# Electrical grid
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{{Short description|Interconnected network for delivering electricity to consumers}}
{{other uses|Grid (disambiguation)}}
{{Redirect|Power grid|the board game| Power Grid}}
upright=1.7|thumb|Diagram of an electrical grid (generation system in red, transmission system in blue, distribution system in green)
An '''electrical grid''' (or '''electricity network''') is an interconnected network for [electricity delivery](/source/electricity_delivery) from producers to consumers. Electrical grids consist of [power station](/source/power_station)s, [electrical substation](/source/electrical_substation)s to step [voltage](/source/voltage) up or down, [electric power transmission](/source/high_voltage_transmission_line) to carry power over long distances, and finally [electric power distribution](/source/electric_power_distribution) to customers. In that last step, voltage is stepped down again to the required service voltage. Power stations are typically built close to energy sources and far from densely populated areas. Electrical grids vary in size and can cover whole countries or continents. From small to large there are [microgrid](/source/microgrid)s, [wide area synchronous grid](/source/wide_area_synchronous_grid)s, and [super grid](/source/super_grid)s. The combined transmission and distribution network is part of electricity delivery, known as the ''power grid''.
Grids are nearly always synchronous, meaning all distribution areas operate with [three phase](/source/three_phase) [alternating current](/source/alternating_current) (AC) frequencies synchronized (so that voltage swings occur at almost the same time). This allows transmission of AC power throughout the area, connecting the electricity generators with consumers. Grids can enable more efficient [electricity market](/source/electricity_market)s.
Although electrical grids are widespread, {{as of|2016|lc=on}}, 1.4 billion people worldwide were not connected to an electricity grid.[{{cite journal|last= Overland|first= Indra|date= 1 April 2016|title= Energy: The missing link in globalization|url= https://www.researchgate.net/publication/296486356|journal= Energy Research & Social Science|volume= 14|pages= 122–130|doi= 10.1016/j.erss.2016.01.009|url-status= live|archive-url= https://web.archive.org/web/20180205000937/https://www.researchgate.net/publication/296486356|archive-date= 5 February 2018| quote = [...] if all countries in the world were to make do with their own resources, there would be even more energy poverty in the world than there is now. Currently, 1.4 billion people are not connected to an electricity grid [...]|doi-access= free|bibcode= 2016ERSS...14..122O|hdl= 11250/2442076|hdl-access= free}}] As [electrification](/source/electrification) increases, the number of people with access to grid electricity is growing. About 840 million people (mostly in Africa), which is ca. 11% of the World's population, had no access to grid electricity in 2017, down from 1.2 billion in 2010.[{{cite journal | last=Odarno | first=Lily | title=Closing Sub-Saharan Africa's Electricity Access Gap: Why Cities Must Be Part of the Solution | website=World Resources Institute | date=2019-08-14 | url=https://www.wri.org/insights/closing-sub-saharan-africas-electricity-access-gap-why-cities-must-be-part-solution | access-date=2023-12-13}}]
Electrical grids can be prone to malicious intrusion or attack; thus, there is a need for [electric grid security](/source/electric_grid_security). Also as electric grids modernize and introduce computer technology, cyber threats start to become a security risk.[{{cite news|url= https://www.forbes.com/sites/constancedouris/2018/01/16/as-cyber-threats-to-the-electric-grid-rise-utilities-regulators-seek-solutions/#59aa786a343e|title= As Cyber Threats To The Electric Grid Rise, Utilities And Regulators Seek Solutions|last= Douris|first= Constance|work= Forbes|access-date= 27 September 2018|language= en}}] Particular concerns relate to the more complex computer systems needed to manage grids.[
{{cite journal
|last= Overland|first= Indra|date= 1 March 2019
|title= The geopolitics of renewable energy: Debunking four emerging myths
|journal= Energy Research & Social Science|volume= 49
|pages= 36–40|doi= 10.1016/j.erss.2018.10.018
|issn= 2214-6296
|doi-access= free
|bibcode= 2019ERSS...49...36O|hdl= 11250/2579292
|hdl-access= free
}}
]
== Types (grouped by size) ==
{{Power engineering}}
=== Microgrid ===
{{main|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.[{{cite web |title=How Microgrids Work |url=https://www.energy.gov/articles/how-microgrids-work |access-date=19 April 2021 |website=Energy.gov |language=en}}] It might do this in times when the main grid is affected by outages. This is known as [islanding](/source/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.[{{cite web |last1=Khaitan |first1=Siddhartha Kumar |last2=Venkatraman |first2=Ramakrishnan |title=A Survey of Techniques for Designing and Managing Microgrids |url=https://www.academia.edu/23194712 |access-date=19 April 2021 |language=en}}] 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.[{{cite web |date=30 October 2008 |title=EEX Market Monitor Q3/2008 |url=http://www.eex.com/de/document/39600/20081027_EEX_Market_Monitor_Q3_2008_English.pdf |url-status=dead |location=[Leipzig](/source/Leipzig) |publisher=Market Surveillance (HÜSt) group of the [European Energy Exchange](/source/European_Energy_Exchange) |page=4 |archive-url=https://web.archive.org/web/20110710173200/http://www.eex.com/de/document/39600/20081027_EEX_Market_Monitor_Q3_2008_English.pdf |archive-date=10 July 2011 |access-date=6 December 2008}}]
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 line](/source/power_transmission_line)s ([DC tie](/source/DC_tie)s), 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.[{{cite book |last1=Haubrich |first1=Hans-Jürgen |url=http://www.iaew.rwth-aachen.de/cms/upload/PDF/Vorlesungen/Denzel/chapter_0.1.pdf |title=Operation of Interconnected Power Systems |last2=Denzel |first2=Dieter |date=23 October 2008 |publisher=Institute for Electrical Equipment and Power Plants (IAEW) at [RWTH Aachen University](/source/RWTH_Aachen_University) |location=[Aachen](/source/Aachen) |page=3 |chapter=Characteristics of interconnected operation |access-date=6 December 2008 |chapter-url=http://www.iaew.rwth-aachen.de/cms/upload/PDF/Vorlesungen/Denzel/chapter_1.1.pdf |archive-url=https://web.archive.org/web/20110719081241/http://www.iaew.rwth-aachen.de/cms/upload/PDF/Vorlesungen/Denzel/chapter_0.1.pdf |archive-date=19 July 2011 |url-status=dead}} ''(See "Operation of Power Systems" link for title page and table of contents.)'']
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](/source/Kosovo) used more power than it generated due to a dispute with [Serbia](/source/Serbia), leading to the phase across the whole [synchronous grid of Continental Europe](/source/synchronous_grid_of_Continental_Europe) lagging behind what it should have been. The frequency dropped to 49.996 Hz. This caused certain kinds of [clock](/source/clock)s to become six minutes slow.[{{cite news |date=7 March 2018 |title=Serbia, Kosovo power grid row delays European clocks |work=Reuters |url=https://www.reuters.com/article/serbia-kosovo-energy/serbia-kosovo-power-grid-row-delays-european-clocks-idUSL5N1QP2FF}}]
File:European electricity grid.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===
{{main|Super grid}}
[[File:TREC-Map-en.jpg|thumb|right|One conceptual plan of a super grid linking renewable sources across North Africa, the Middle East and Europe ([DESERTEC](/source/DESERTEC))[{{cite journal |last1=Cooper |first1=Christopher |last2=Sovacool |first2=Benjamin K. |date=February 2013 |title=Miracle or mirage? The promise and peril of desert energy part 1. |url= |journal=Renewable Energy |volume=50 |issue= |pages=628–636 |doi=10.1016/j.renene.2012.07.027 |bibcode=2013REne...50..628C |access-date=}}]]]
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](/source/energy_transition) by smoothing local fluctuations of [wind energy](/source/wind_energy) and [solar energy](/source/solar_energy). In this context, they are considered as a key technology to [mitigate](/source/Climate_change_mitigation) [global warming](/source/global_warming). Super grids typically use [high-voltage direct current](/source/high-voltage_direct_current) (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.[{{cite web |title=UHV Grid |url=https://en.geidco.org/aboutgei/uhv/ |url-status=dead |archive-url=https://web.archive.org/web/20200201182520/https://en.geidco.org/aboutgei/uhv/ |archive-date=1 February 2020 |access-date=26 January 2020 |publisher=Global Energy Interconnection (GEIDCO)}}]
Electric utilities between regions are many times interconnected for improved economy and reliability. [Electrical interconnector](/source/Electrical_interconnector)s 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.[. (2001). Glover J. D., Sarma M. S., Overbye T. J. (2010) Power System and Analysis 5th Edition. Cengage Learning. Pg 10.]
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.[{{Cite journal |last1=Mezősi |first1=András |last2=Pató |first2=Zsuzsanna |last3=Szabó |first3=László |year=2016 |title=Assessment of the EU 10% interconnection target in the context of CO2 mitigation† |journal=Climate Policy |volume=16 |issue=5 |pages=658–672 |doi=10.1080/14693062.2016.1160864 |doi-access=free|bibcode=2016CliPo..16..658M }}]
==Components==
===Generation===
{{main|Electricity generation}}
[[File:Turbogenerator01.jpg|thumb|upright=1.3|[Turbo generator](/source/Turbo_generator)]]
Electricity generation is the process of generating [electric power](/source/electric_power) at [power station](/source/power_station)s. This is done ultimately from sources of [primary energy](/source/primary_energy) typically with [electromechanical](/source/electromechanical) [generators](/source/electric_generator) driven by [heat engine](/source/heat_engine)s from [fossil](/source/fossil_fuel), [nuclear](/source/nuclear_power), and [geothermal](/source/geothermal_power) sources, or driven by the [kinetic energy](/source/kinetic_energy) of water or wind. Other power sources are [photovoltaics](/source/photovoltaics) driven by solar insolation, and [grid batteries](/source/grid_battery).{{refn|group=nb|Note that grid batteries are a useful source of power for grids, but not of primary energy and so they must be charged by another source of energy prior to use.}}
The sum of the power outputs of generators on the grid is the production of the grid, typically measured in [gigawatts](/source/gigawatts) (GW).
===Transmission===
{{main|Electric power transmission}}
[[File:500kV 3-Phase Transmission Lines.png|thumb|500 kV [three-phase electric power](/source/three-phase_electric_power) Transmission Lines at [Grand Coulee Dam](/source/Grand_Coulee_Dam); four circuits are shown; two additional circuits are obscured by trees on the right; the entire 7079 MW generation capacity of the dam is accommodated by these six circuits.]]thumb|Network diagram of a high voltage transmission system, showing the interconnection between the different voltage levels. This diagram depicts the electrical structure[{{cite journal |last1=Cuffe |first1=Paul |last2=Keane |first2=Andrew |year=2017 |title=Visualizing the Electrical Structure of Power Systems |journal=IEEE Systems Journal |volume=11 |issue=3 |pages=1810–1821 |bibcode=2017ISysJ..11.1810C |doi=10.1109/JSYST.2015.2427994 |issn=1932-8184 |s2cid=10085130 |hdl-access=free |hdl=10197/7108}}] of the network, rather than its physical geography.Electric power transmission is the bulk movement of [electrical energy](/source/electrical_energy) from a generating site, via a web of interconnected lines, to an [electrical substation](/source/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. Transmission networks are built with redundant pathways to prevent a [single point of failure](/source/single_point_of_failure). In case of line failures this [redundancy](/source/Redundancy_(engineering)) allows power to be simply rerouted while repairs are done.
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 currents. Therefore, voltages are stepped up at the generating station, and stepped down at local substations for distribution to customers.
Most transmission is [three-phase](/source/Three-phase_electric_power). 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.[{{Cite web|last=Sajip|first=Jahnavi|title=Why Do We Use Three-Phase Power?|url=https://www.ny-engineers.com/blog/why-do-we-use-three-phase-power|access-date=22 April 2021|website=www.ny-engineers.com|language=en}}] 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.[{{cite web |url=https://www.aep.com/about/transmission/docs/transmission-facts.pdf |title=Transmission Facts |website=www.aep.com |access-date=11 January 2022 |archive-url=https://web.archive.org/web/20110604181007/https://www.aep.com/about/transmission/docs/transmission-facts.pdf |archive-date=4 June 2011 |url-status=dead}}] However, [high-voltage direct current](/source/high-voltage_direct_current) 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.
===Substations===
{{main|Electrical substation}}
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.[{{cite news |title=The basic things about substations you MUST know in the middle of the night! |url=https://electrical-engineering-portal.com/substation-basics |website=EEP – Electrical Engineering Portal |access-date=23 April 2021 |language=en |date=9 January 2019}}]
The three main types of substations, by function, are:[{{cite web |title=Electrical substation |url=https://energyeducation.ca/encyclopedia/Electrical_substation |website=energyeducation.ca |publisher=University of Calgary |access-date=23 April 2021 |language=en}}]
* Step-up substation: these use [transformer](/source/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](/source/Circuit_breaker)s: used to automatically break a circuit and isolate a fault in the system.[{{cite book |last1=Hayes |first1=Brian |title=Infrastructure : a field guide to the industrial landscape |date=2005 |publisher=W.W. Norton |location=New York |isbn=0-393-05997-9 |edition=1st}}]
* [Switch](/source/Switch)es: to control the flow of electricity, and isolate equipment.[{{cite news |last1=Hillhouse |first1=Grady |title=How Do Substations Work? |url=https://practical.engineering/blog/2019/8/26/how-do-substations-work |website=Practical Engineering |access-date=23 April 2021}}]
* The substation [busbar](/source/busbar): typically a set of three conductors, one for each phase of current. The substation is organized around the buses, and they are connected to incoming lines, transformers, protection equipment, switches, and the outgoing lines.[{{cite web | url=https://www.eon.se/om-e-on/verksamhetsomraden/elnaet | title=Om E.ON {{!}} Elnät }}] Primary distribution lines carry this medium voltage power to [distribution transformer](/source/distribution_transformer)s located near the customer's premises. Distribution transformers again lower the voltage to the [utilization voltage](/source/utilization_voltage). Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the [subtransmission](/source/subtransmission) level.[{{Cite news|url=http://science.howstuffworks.com/environmental/energy/power5.htm|title=How Power Grids Work|website=HowStuffWorks|date=April 2000|access-date=18 March 2016}}]
Distribution networks are divided into two types, radial or network.[{{cite book|first1=Abdelhay A.|last1=Sallam|title=Electric Distribution Systems|first2=Om P.|last2=Malik|date=May 2011|publisher=IEEE Computer Society Press|isbn=9780470276822|page=21|name-list-style=amp}}]
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](/source/busbar) 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===
{{main|Grid energy storage}}
thumb|Energy from fossil or nuclear power plants and renewable sources is stored for use by customers.
thumb|Simplified grid energy flow over the course of a day
''Grid energy storage'' (also called ''large-scale energy storage'') is a collection of methods used for [energy storage](/source/energy_storage) on a large scale within an [electrical power grid](/source/grid_(electricity)). Electrical energy is stored during times when electricity is plentiful and inexpensive (especially from [intermittent power](/source/Variable_renewable_energy) sources such as [renewable electricity](/source/renewable_electricity) from [wind power](/source/wind_power), [tidal power](/source/tidal_power) and [solar power](/source/solar_power)) or when demand is low, and later power is generated when demand is high, and electricity prices tend to be higher.
{{As of|2020}}, the largest form of grid energy storage is dammed [hydroelectricity](/source/hydroelectricity), with both conventional hydroelectric generation as well as [pumped storage hydroelectricity](/source/Pumped-storage_hydroelectricity).
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](/source/peaking_power_plant)s to fill in supply gaps and [demand response](/source/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](/source/Baseload) is the minimum load on the grid over any given period, [peak demand](/source/peak_demand) 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 plant](/source/peaking_plant)s that are generators optimised to come on-line quickly but these too are becoming less common.{{Clarify|reason=Both of these things are said to be becoming less common, but *what* exactly are they being replaced with?|date=February 2025}}
However, if the demand of electricity exceeds the capacity of a local power grid, it will cause safety issues like burning out.[{{Cite journal |last1=Wang |first1=Yingcheng |last2=Gladwin |first2=Daniel |date=January 2021 |title=Power Management Analysis of a Photovoltaic and Battery Energy Storage-Based Smart Electrical Car Park Providing Ancillary Grid Services |journal=Energies |language=en |volume=14 |issue=24 |pages=8433 |doi=10.3390/en14248433 |issn=1996-1073|doi-access=free }}]
===Voltage ===
Grids are designed to supply electricity to their customers at largely constant voltages. This has to be achieved with varying demand, variable [reactive](/source/reactive_power) loads, and even nonlinear loads, with electricity provided by generators and distribution and transmission equipment that are not perfectly reliable.[{{cite web|title=Chapter 2: Power System Voltage Stability and Models of Devices|url=https://www.springer.com/cda/content/document/cda_downloaddocument/9789812871152-c2.pdf?SGWID=0-0-45-1466523-p176786301|url-status=live|archive-url=https://web.archive.org/web/20180508085728/https://www.springer.com/cda/content/document/cda_downloaddocument/9789812871152-c2.pdf?SGWID=0-0-45-1466523-p176786301|archive-date=8 May 2018|access-date=28 August 2017}}] Often grids use [tap changer](/source/tap_changer)s on transformers near to the consumers to adjust the voltage and keep it within specification.
===Frequency===
{{main|Utility 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](/source/Governor_(device)) 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](/source/Automatic_generation_control) (AGC) 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 control](/source/droop_speed_control)). 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](/source/Electric_clock) from gaining or losing significant time over the course of a whole 24 hour period.
Neighbouring grids that are not directly connected are almost always out-of-phase with each other. Instead, [high-voltage direct current](/source/high-voltage_direct_current) lines or [variable-frequency transformer](/source/variable-frequency_transformer)s are used, which allow two out-of-phase synchronous grids to share power.
===Capacity and firm capacity===
The sum of the maximum power outputs ([nameplate capacity](/source/nameplate_capacity)) 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](/source/spinning_reserve)) 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](/source/merit_order) according to their [marginal cost](/source/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.
== Management, operation and ownership ==
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](/source/North_American_Electric_Reliability_Corporation) 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](/source/National_Interest_Electric_Transmission_Corridor)s, where it believes transmission bottlenecks have developed.
Where multiple utilities own generators connected to one electrical grid [power pool](/source/power_pool)s are often formed which have agreements about responsibilities.
Each grid may have a system operator that is responsible for day-to-day running of one or more grids.
== Failures and issues ==
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](/source/cascading_failure) and widespread [power outage](/source/power_outage).
=== Brownout ===
{{main|Brownout (electricity)}}
[[File:20110313-TokyoTower.jpg|thumb|upright|A brownout near [Tokyo Tower](/source/Tokyo_Tower) in [Tokyo](/source/Tokyo), Japan]]
A ''brownout'' is an intentional or unintentional drop in voltage in an electrical [power supply](/source/power_supply) system. Intentional brownouts are used for load reduction in an emergency.[Steven Warren Blume ''Electric power system basics: for the nonelectrical professional''. John Wiley & Sons, 2007 {{ISBN|0470129875}} p. 199] The reduction lasts for minutes or hours, as opposed to short-term [voltage sag](/source/voltage_sag) (or dip). The term brownout comes from the dimming experienced by incandescent lighting when the voltage sags. A [voltage reduction](/source/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](/source/power_outage), known as a [blackout](/source/Power_outage).[Alan Wyatt, ''Electric Power Challenges and Choices'', The Book Press Limited, Toronto, 1986 {{ISBN|0-920650-00-7}} page 63]
=== Blackout ===
{{main|Power outage}}
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, [substations](/source/Electrical_substation) or other parts of the [distribution](/source/electricity_distribution) system, a [short circuit](/source/short_circuit), [cascading failure](/source/Cascading_failure), [fuse](/source/fuse_(electrical)) or [circuit breaker](/source/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 [hospital](/source/hospital)s, [sewage treatment](/source/sewage_treatment) plants, [mines](/source/mining), shelters and the like will usually have backup power sources such as [standby generators](/source/emergency_power_system), which will automatically start up when electrical power is lost. Other critical systems, such as [telecommunication](/source/telecommunication), are also required to have emergency power. The [battery room](/source/battery_room) of a telephone exchange usually has arrays of [lead–acid batteries](/source/Lead%E2%80%93acid_battery) for backup and also a socket for connecting a generator during extended periods of outage.
=== Load shedding ===
{{main|Demand response}}
[Electrical generation](/source/Electrical_generation) and transmission systems may not always meet peak demand requirements— the greatest amount of [electricity](/source/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](/source/brownout_(electricity))s), 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 blackout](/source/rolling_blackout)s or by agreements with specific high-use industrial consumers to turn off equipment at times of system-wide peak demand.
=== Black start ===
{{main|Black start}}
[[File:Toronto ON 2003 Blackout.jpg|thumb|right|alt=City skyline at dusk with only a very few office building windows lit|Toronto during the [Northeast blackout of 2003](/source/Northeast_blackout_of_2003), which required black-starting of generating stations]]
A ''black start'' is the process of restoring an electric power station or a part of an [electric grid](/source/electric_grid) to operation without relying on the external [electric power transmission network](/source/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 {{ISBN|978-0-471-49016-6}} 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 [bootstrap](/source/Bootstrapping) the power grid into operation.
To provide a black start, some power stations have small [diesel generator](/source/diesel_generator)s, normally called the ''black start diesel generator'' (BSDG), which can be used to start larger generators (of several [megawatt](/source/megawatt)s 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 pump](/source/boiler_feedwater_pump)s, 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](/source/excitation_(magnetic)) 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](/source/combustion_turbine) can be configured for black start, providing another option in places without suitable hydroelectric plants.[Philip P. Walsh, Paul Fletcher ''Gas turbine performance'', John Wiley and Sons, 2004 {{ISBN|0-632-06434-X}}, page 486] 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.[{{Cite web | url=https://www.energy-storage.news/news/california-batterys-black-start-capability-hailed-as-major-accomplishment-i | title=California battery's black start capability hailed as 'major accomplishment in the energy industry'| date=17 May 2017}}]
===Obsolescence===
Despite novel institutional arrangements and network designs, power delivery infrastructures is experiencing aging across the developed world. Contributing factors include:
* Aging equipment – older equipment has higher [failure rate](/source/failure_rate)s, leading to customer interruption rates affecting the economy and society; also, older assets and facilities lead to higher inspection [maintenance](/source/Maintenance%2C_repair%2C_and_operations) costs and further [repair](/source/Maintenance%2C_repair%2C_and_operations) and [restoration](/source/Renovation) costs.
* Obsolete system layout – older areas require serious additional substation sites and [rights-of-way](/source/Right-of-way_(transportation)) that cannot be obtained in the current area and are forced to use existing, insufficient facilities.
* Outdated engineering – traditional tools for [power delivery](/source/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](/source/planning), [engineering](/source/engineering), operating of system using concepts and procedures that worked in vertically integrated industry exacerbate the problem under a deregulated industry.[Willis, H. L., Welch, G. V., and Schrieber, R. R. (2001). ''Aging Power Delivery Infrastructures''. New York: Marcel Dekker, Inc. 551 pgs.]
==Trends==
===Demand response===
[Demand response](/source/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.[{{cite news
|url = https://www.reuters.com/article/pressRelease/idUS206497+16-May-2008+PRN20080516
|title = Industry Cross-Section Develops Action Plans at PJM Demand Response Symposium
|work = [Reuters](/source/Reuters)
|date = 13 August 2008
|access-date = 22 November 2008
|quote = Demand response can be achieved at the wholesale level with major energy users such as industrial plants curtailing power use and receiving payment for participating.
|url-status = dead
|archive-url = https://web.archive.org/web/20090219130523/http://www.reuters.com/article/pressRelease/idUS206497+16-May-2008+PRN20080516
|archive-date = 19 February 2009
}}] Technologies such as smart metering can encourage customers to use power when electricity is plentiful by allowing for variable pricing.
===Smart grid===
{{excerpt|smart grid}}
===Grid defection===
Resistance to distributed generation among grid operators may encourage providers to leave the grid and instead distribute power to smaller geographies.[{{cite journal | last1 = Kantamneni | first1 = Abhilash | last2 = Winkler | first2 = Richelle | last3 = Gauchia | first3 = Lucia | last4 = Pearce | first4 = Joshua M. | year = 2016| title = free open access Emerging economic viability of grid defection in a northern climate using solar hybrid systems | url = https://www.academia.edu/25363058 | journal = Energy Policy | volume = 95 | pages = 378–389 | doi = 10.1016/j.enpol.2016.05.013 }}][{{cite journal | last1 = Khalilpour | first1 = R. | last2 = Vassallo | first2 = A. | year = 2015 | title = Leaving the grid: An ambition or a real choice? | journal = Energy Policy | volume = 82 | pages = 207–221 | doi = 10.1016/j.enpol.2015.03.005 | bibcode = 2015EnPol..82..207K }}][{{cite journal | last1 = Kumagai | first1 = J | year = 2014 | title = The rise of the personal power plant | journal = IEEE Spectrum | volume = 51 | issue = 6| pages = 54–59 | doi = 10.1109/mspec.2014.6821622 | s2cid = 36554641 }}]
The [Rocky Mountain Institute](/source/Rocky_Mountain_Institute)[The Economics of Grid Defection - Rocky Mountain Institute {{cite web |title=The Economics of Grid Defection |url=http://www.rmi.org/electricity_grid_defection |url-status=dead |archive-url=https://web.archive.org/web/20160812215342/http://www.rmi.org/electricity_grid_defection |archive-date=12 August 2016 |access-date=13 August 2016}}] and other studies[Andy Balaskovitz [http://midwestenergynews.com/2016/06/14/net-metering-changes-could-drive-people-off-grid-michigan-researchers-say/ Net metering changes could drive people off grid, Michigan researchers say] {{webarchive|url=https://web.archive.org/web/20160615112536/http://midwestenergynews.com/2016/06/14/net-metering-changes-could-drive-people-off-grid-michigan-researchers-say/|date=15 June 2016}} – MidWest Energy News] foresee widescale grid defection. However, grid defection may be less likely in places such as Germany that have greater power demands in the winter.[{{Cite web | url=https://energytransition.org/2015/06/grid-defection/ | title=Grid defection and why we don't want it| date=16 June 2015}}]
==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](/source/coal_gas). Coal gas was first produced on customer's premises but later evolved into [gasification](/source/gasification) plants that enjoyed [economies of scale](/source/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](/source/hydrogen) and [carbon monoxide](/source/carbon_monoxide). They also posed a fire hazard. In the 1880s electric lighting soon became advantageous compared to gas lighting.
[Electric utility](/source/Electric_utility) companies established [central stations](/source/Central_station_(electricity)) 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](/source/war_of_the_currents) was settled in favor of [AC power](/source/AC_power), 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](/source/Electricity_liberalization) the regulation of the [electricity market](/source/electricity_market) in ways that have led to the separation of the electricity transmission business from the distribution business.[{{cite web | last=Warwick | first=W.M. |title=A Primer on Electric Utilities, Deregulation, and Restructuring of U.S. Electricity Markets | url=https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-13906.pdf | date=May 2002 |publisher=[United States Department of Energy](/source/United_States_Department_of_Energy) [Federal Energy Management Program](/source/Federal_Energy_Management_Program) (FEMP) |access-date=2023-12-13}}]
In the United Kingdom, [Charles Merz](/source/Charles_Merz), of the [Merz & McLellan](/source/Merz_%26_McLellan) consulting partnership, built the [Neptune Bank Power Station](/source/Neptune_Bank_Power_Station) near [Newcastle upon Tyne](/source/Newcastle_upon_Tyne) in 1901,[{{cite web |author=Mr Alan Shaw |date=29 September 2005 |title=Kelvin to Weir, and on to GB SYS 2005 |url=http://www.royalsoced.org.uk/enquiries/energy/evidence/ShawA1.pdf |url-status=live |archive-url=https://web.archive.org/web/20090304090015/http://www.royalsoced.org.uk/enquiries/energy/evidence/ShawA1.pdf |archive-date=4 March 2009 |publisher=Royal Society of Edinburgh}}] and by 1912 had developed into the largest integrated power system in Europe.[{{cite web |title=Survey of Belford 1995 |url=http://www.nnouk.com/survey/survey-utilities.shtml |url-status=dead |archive-url=https://web.archive.org/web/20160412000737/http://www.nnouk.com/survey/survey-utilities.shtml |archive-date=2016-04-12 |access-date=2013-10-06 |publisher=North Northumberland Online}}] 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) Act 1919](/source/Electricity_(Supply)_Act_1919). The bill was the first step towards an integrated electricity system. In 1925 the [Weir](/source/William_Weir%2C_1st_Viscount_Weir) Committee recommended the creation of a "national gridiron" and so the [Electricity (Supply) Act 1926](/source/Electricity_(Supply)_Act_1926) created the [Central Electricity Board](/source/Central_Electricity_Board) (CEB).[{{cite web |title=Lighting by electricity |url=http://www.nationaltrust.org.uk/main/w-chl/w-places_collections/w-collections-main/w-collections-highlights/w-collections-lighting-electricity.html |url-status=dead |archive-url=https://web.archive.org/web/20110629091025/http://www.nationaltrust.org.uk/main/w-chl/w-places_collections/w-collections-main/w-collections-highlights/w-collections-lighting-electricity.html |archive-date=29 June 2011 |publisher=[The National Trust](/source/National_Trust_for_Places_of_Historic_Interest_or_Natural_Beauty)}}] The CEB standardized the nation's electricity supply and established the first synchronized AC grid, running at 132 kilovolts and 50 [hertz](/source/hertz) but initially operated as regional grids. After brief overnight interconnection in 1937 they permanently and officially joined in 1938 becoming the [UK National Grid](/source/National_Grid_(UK)).
In France, [electrification](/source/electrification) began in the 1900s, with 700 [communes](/source/Communes_of_France) 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](/source/%C3%89lectricit%C3%A9_de_France). 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. Starting on May 29, 1986, the end user service voltage will progressively change to 230/400 V ±10%.[Philippe CARRIVE, Réseaux de distribution – Structure et planification, volume D4210, collection Techniques de l'ingénieur, page 6.][{{cite web|language=fr|title=Journal Officiel n°0146, page 7895|url=https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000000320337/|date=25 June 1986}}]
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](/source/Public_Utility_Holding_Company_Act) (U.S.), electric utilities were recognized as [public good](/source/Public_good_(economics))s of importance and were given outlined restrictions and regulatory oversight of their operations. The [Energy Policy Act of 1992](/source/Energy_Policy_Act_of_1992) required transmission line owners to allow electric generation companies open access to their network[Mazer, 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.[{{cite book |url=https://books.google.com/books?id=zd5WAAAAMAAJ |title=People's Republic of China Year Book |publisher=Xinhua Publishing House |year=1989 |pages=190}}] In August 1961, the electrification of the Baoji-Fengzhou section of the [Baocheng Railway](/source/Baocheng_Railway) was completed and delivered for operation, becoming China's first [electrified railway](/source/electrified_railway).[{{cite book |url=https://books.google.com/books?id=6mxpHRU2wv4C |title=China Report: Economic affairs |publisher=Foreign Broadcast Information Service, Joint Publications Research Service |year=1984 |pages=54}}] From 1958 to 1998, China's electrified railway reached {{convert|6,200|mi|km|abbr=off}}.[{{Cite web |date=3 October 2018 |title=Hong Kong Express Rail Link officially opens |url=http://www.xinhuanet.com/2018-10/03/c_129965424.htm |url-status=dead |archive-url=https://web.archive.org/web/20181018025615/http://www.xinhuanet.com/2018-10/03/c_129965424.htm |archive-date=18 October 2018 |website=[Xinhuanet.com](/source/Xinhuanet.com)}}] As of the end of 2017, this number has reached {{convert|54,000|mi|km|abbr=off}}.[{{Cite web |author=Avishek G Dastidar |date=13 September 2018 |title=After initial questions, government clears 100% Railways electrification |url=https://indianexpress.com/article/india/indian-railways-electrification-piyush-goyal-5353537/ |website=[The Indian Express](/source/The_Indian_Express)}}] In the current [railway electrification system](/source/railway_electrification_system) of China, [https://g.esgcc.com.cn/ State Grid Corporation of China]—{{Webarchive|url=https://web.archive.org/web/20211221190902/https://g.esgcc.com.cn/ |date=2021-12-21 }}—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](/source/Jingtong_Railway), [Haoji Railway](/source/Haoji_Railway), [Zhengzhou–Wanzhou high-speed railway](/source/Zhengzhou%E2%80%93Wanzhou_high-speed_railway), et cetera, providing power supply guarantee for 110 traction stations, and its cumulative power line construction length reached 6,586 kilometres.[{{Cite web |date=6 January 2020 |title=Beijing–Zhangjiakou intercity railway opens |url=http://dsm.ndrc.gov.cn/dsm_portalweb/rest/siteChannels/4724.html |url-status=dead |archive-url=https://web.archive.org/web/20210303113726/http://dsm.ndrc.gov.cn/dsm_portalweb/rest/siteChannels/4724.html |archive-date=3 March 2021 |access-date=24 June 2020 |website=[National Development and Reform Commission](/source/National_Development_and_Reform_Commission)}}]
==See also==
* [Dispatchable generation](/source/Dispatchable_generation)
* [Grid code](/source/Grid_code): a specification for grid-connected equipment
* [Inertial response](/source/Inertial_response)
* [North American power transmission grid](/source/North_American_power_transmission_grid)
* [Sustainable energy](/source/Sustainable_energy)
==Notes==
{{reflist|group=nb}}
==References==
{{Reflist}}
==External links==
{{commons category|Power grids}}
* [https://openinframap.org Open Infrastructure Map] is a view of the world's hidden power infrastructure mapped in the [OpenStreetMap](/source/OpenStreetMap) database.
{{Electricity generation|state=expanded}}
{{Electricity grid modernization}}
{{Authority control}}
Category:Electrical grid
Category:Electric power distribution
Category:Electric power transmission systems
[ta:மின் வலைப்பின்னல்](/source/ta%3A%E0%AE%AE%E0%AE%BF%E0%AE%A9%E0%AF%8D_%E0%AE%B5%E0%AE%B2%E0%AF%88%E0%AE%AA%E0%AF%8D%E0%AE%AA%E0%AE%BF%E0%AE%A9%E0%AF%8D%E0%AE%A9%E0%AE%B2%E0%AF%8D)
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Adapted from the Wikipedia article [Electrical grid](https://en.wikipedia.org/wiki/Electrical_grid) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Electrical_grid?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.