with the same settings share load in proportion to their rating. In addition, there's often central control, which can change the parameters of the AGC systems over timescales of a minute or longer to further adjust the regional network flows and the operating frequency of the grid. For timekeeping purposes, the nominal frequency will be allowed to vary in the short term, but is adjusted to prevent line-operated clocks from gaining or losing significant time over the course of a whole 24 hour period. An entire synchronous grid runs at the same frequency, neighbouring grids would not be synchronised even if they run at the same nominal frequency.
High-voltage direct current A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
lines or
variable-frequency transformer A variable-frequency transformer (VFT) is used to transmit electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In p ...
s can be used to connect two alternating current interconnection networks which are not synchronized with each other. This provides the benefit of interconnection without the need to synchronize an even wider area. For example, compare the wide area synchronous grid map of Europe with the map of HVDC lines.


Capacity and firm capacity

The sum of the maximum power outputs (
nameplate capacityNameplate capacity, also known as the rated capacity, nominal capacity, installed capacity, or maximum effect, is the intended full-load sustained output of a facility such as a power plant,
) of the generators attached to an electrical grid might be considered to be the capacity of the grid. However, in practice, they are never run flat out simultaneously. Typically, some generators are kept running at lower output powers (
spinning reserve In grid (electricity), electricity networks, the operating reserve is the generating capacity available to the independent system operator, system operator within a short interval of time to meet demand in case a electrical generator, generator go ...
) to deal with failures as well as variation in demand. In addition generators can be off-line for maintenance or other reasons, such as availability of energy inputs (fuel, water, wind, sun etc.) or pollution constraints. ''Firm capacity'' is the maximum power output on a grid that is immediately available over a given time period, and is a far more useful figure.


Production

Most grid codes specify that the load is shared between the generators in
merit order The merit order is a way of ranking available sources of energy, especially electrical generation, based on ascending order of price (which may reflect the order of their short-run marginal costs of production) and sometimes pollution, together wit ...
according to their
marginal cost In economics Economics () is the social science that studies how people interact with value; in particular, the Production (economics), production, distribution (economics), distribution, and Consumption (economics), consumption of goods a ...

marginal cost
(i.e. cheapest first) and sometimes their environmental impact. Thus cheap electricity providers tend to be run flat out almost all the time, and the more expensive producers are only run when necessary.


Handling failure

Failures are usually associated with generators or power transmission lines tripping circuit breakers due to faults leading to a loss of generation capacity for customers, or excess demand. This will often cause the frequency to reduce, and the remaining generators will react and together attempt to stabilize above the minimum. If that is not possible then a number of scenarios can occur. A large failure in one part of the grid—unless quickly compensated for—can cause current to re-route itself to flow from the remaining generators to consumers over transmission lines of insufficient capacity, causing further failures. One downside to a widely connected grid is thus the possibility of
cascading failure A cascading failure is a process in a system of interconnected parts in which the failure of one or few parts can trigger the failure of other parts and so on. Such a failure may happen in many types of systems, including power transmission, comp ...
and widespread
power outage A power outage (also called a powercut, a power out, a power blackout, a power failure, a power loss, or a blackout) is the loss of the electrical power Electric power is the rate, per unit time, at which electrical energy Electrical en ...
. A central authority is usually designated to facilitate communication and develop protocols to maintain a stable grid. For example, the
North American Electric Reliability Corporation The North American Electric Reliability Corporation (NERC) is a nonprofit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a ...
gained binding powers in the United States in 2006, and has advisory powers in the applicable parts of Canada and Mexico. The U.S. government has also designated
National Interest Electric Transmission Corridor A National Interest Electric Transmission Corridor (NIETC) corridor is a geographic region designated by the United States Department of Energy The United States Department of Energy (DOE) is a cabinet-level department of the United States ...
s, where it believes transmission bottlenecks have developed.


Brownout

A ''brownout'' is an intentional or unintentional drop in voltage in an electrical power supply system. Intentional brownouts are used for load reduction in an emergency. The reduction lasts for minutes or hours, as opposed to short-term voltage sag (or dip). The term brownout comes from the dimming experienced by incandescent lighting when the voltage sags. A voltage reduction may be an effect of disruption of an electrical grid, or may occasionally be imposed in an effort to reduce load and prevent a
power outage A power outage (also called a powercut, a power out, a power blackout, a power failure, a power loss, or a blackout) is the loss of the electrical power Electric power is the rate, per unit time, at which electrical energy Electrical en ...
, known as a Power outage, blackout.


Blackout

A ''power outage'' (also called a ''power cut'', a ''power out'', a ''power blackout'', ''power failure'' or a ''blackout'') is a loss of the electric power to a particular area. Power failures can be caused by faults at power stations, damage to electric transmission lines, Electrical substation, substations or other parts of the electricity distribution, distribution system, a short circuit, Cascading failure#Cascading failure in power transmission, cascading failure, fuse (electrical), fuse or circuit breaker operation, and human error. Power failures are particularly critical at sites where the environment and public safety are at risk. Institutions such as hospitals, sewage treatment plants, mining, mines, shelters and the like will usually have backup power sources such as emergency power system, standby generators, which will automatically start up when electrical power is lost. Other critical systems, such as telecommunication, are also required to have emergency power. The battery room of a telephone exchange usually has arrays of Lead–acid battery, lead–acid batteries for backup and also a socket for connecting a generator during extended periods of outage.


Load shedding

Electrical generation and transmission systems may not always meet peak demand requirements— the greatest amount of electricity required by all utility customers within a given region. In these situations, overall demand must be lowered, either by turning off service to some devices or cutting back the supply voltage (brownout (electricity), brownouts), in order to prevent uncontrolled service disruptions such as power outages (widespread blackouts) or equipment damage. Utilities may impose load shedding on service areas via targeted blackouts, rolling blackouts or by agreements with specific high-use industrial consumers to turn off equipment at times of system-wide peak demand.


Black start

A ''black start'' is the process of restoring an electric power station or a part of an electric grid to operation without relying on the external transmission network, electric power transmission network to recover from a total or partial shutdown.Knight, U.G. ''Power Systems in Emergencies - From Contingency Planning to Crisis Management '' John Wiley & Sons 2001 section 7.5 The 'Black Start' Situation Normally, the electric power used within the plant is provided from the station's own generators. If all of the plant's main generators are shut down, station service power is provided by drawing power from the grid through the plant's transmission line. However, during a wide-area outage, off-site power from the grid is not available. In the absence of grid power, a so-called black start needs to be performed to Bootstrapping#Electric power grid, bootstrap the power grid into operation. To provide a black start, some power stations have small diesel generators, normally called the ''black start diesel generator'' (BSDG), which can be used to start larger generators (of several megawatts capacity), which in turn can be used to start the main power station generators. Generating plants using steam turbines require station service power of up to 10% of their capacity for boiler feedwater pumps, boiler forced-draft combustion air blowers, and for fuel preparation. It is uneconomical to provide such a large standby capacity at each station, so black-start power must be provided over designated tie lines from another station. Often hydroelectric power plants are designated as the black-start sources to restore network interconnections. A hydroelectric station needs very little initial power to start (just enough to open the intake gates and provide excitation (magnetic), excitation current to the generator field coils), and can put a large block of power on line very quickly to allow start-up of fossil-fuel or nuclear stations. Certain types of combustion turbine can be configured for black start, providing another option in places without suitable hydroelectric plants. In 2017 a utility in Southern California has successfully demonstrated the use of a battery energy storage system to provide a black start, firing up a combined cycle gas turbine from an idle state.


Scale


Microgrid

A microgrid is a local grid that is usually part of the regional wide-area synchronous grid but which can disconnect and operate autonomously. It might do this in times when the main grid is affected by outages. This is known as islanding, and it might run indefinitely on its own resources. Compared to larger grids, microgrids typically use a lower voltage distribution network and distributed generators. Microgrids may not only be more resilient, but may be cheaper to implement in isolated areas. A design goal is that a local area produces all of the energy it uses. Example implementations include: * Hajjah and Lahij, Lahj, Yemen: community-owned solar microgrids. * Île d'Yeu pilot program: sixty-four solar panels with a peak capacity of 23.7 kW on five houses and a battery with a storage capacity of 15 kWh. * Les Anglais, Haiti: includes energy theft detection. * Mpeketoni, Kenya: a community-based diesel-powered micro-grid system. * Stone Edge Farm Winery: micro-turbine, fuel-cell, multiple battery, hydrogen electrolyzer, and PV enabled winery in Sonoma, California.


Wide area synchronous grid

A wide area synchronous grid, also known as an "interconnection" in North America, directly connects many generators delivering AC power with the same relative ''frequency'' to many consumers. For example, there are four major interconnections in North America (the Western Interconnection, the Eastern Interconnection, the Quebec Interconnection and the Texas Interconnection). In Europe Synchronous grid of Continental Europe, one large grid connects most of continental Europe. A ''wide area synchronous grid'' (also called an "interconnection" in North America) is an electrical grid at a regional scale or greater that operates at a synchronized frequency and is electrically tied together during normal system conditions. These are also known as synchronous zones, the largest of which is the synchronous grid of Continental Europe (ENTSO-E) with 667 
gigawatts The watt (symbol: W) is a unit of Power (physics), power or radiant flux. In the International System of Units (SI), it is defined as a SI derived unit, derived unit of (in SI base units) 1 kg⋅m2⋅s−3 or, equivalently, 1 joule per second. I ...
(GW) of generation, and the widest region served being that of the IPS/UPS system serving countries of the former Soviet Union. Synchronous grids with ample capacity facilitate
electricity market In economic terms, electricity is a commodity capable of being bought, sold, and traded. An electricity market, also power exchange or PX, is a system enabling purchases, through bids to buy; sales, through offers to sell. Bids and offers use sup ...
trading across wide areas. In the ENTSO-E in 2008, over 350,000 megawatt hours were sold per day on the European Energy Exchange (EEX). Each of the interconnects in North America are run at a nominal 60 Hz, while those of Europe run at 50 Hz. Neighbouring interconnections with the same frequency and standards can be synchronized and directly connected to form a larger interconnection, or they may share power without synchronization via high-voltage direct current power transmission lines (DC ties), or with variable-frequency transformers (VFTs), which permit a controlled flow of energy while also functionally isolating the independent AC frequencies of each side. The benefits of synchronous zones include pooling of generation, resulting in lower generation costs; pooling of load, resulting in significant equalizing effects; common provisioning of reserves, resulting in cheaper primary and secondary reserve power costs; opening of the market, resulting in possibility of long-term contracts and short term power exchanges; and mutual assistance in the event of disturbances. One disadvantage of a wide-area synchronous grid is that problems in one part can have repercussions across the whole grid. For example, in 2018 Kosovo used more power than it generated due to a dispute with Serbia, leading to the phase across the whole synchronous grid of Continental Europe lagging behind what it should have been. The frequency dropped to 49.996 Hz. This caused certain kinds of clocks to become six minutes slow. File:ElectricityUCTE.svg, The synchronous grids of Europe File:NERC-map-en.svg, The two major and three minor interconnections of North America File:Wide area synchronous grid (Eurasia, Mediterranean).png, Major WASGs around the world


Super grid

A ''super grid'' or ''supergrid'' is a wide-area transmission network that is intended to make possible the trade of high volumes of electricity across great distances. It is sometimes also referred to as a ''mega grid''. Super grids can support a global energy transition by smoothing local fluctuations of wind energy and solar energy. In this context they are considered as a key technology to Climate change mitigation, mitigate global warming. Super grids typically use
High-voltage direct current A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
(HVDC) to transmit electricity long distances. The latest generation of HVDC power lines can transmit energy with losses of only 1.6% per 1000 km. Electric utilities between regions are many times interconnected for improved economy and reliability. Electrical interconnectors allow for economies of scale, allowing energy to be purchased from large, efficient sources. Utilities can draw power from generator reserves from a different region to ensure continuing, reliable power and diversify their loads. Interconnection also allows regions to have access to cheap bulk energy by receiving power from different sources. For example, one region may be producing cheap hydro power during high water seasons, but in low water seasons, another area may be producing cheaper power through wind, allowing both regions to access cheaper energy sources from one another during different times of the year. Neighboring utilities also help others to maintain the overall system frequency and also help manage tie transfers between utility regions. Electricity Interconnection Level (EIL) of a grid is the ratio of the total interconnector power to the grid divided by the installed production capacity of the grid. Within the EU, it has set a target of national grids reaching 10% by 2020, and 15% by 2030.


Trends


Demand response

Demand response is a grid management technique where retail or wholesale customers are requested or incentivised either electronically or manually to reduce their load. Currently, transmission grid operators use demand response to request load reduction from major energy users such as industrial plants. Technologies such as smart metering can encourage customers to use power when electricity is plentiful by allowing for variable pricing.


Aging infrastructure

Despite the novel institutional arrangements and network designs of the electrical grid, its power delivery infrastructures suffer aging across the developed world. Contributing factors to the current state of the electric grid and its consequences include: * Aging equipment – older equipment has higher failure rates, leading to customer interruption rates affecting the economy and society; also, older assets and facilities lead to higher inspection Maintenance, repair, and operations, maintenance costs and further Maintenance, repair, and operations, repair and Renovation, restoration costs. * Obsolete system layout – older areas require serious additional substation sites and Right-of-way (transportation), rights-of-way that cannot be obtained in the current area and are forced to use existing, insufficient facilities. * Outdated engineering – traditional tools for power delivery planning and engineering are ineffective in addressing current problems of aged equipment, obsolete system layouts, and modern deregulated loading levels. * Old cultural value – planning, engineering, operating of system using concepts and procedures that worked in vertically integrated industry exacerbate the problem under a deregulated industry.


Distributed generation

With everything interconnected, and open competition occurring in a free market economy, it starts to make sense to allow and even encourage distributed generation (DG). Smaller generators, usually not owned by the utility, can be brought on-line to help supply the need for power. The smaller generation facility might be a home-owner with excess power from their solar panel or wind turbine. It might be a small office with a diesel generator. These resources can be brought on-line either at the utility's behest, or by owner of the generation in an effort to sell electricity. Many small generators are allowed to sell electricity back to the grid for the same price they would pay to buy it. As the 21st century progresses, the electric utility industry seeks to take advantage of novel approaches to meet growing energy demand. Utilities are under pressure to evolve their classic topologies to accommodate distributed generation. As generation becomes more common from rooftop solar and wind generators, the differences between distribution and transmission grids will continue to blur. In July 2017 the CEO of Mercedes-Benz said that the energy industry needs to work better with companies from other industries to form a "total ecosystem", to integrate central and Distributed generation, distributed energy resources (DER) to give customers what they want. The electrical grid was originally constructed so that electricity would flow from power providers to consumers. However, with the introduction of DER, power needs to flow both ways on the electric grid, because customers may have power sources such as solar panels.


Smart grid

The smart grid would be an enhancement of the 20th century electrical grid, using two-way communications and distributed so-called intelligent devices. Two-way flows of electricity and information could improve the delivery network. Research is mainly focused on three systems of a smart grid – the infrastructure system, the management system, and the protection system. The infrastructure system is the energy, information, and communication infrastructure underlying of the smart grid that supports: * Advanced electricity generation, delivery, and consumption * Advanced information metering, monitoring, and management * Advanced communication technologies A smart grid would allow the power industry to observe and control parts of the system at higher resolution in time and space.Alexandra Von Meier (2013). Electrical Engineer 137A: Electric Power Systems. Lecture 2:Introduction to Electric Power Systems, Slide 33. One of the purposes of the smart grid is real time information exchange to make operation as efficient as possible. It would allow management of the grid on all time scales from high-frequency switching devices on a microsecond scale, to wind and solar output variations on a minute scale, to the future effects of the carbon emissions generated by power production on a decade scale. The management system is the subsystem in smart grid that provides advanced management and control services. Most of the existing works aim to improve energy efficiency, demand profile, utility, cost, and emission, based on the infrastructure by using optimization, machine learning, and game theory. Within the advanced infrastructure framework of smart grid, more and more new management services and applications are expected to emerge and eventually revolutionize consumers' daily lives. The protection system of a smart grid provides grid reliability analysis, failure protection, and security and privacy protection services. While the additional communication infrastructure of a smart grid provides additional protective and security mechanisms, it also presents a risk of external attack and internal failures. In a report on cyber security of smart grid technology first produced in 2010, and later updated in 2014, the US National Institute of Standards and Technology pointed out that the ability to collect more data about energy use from customer smart meters also raises major privacy concerns, since the information stored at the meter, which is potentially vulnerable to data breaches, can be mined for personal details about customers. In the U.S., the Energy Policy Act of 2005 and Title XIII of the Energy Independence and Security Act of 2007 are providing funding to encourage smart grid development. The objective is to enable utilities to better predict their needs, and in some cases involve consumers in a time-of-use tariff. Funds have also been allocated to develop more robust energy control technologies.


Grid defection

As there is some resistance in the electric utility sector to the concepts of distributed generation with various renewable energy sources and microscale cogen units, several authors have warned that mass-scale grid defection is possible because consumers can produce electricity using off grid systems primarily made up of solar photovoltaic technology. The Rocky Mountain Institute has proposed that there may be widescale grid defection. This is backed up by studies in the Midwest. However, the paper points out that grid defection may be less likely in countries like Germany which have greater power demands in winter.


See also

* Grid code: a specification for grid-connected equipment * Grid connection * High-voltage transformer fire barriers *
North American Electric Reliability Corporation The North American Electric Reliability Corporation (NERC) is a nonprofit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a ...
(NERC) * Rural Electrification Act


References


External links


Map of U.S. generation and transmission

U.S. electric system is made up of interconnections and balancing authorities
U.S. Energy Information Administration (EIA).
Open Infrastructure Map
is a view of the world's hidden power infrastructure mapped in the OpenStreetMap database. {{Authority control Electrical grid, Electric power distribution Electric power transmission systems la:Cratis electrica no:Fordelingsnett ta:மின் வலைப்பின்னல்