View source for National Grid (Great Britain)

{{Short description|High-voltage electric power transmission network in Great Britain}}
{{about|the power grid in Great Britain|the UK Ordnance Survey National Grid for mapping co-ordinates in Great Britain|Ordnance Survey National Grid|the company|National Grid plc}}
[[File:Map of the National Grid in Great Britain.svg|thumb|Map of the National Grid]]
The '''National Grid''' is the high-voltage [[electric power transmission]] [[Grid (electricity)|network]] supporting the [[Electricity in Great Britain|UK's electricity market]], connecting [[power station]]s and major [[Electrical substation|substations]], and ensuring that electricity generated anywhere on the grid can be used to satisfy demand elsewhere. The network serves the majority of Great Britain and some of the surrounding islands. It does not cover [[Northern Ireland]], which is part of the [[Electricity sector in Ireland|Irish single electricity market]].
The National Grid is a [[wide area synchronous grid]] operating at a nominal 50 hertz. Most of the physical HV parts of the grid consists of 400 kV lines as well as some 275 kV lines that collectively form a [[supergrid]]. It has several [[undersea power cable|undersea interconnectors]]: an AC connector to the [[Isle of Man]], and DC connectors to Northern Ireland, the [[Shetland Islands]], the Republic of Ireland, France, Belgium, the Netherlands, Norway, and Denmark.
Since the privatisation of the [[Central Electricity Generating Board]] in 1990, the National Grid in England and Wales is owned by [[National Grid plc]]. In Scotland the grid is owned by [[ScottishPower|ScottishPower Transmission]] in the south, and by [[SSE plc|SSE]] in the north. Infrastructure connecting offshore wind farms to the grid is owned by [[Offshore transmission owner|offshore transmission owners]]. National Grid plc is the [[transmission system operator]] for the whole GB grid.<ref name=":0">{{Cite web|url=https://www.ofgem.gov.uk/electricity/transmission-networks/gb-electricity-transmission-network|title=The GB electricity transmission network|website=Ofgem|language=en-gb|access-date=25 June 2018}}</ref>
==History==
{{more citations needed section|date=February 2019}}
[[File:Electricity Pylon - Chatsworth Crescent - geograph.org.uk - 488767.jpg|thumb|upright|Electricity pylons in a suburban area of [[Pudsey]], West Yorkshire]]
At the end of the 19th century, [[Nikola Tesla]] established the principles of [[Three-phase electric power|three-phase]] high-voltage [[electric power distribution]] while he was working for [[Westinghouse Electric (1886)|Westinghouse]] in the United States.<ref>{{Cite web |last= |first= |date=2022-03-30 |title=Nikola Tesla: Father of Our Modern Energy Systems |url=https://justenergy.com/blog/nikola-tesla/ |access-date=2023-01-29 |website=Just Energy |language=en-US}}</ref><ref>{{Cite web |last=Massachusetts Institute of Technology |title=NIKOLA TESLA |url=https://web.mit.edu/most/Public/Tesla1/etradict2.htm |access-date=2023-01-29 |website=web.mit.edu}}</ref> The first use of this system in the United Kingdom was by [[Charles Merz]], of the [[Merz & McLellan]] consulting partnership, at his [[Neptune Bank Power Station]] near [[Newcastle upon Tyne]]. This opened in 1901,<ref>{{cite web
|url=http://www.royalsoced.org.uk/enquiries/energy/evidence/ShawA1.pdf
|title=Kelvin to Weir, and on to GB SYS 2005
|date=29 September 2005
|author=Alan Shaw
|publisher=Royal Society of Edinburgh
|access-date=12 November 2006
|archive-url=https://web.archive.org/web/20090304090015/http://www.royalsoced.org.uk/enquiries/energy/evidence/ShawA1.pdf
|archive-date=4 March 2009
|url-status=dead
}}</ref> and by 1912 had developed into the largest integrated power system in Europe.<ref>{{cite web |url=http://www.nnouk.com/survey/survey-utilities.shtml |title=Survey of Belford 1995 |publisher=North Northumberland Online |access-date=6 February 2007 |archive-date=12 April 2016 |archive-url=https://web.archive.org/web/20160412000737/http://www.nnouk.com/survey/survey-utilities.shtml |url-status=dead }}</ref> The rest of the country, however, continued to use a patchwork of small supply networks.
In 1925, the British government asked [[William Douglas Weir|Lord Weir]], a [[Glasgow|Glaswegian]] industrialist, to solve the problem of Britain's inefficient and fragmented electricity supply industry. Weir consulted Merz, and the result was the [[Electricity (Supply) Act 1926]], which recommended that a "national [[electrical grid|gridiron]]" supply system be created.<ref>{{cite web |url=http://www.nationaltrust.org.uk/main/w-chl/w-places_collections/w-collections-main/w-collections-highlights/w-collections-lighting-electricity.html |title=Lighting by electricity |publisher=[[National Trust for Places of Historic Interest or Natural Beauty|The National Trust]] |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 |df=dmy-all }}</ref> The 1926 Act created the [[Central Electricity Board]], which set up the UK's first synchronised, nationwide AC grid, running at 132&nbsp;kV, 50&nbsp;Hz.<ref>{{Cite web |title=Electricity Act 1926 {{!}} Electricity System {{!}} IESIS Energy |url=http://www.iesisenergy.org/electricityact.html#:~:text=The%20Government%20pushed%20through%20the,by%20the%20end%20of%201935. |access-date=2024-07-31 |website=www.iesisenergy.org}}</ref>
[[File:National Grid helicopter.jpg|thumb|upright|National Grid helicopter inspecting overhead cables in [[Greater Manchester]]]]
The grid was created with {{convert|4000|mile|km|order=flip}} of cables – mostly [[Overhead power line|overhead]] – linking the 122 most efficient power stations. The first "grid tower" was erected near Edinburgh on 14 July 1928,<ref>{{Cite book|title=Electricity supply in the United Kingdom : a chronology – from the beginnings of the industry to 31 December 1985|date=1987|publisher=The Electricity Council|isbn=085188105X|oclc=17343802}}</ref> and work was completed in September 1933, ahead of schedule and on budget.<ref>The Secret Life of the National Grid: Wiring the Nation</ref><ref name=indigilb>{{cite news|url=https://www.independent.co.uk/arts-entertainment/tv/features/power-struggle-the-national-grid-was-created-to-provide-energy-for-all-but-thats-when-the-problems-2113229.html |archive-url=https://ghostarchive.org/archive/20220618/https://www.independent.co.uk/arts-entertainment/tv/features/power-struggle-the-national-grid-was-created-to-provide-energy-for-all-but-thats-when-the-problems-2113229.html |archive-date=18 June 2022 |url-access=subscription |url-status=live |title=Power struggle: The National Grid was created to provide energy for all – but that's when the problems really began|author=Gerard Gilbert |newspaper=[[The Independent]] |date=22 October 2010 |access-date=2016-08-21}}</ref> It began operating in 1933 as a series of regional grids with auxiliary interconnections for emergency use. Following the unauthorised but successful short term parallelling of all regional grids by the night-time engineers on 29 October 1937,<ref name="cochrane">{{cite book |last= Cochrane|first= Rob|date= 1985|title= Power to the People|publisher= Newnes|isbn=0600358755}}</ref> by 1938 the grid was operating as a national system. The growth by then in the number of electricity users was the fastest in the world, rising from three quarters of a million in 1920 to nine million in 1938.<ref name=indigilb/> The grid proved its worth during the [[The Blitz|Blitz]], when South Wales provided power to replace lost output from [[Battersea power station|Battersea]] and [[Fulham Power Station|Fulham]] power stations.<ref name=indigilb/> The grid was nationalised by the [[Electricity Act 1947]], which also created the [[British Electricity Authority]]. In 1949, the British Electricity Authority decided to upgrade the grid by adding 275&nbsp;kV links.
At its inception in 1950, the 275&nbsp;kV Transmission System was designed to form part of a national supply system with an anticipated total demand of 30,000&nbsp;MW by 1970. The predicted demand was already exceeded by 1960. This rapid growth led the [[Central Electricity Generating Board]] (created in 1958) to carry out a study in 1960 of future transmission needs.<ref name="booth">{{Cite journal| doi = 10.1049/pi-a.1962.0143| issn = 0369-8882| volume = 109| issue = 48| pages = 493| last1 = Booth| first1 = E.S.| last2 = Clark| first2 = D.| last3 = Egginton| first3 = J.L.| last4 = Forrest| first4 = J.S.| title = The 400 kV grid system for England and Wales| journal = Proceedings of the IEE - Part A: Power Engineering | accessdate = 2023-02-04| date = 1962| url = https://digital-library.theiet.org/content/journals/10.1049/pi-a.1962.0143}}</ref>
Considered in the study, together with the increased demand, was the effect on the transmission system of the rapid advances in generator design resulting in projected power stations of 2,000–3,000&nbsp;MW installed capacity. These new stations were mostly to be sited where advantage could be taken of a surplus of cheap low-grade fuel and adequate supplies of cooling water, but these sites did not coincide with the load centres. [[West Burton power stations|West Burton]]'s 4&nbsp;× 500&nbsp;MW machines, in the [[Nottinghamshire]] coalfield near the [[River Trent]], is an example. These developments shifted the emphasis on the transmission system from interconnection to bulk power transfers from the generation areas to the load centres, such as the anticipated transfer in 1970 of some 6,000&nbsp;MW from the [[Midlands]] to the [[home counties]].<ref name="booth"/>
Continued reinforcement and extension of the 275&nbsp;kV systems was examined as a possible solution. However, in addition to the technical problem of high fault levels, many more lines would have been required to obtain the estimated transfers at 275&nbsp;kV. As this was not consistent with the Central Electricity Generating Board's policy of preservation of amenities, a better solution was sought. Consideration was given to 400&nbsp;kV and 500&nbsp;kV schemes: both gave a sufficient margin for future expansion. The decision in favour of a 400&nbsp;kV system was made for two main reasons. Firstly the majority of the 275&nbsp;kV lines could be uprated to 400&nbsp;kV, and secondly it was envisaged that operation at 400&nbsp;kV could begin in 1965 compared with 1968 for a 500&nbsp;kV scheme.<ref name="booth"/> Design work was started and in order to meet the programme for 1965 it was necessary for the contract engineering for the first projects to run concurrently with the design. One of these projects was the West Burton 400&nbsp;kV Indoor Substation, the first section of which was commissioned in June 1965. From 1965, the grid was partly upgraded to 400&nbsp;kV, beginning with a {{convert|150|mi|km|adj=on}} line from [[Sundon]] to [[West Burton power stations|West Burton]], to become the [[super grid|Supergrid]].
In the 2010 issue of the code that governs the National Grid, the ''[[Grid Code]]'',<ref>{{cite web
|url          = http://www.nationalgrid.com/NR/rdonlyres/67374C36-1635-42E8-A2B8-B7B8B9AF2408/44739/Z_CompleteGridCode_I4R5.pdf
|title        = the British Grid Code
|access-date  = 3 February 2011
|archive-url  = https://web.archive.org/web/20110322093935/http://www.nationalgrid.com/NR/rdonlyres/67374C36-1635-42E8-A2B8-B7B8B9AF2408/44739/Z_CompleteGridCode_I4R5.pdf
|archive-date = 22 March 2011
|url-status     = dead
|df           = dmy-all
}}</ref> the Supergrid is defined as those parts of the British electricity transmission system that are connected at voltages in excess of 200&nbsp;kV.
The 2.2&nbsp;GW undersea [[Western HVDC Link]] from Scotland to North Wales was built in 2013–2018.<ref name="westernhvdclink1">{{cite web|url=http://www.westernhvdclink.co.uk/news-detail.aspx?newsID=120 |title=Western Link |publisher=National Grid & Scottish Power |access-date=2019-06-18}}</ref> This was the first major non-[[alternating current]] grid link within Great Britain, although interconnectors to foreign grids already used [[HVDC]].
In 2021 a new non-lattice design of electricity pylon, the T-pylon, was built near [[East Huntspill]], Somerset for the new 35 mile [[Hinkley Point C]] to [[Avonmouth]] connection.<ref name=bos-20210914>{{cite news |url=https://www.burnham-on-sea.com/news/photos-national-grid-builds-worlds-first-t-shaped-power-pylon-in-east-huntspill/ |title=National Grid builds UK's first T-pylon in East Huntspill as Hinkley work progresses |website=Burnham-On-Sea.com |date=14 September 2021 |access-date=16 September 2021}}</ref>
In 2023, the National Grid began removing equipment from China's [[NARI Technology]] over national security concerns.<ref>{{Cite web |date=17 December 2023 |title=National Grid drops Beijing-backed supplier over UK power network fears |url=https://www.ft.com/content/0a9887be-87df-4dcc-bdf5-38ee31cfe6b8 |url-access=subscription |access-date=2023-12-17 |website=[[Financial Times]]}}</ref>
==Characteristics of the grid==
[[File:Electricity-production-by-sourceUK1985-2020.svg|thumb|UK electricity production by source 1985–2020<ref>{{cite web |title=Electricity production by source |url=https://ourworldindata.org/grapher/electricity-production-by-source?country=~GBR |website=Our World in Data}}</ref><ref>{{cite web|url=http://www.eia.gov/cfapps/ipdbproject/iedindex3.cfm?tid=2&pid=2&aid=12&cid=all,&syid=1980&eyid=2011&unit=BKWH |title=International Energy Statistics – EIA |website=Eia.gov |access-date=2016-08-21}}</ref><ref>{{cite web|last=|first=|date=31 March 2016|title=UK Energy Statistics, 2015 & Q4 2015|url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/513244/Press_Notice_March_2016.pdf|url-status=dead|archive-url=https://web.archive.org/web/20160703213024/https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/513244/Press_Notice_March_2016.pdf|archive-date=3 July 2016|website=GOV.UK|publisher=Department of Energy & Climate Change|via=Internet Archive}}</ref><ref>{{cite web|last=|first=|date=27 March 2014|title=UK Energy Statistics|url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/296183/pn_march_14.pdf|url-status=dead|archive-url=https://web.archive.org/web/20161008175750/https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/296183/pn_march_14.pdf|archive-date=8 October 2016|website=GOV.UK|publisher=Department of Energy & Climate Change|via=Internet Archive}}</ref><ref>{{Cite web|url=https://www.gov.uk/government/statistics/electricity-section-5-energy-trends|title=Energy Trends: UK electricity|website=GOV.UK|date=30 November 2023 }}</ref>]]
[[File:UK historical net electricity supplied.svg|thumb|Electricity supplied (net) 1920–2014<ref>{{cite web|url=https://www.gov.uk/government/statistical-data-sets/historical-electricity-data-1920-to-2011 |title=Historical electricity data |access-date=14 May 2016}}</ref>]]
{{external media
| topic  =
| float  =right
| image1 =[https://app.electricitymap.org/zone/GB?wind=true&solar=false&remote=true Current grid status, maps]
| image2 =[https://grid.iamkate.com/ Current grid status, charts]
}}
The contiguous synchronous grid covers England (including the [[Isle of Wight]]), [[Scotland]] (including some of the Scottish islands such as [[Orkney]], [[Skye]]<ref>{{Cite web|url=https://www.ssen-transmission.co.uk/news-views/articles/2017/3/over-the-hills-to-skye/ |title=Over the hills to Skye|website=Over the hills to Skye}}</ref> and the [[Western Isles]] which have limited connectivity<ref>{{Cite web|url=http://www.insider.co.uk/news/national-grid-connection-vital-scottish-9894215 |title=National Grid connection 'vital' for Scottish islands' renewables development|first=Scott|last=McCulloch |date=8 March 2016|website=businessInsider}}</ref>), [[Wales]], and the [[Isle of Man]].
===Network size===
The following figures are taken from the 2005 Seven Year Statement.<ref>{{Cite web|url=http://www.nationalgrid.com/uk/library/documents/sys05/default.asp |url-status=dead|archive-url= https://archive.today/20120908194706/http://www.nationalgrid.com/uk/library/documents/sys05/default.asp?sNode=SYS&action=&Exp=Y |archive-date=8 September 2012|title=National Grid - SYS 2005 -|access-date=9 January 2006}}</ref>
* Maximum demand (2005/6): 63&nbsp;[[gigawatt|GW]] (approx.) (81.39% of capacity)
* Minimum demand (2020 May): 15.3&nbsp;GW<ref>{{cite web |last1=Edwardes-Evans |first1=Henry |title=UK electricity demand close to record low Sunday: National Grid |url=https://www.spglobal.com/platts/en/market-insights/latest-news/electric-power/051120-uk-electricity-demand-close-to-record-low-sunday-national-grid |website=www.spglobal.com |archive-url= https://web.archive.org/web/20210303082107/https://www.spglobal.com/platts/en/market-insights/latest-news/electric-power/051120-uk-electricity-demand-close-to-record-low-sunday-national-grid |archive-date=2021-03-03 |language=en |date=11 May 2020 |url-status=live}}</ref>
* Annual electrical energy used in the UK is around {{convert|360|TWh|EJ|abbr=on}}
* Capacity (2005/6): 79.9&nbsp;GW (or 80&nbsp;GW per the 2008 Seven Year Statement)<ref>[http://www.nationalgrid.com/uk/Electricity/SYS/current//electricitycapacity.html] {{dead link|date=August 2016}}</ref>
* Number of large [[power station]]s connected to it: 181
* Length of 400&nbsp;kV grid: 11,500&nbsp;km (circuit)
* Length of 275&nbsp;kV grid: 9,800&nbsp;km (circuit)
* Length of 132&nbsp;kV (or lower) grid; 5,250&nbsp;km (circuit)
Total generating capacity is supplied roughly equally by [[Renewable energy in the United Kingdom|renewable]], [[fossil fuel power plant|gas]] fired, [[nuclear power|nuclear]], [[fossil fuel power plant|coal]] fired [[power stations]]. Annual [[secondary energy|energy transmitted]] in the UK grid is around {{convert|300-360|TWh|EJ|abbr=on}}, with an average load factor of 72% (i.e. 3.6×10<sup>11</sup>/(8,760 × 57×10<sup>6</sup>).{{Update inline|reason=Electricity production form coal has dropped significantly over the last few years - [[Energy in the United Kingdom]] says coal accounted for 5.4% of generation  in 2018|date=October 2019}}
=== Decarbonisation ===
The National Grid has a [[Goal_setting#Stretch_goals|stretch target]] to be [[carbon neutral]] or negative by 2033,<ref>{{cite web |author=Sarah Green |date=27 July 2020 |title=National Grid: UK's electricity system could go carbon-negative from 2033 |url=https://www.edie.net/news/6/National-Grid--UK-s-electricity-system-could-go-carbon-negative-from-2033/ |access-date=11 February 2021 |work=edie.net}}</ref> well ahead of the UK's national target to achieve this by 2050. It also aims to have the capability to be 'zero carbon' as early as 2025, meaning that if energy suppliers are able to produce sufficient green power, the grid could theoretically run without any [[greenhouse gas emissions]] at all (i.e. no [[Carbon capture and storage|carbon capture]] or offsetting would be needed as is the case with 'net zero').<ref>{{cite web |date=April 2020 |title=Zero-carbon explained |url=https://www.nationalgrideso.com/electricity-explained/zero-carbon-explained |access-date=11 February 2021}}</ref> In 2020, about 40% of the grid's energy came from burning natural gas, and it was not expected that anywhere close to sufficient green power would be available to run the grid on zero carbon in 2025, except perhaps on the very windiest days. Analysts such as Hartree Solutions considered in 2020 that getting to 'net zero' by 2050 would be challenging, even more so to reach 'net zero' by 2033.<ref>{{cite web |author=Adam Lewis |date=8 December 2020 |title=Carbon in UK Power – Part 1: Lower Costs or Least Carbon? |url=https://www.hartreesolutions.com/2020/12/08/carbon-in-uk-power-part-1-lower-costs-or-least-carbon/ |access-date=17 February 2021 |work=Hartree Solutions}}</ref><ref>{{cite web |author=Adam Lewis |date=22 December 2020 |title=Carbon in UK Power – Part 2: Is It Time to Prioritise Carbon Over Price? |url=https://www.hartreesolutions.com/2020/12/22/carbon-in-uk-power-part-2-is-it-time-to-prioritise-carbon-over-price/ |access-date=17 February 2021 |work=Hartree Solutions}}</ref>
There has, however, been sustained progress towards [[carbon neutrality]], with [[carbon intensity]] falling by 53% in the five years to 2020. The [[List of active coal-fired power stations in the United Kingdom#Phase-out of coal in the United Kingdom|phase-out of coal]] has been completed: in 2020, only 1.6% of the UK's electricity came from coal, compared with about 25% in 2015. 2020 also saw the UK go more than two months without needing to burn any coal for electricity, the longest period since the [[Industrial Revolution]].<ref>{{cite web|url= https://www.bloomberg.com/news/articles/2020-12-29/u-k-power-grid-heads-for-greenest-year-with-renewables-growth |title= U.K. Power Grid Heads for Greenest Year as Renewables Grow|work= [[Bloomberg News|bloomberg]]|author=Rachel Morison|date = 29 December 2020|access-date=11 February 2021}}</ref><ref>{{cite web |author= |date=11 January 2021 |title=Britain sees greenest year for electricity in 2020 – National Grid |url=https://www.reuters.com/article/uk-britain-electricity-idUSKBN29G1CB |access-date=11 February 2021 |work=[[reuters]]}}</ref><ref>{{cite web|url= https://www.nhm.ac.uk/discover/news/2020/june/britain-goes-two-months-without-burning-coal.html |title= Britain goes two months without burning coal amid lockdown|work= [[Natural History Museum, London]]|author= Katie Pavid|date = 15 June 2020|access-date=11 February 2021}}</ref> On 30 September 2024, on the closure of the last coal-fired power station, UK electricity became entirely coal-free.<ref>{{Cite web |date=2024-09-30 |title=UK to close last coal power station after 142 years |url=https://www.bbc.co.uk/news/articles/c5y35qz73n8o |access-date=2024-12-01 |website=BBC News |language=en-GB}}</ref>
===Losses===
Figures are again from the 2005 Seven Year Statement.
* [[Joule heating]] in cables: 857.8&nbsp;MW
* Fixed losses: 266&nbsp;MW (consists of [[Corona discharge|corona]] and [[Core loss|iron loss]]; can be 100&nbsp;MW higher in adverse weather)
* Substation transformer heating losses: 142.4&nbsp;MW
* Generator transformer heating losses: 157.3&nbsp;MW
* Total losses: 1,423.5&nbsp;MW (2.29% of peak demand)
Although overall losses in the National Grid are low, there are significant further losses in onward [[electricity distribution]] to the consumer, causing a total distribution loss of about 7.7%.{{Citation needed|date=October 2021}} Losses differ significantly for customers connected at different voltages; connected at high voltage the total losses are about 2.6%, at medium voltage 6.4% and at low voltage 12.2%.<ref name=chpa-200510>{{cite web |page=6 |url=http://www.chpa.co.uk/news/reports_pubs/Time%20to%20Take%20a%20Fresh%20Look%20at%20CHP%20October%202005.pdf |title=Time to Take a Fresh Look at CHP... |last=Minett |first=Simon |website=DELTA Energy and Environment |date=October 2005 |archive-url=https://web.archive.org/web/20080227185949/http://www.chpa.co.uk/news/reports_pubs/Time%20to%20Take%20a%20Fresh%20Look%20at%20CHP%20October%202005.pdf |archive-date=27 February 2008}}</ref>
Generated power entering the grid is metered at the high-voltage side of the generator transformer.<ref>Metering Code of Practice 1 (Elexon Ltd)</ref><ref>Metering Code of Practice 2</ref> Any power losses in the generator transformer are therefore accounted to the generating company, not to the grid system. The power loss in the generator transformer does not contribute to the grid losses.
===Power flow===
In 2009–10 there was an average power flow of about 11&nbsp;GW from the north of the UK, particularly from Scotland and northern England, to the south of the UK across the grid. This flow was anticipated to grow to about 12&nbsp;GW by 2014.<ref>[http://www.nationalgrid.com/uk/sys_09/default.asp?action=mnch4_16.htm&Node=SYS&Snode=4_16&Exp=Y Effect on Power Transfers] {{Webarchive|url= https://web.archive.org/web/20120728095239/http://www.nationalgrid.com/uk/sys_09/default.asp?action=mnch4_16.htm&Node=SYS&Snode=4_16&Exp=Y |date=28 July 2012 }}, 2009 Seven Year Statement, National Grid</ref> Completion of the [[Western HVDC Link]] in 2018 added capacity for a flow of 2.2 GW between Western Scotland and North Wales.<ref>{{Cite web|url=http://www.westernhvdclink.co.uk/default.aspx |title=Western Link project|website=www.westernhvdclink.co.uk|access-date=10 February 2019}}</ref>
Because of the power loss associated with this north to south flow, the effectiveness and efficiency of new generation capacity is significantly affected by its location. For example, new generating capacity on the south coast has about 12% greater effectiveness due to reduced transmission system power losses compared to new generating capacity in north England, and about 20% greater effectiveness than in northern Scotland.<ref name="Transmission losses">{{cite web|last=PLC|first=National Grid Company|title=2002 Seven Year Statement|url=http://www.nationalgrid.com/UK/library/documents/sys_02/fla_intro1.htm |work=National Grid – UK – Library|publisher=National Grid|access-date=8 November 2013|archive-url= https://web.archive.org/web/20051219140237/http://www.nationalgrid.com/uk/library/documents/sys_02/fla_intro1.htm |archive-date=19 December 2005|url-status=dead|df=dmy-all}}</ref>
===Interconnectors===
[[Image:HVDC Europe.svg|thumb|right|upright=1.6|
{{legend|#F80E34|Existing links}}
{{legend|#10BF45|Under construction}}
{{legend|#0E25F8|Proposed}}
Some of these HVDC lines transfer power from renewable sources such as hydro and wind. For names, see also the [[List of HVDC projects#Maps|annotated version.]]{{Update inline|reason=many colors incorrect|date=February 2021}}]]
There is a 40 MW AC cable to the Isle of Man, the [[Isle of Man to England Interconnector]] and a 260km 600MW HVDC cable to the [[Shetland Islands]].<ref>https://www.ssen-transmission.co.uk/projects/project-map/shetland/</ref>
The UK grid is connected to adjacent European electrical grids by [[submarine power cable]]s.
In 2014, the UK's [[Synchronous grid of Continental Europe#List of electricity interconnection levels|electricity interconnection level]] (off-island transmission capacity relative to production capacity) was 6%<!-- 4 GW? -->.<ref name=eil>COM/2015/082 final: "Achieving the 10% electricity interconnection target" [http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=COM:2015:0082:FIN Text] [http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52015DC0082&from=EN PDF] page 2-5. ''[[European Commission]]'', 25 February 2015. [https://web.archive.org/web/20151225022701/http://ec.europa.eu/priorities/energy-union/docs/interconnectors_en.pdf Archive] [https://www.eumonitor.eu/9353000/1/j4nvhdfdk3hydzq_j9vvik7m1c3gyxp/vjs4eawsiryh Mirror]</ref><!--several upgrades since then-->
{{As of|2024}}, the total capacity of these connectors is over 9 GW<!--simple math gives 9.8, but some is used as reserve-->.{{Citation needed|date=July 2022}} They include direct-current cables to northern France (2 GW [[HVDC Cross-Channel]], 1 GW HVDC [[IFA-2]], 1 GW [[ElecLink]] via the [[Channel Tunnel]]<ref>{{Cite web|date=15 October 2020|title=ElecLink: IGC approves start of tests at the converter stations|url= https://press.getlinkgroup.com/news/eleclink-igc-approves-start-of-tests-at-the-converter-stations-7498-0791e.html |access-date=2021-09-09|website=[[Getlink]]|language=en}}</ref>); Belgium (1 GW HVDC [[Nemo Link]]); the Netherlands (1 GW HVDC [[BritNed]]); Norway (1.4 GW HDVC [[North Sea Link]]); Northern Ireland (500 MW HVDC [[Moyle Interconnector]]); the Republic of Ireland (500 MW HVDC [[East–West Interconnector]]), and Denmark (1.4&nbsp;GW [[Viking Link]]).
A further 500&nbsp;MW link with the Republic of Ireland ([[Greenlink]]) is scheduled for 2024.<ref>{{Cite web|last=Stanford|first=Anna |date=2021-09-21|title=Siemens Energy and Sumitomo Electric awarded EPC contract for Ireland-UK interconnector|url= https://www.greenlink.ie/post/siemens-energy-and-sumitomo-electric-awarded-epc-contract-for-ireland-uk-interconnector |access-date=2021-09-23|website=Greenlink|language=en}}</ref> Further potential schemes include links with Germany ([[NeuConnect]], 1.4&nbsp;GW); Iceland ([[Icelink]], around 1&nbsp;GW)<ref>{{cite web |url=http://www2.nationalgrid.com/About-us/European-business-development/Interconnectors/Iceland/ |title=Interconnectors: Iceland |publisher=National Grid |date=2016-07-12 |access-date=2016-08-21 |archive-url= https://web.archive.org/web/20160721053342/http://www2.nationalgrid.com/About-us/European-business-development/Interconnectors/Iceland/ |archive-date=21 July 2016 |url-status=dead |df=dmy-all }}</ref> and [[Xlinks Morocco-UK Power Project|Morocco]] (3.6&nbsp;GW from new battery-backed solar generation).<ref>{{Cite web|last=Grundy|first=Alice |date=2021-09-25|title=Moroccan solar-plus-wind to be linked to GB in 'ground-breaking' Xlinks project|url=https://www.current-news.co.uk/news/moroccan-solar-plus-wind-to-be-linked-to-gb-in-ground-breaking-xlinks-project |access-date=2021-09-29|website=Current}}</ref>
===Grid storage===
The UK grid has access to large pumped storage systems, notably [[Dinorwig Power Station]] which can provide 1.7 GW for 5–6 hours, and the smaller [[Cruachan Power Station|Cruachan]] and [[Ffestiniog Power Station|Ffestiniog]].
There are also some [[Battery storage power station|grid batteries]]. As of May 2021, 1.3 GW of battery storage was operating in the United Kingdom, with 16&nbsp;GW of projects in the pipeline potentially deployable over the next few years.<ref name=solarpowerportal-20210519>{{cite news |url=https://www.solarpowerportal.co.uk/blogs/top_ten_uk_battery_storage_projects_forecast_for_2021_completion |title=Top ten UK battery storage projects forecast for 2021 completion |last=McCorkindale |first=Mollie |website=Solar Power Portal |date=19 May 2021 |access-date=27 September 2021}}</ref> A 100&nbsp;MW power Chinese-financed plant at [[Minety]], Wiltshire was reported to be the largest in Europe when it opened in July 2021;<ref>{{Cite news|date=2021-07-15|title=Biggest storage battery in Europe built near Wiltshire village|language=en-GB|work=BBC News|url=https://www.bbc.com/news/uk-england-bristol-57847700 |access-date=2021-09-29}}</ref> when a 50&nbsp;MW extension is completed, the site's storage capacity will be 266&nbsp;MWh.<ref name=pensopower-2021>{{cite web |url=https://www.pensopower.com/ |title=About |website=Penso Power |year=2021 |access-date=27 September 2021}}</ref>
===Reserve services and frequency response===
{{main|National Grid Reserve Service}}
National Grid is responsible for contracting short term generating provision to cover demand prediction errors and sudden failures at power stations. This covers a few hours of operation giving time for market contracts to be established to cover longer term balancing.
The grid frequency is normally maintained within 49.8 and 50.2 Hz.<ref name=LFDD/> [[Frequency-response reserve]]s act to keep the system's [[Alternating current|AC]] frequency within ±1% of 50&nbsp;[[Hertz|Hz]], except in exceptional circumstances. These are used on a second by second basis to either lower the demand or to provide extra generation.<ref name=ng-consultation-june2009>{{citation |chapter-url=http://www.nationalgrid.com/NR/rdonlyres/32879A26-D6F2-4D82-9441-40FB2B0E2E0C/39517/Operatingin2020Consulation1.pdf#page=75 |title=Operating the Electricity Transmission Networks in 2020 – Initial Consultation |chapter=Appendix D Description of Balancing Services |date=June 2009 |publisher=National Grid |access-date=8 January 2011 |archive-url=https://web.archive.org/web/20111223080101/http://www.nationalgrid.com/NR/rdonlyres/32879A26-D6F2-4D82-9441-40FB2B0E2E0C/39517/Operatingin2020Consulation1.pdf#page=75 |archive-date=23 December 2011 |url-status=dead |df=dmy-all }}</ref> In an emergency where the discrepancy between supply and demand is too great and the frequency drops too far (between 48.8 Hz down to 47.8 Hz) then the Low Frequency Demand Disconnection (LFDD) automatic cutouts progressively trigger and remove up to 60% of the customer load from the Supergrid to avoid blacking out the entire grid.<ref name=LFDD>https://www.nationalgrid.co.uk/downloads/4093/6-low-frequency-demand-disconnection.pdf</ref>
Reserve services are a group of services each acting within different response times:<ref name=ng-consultation-june2009 />
* Fast Reserve: rapid delivery (within two minutes) of increased generation or reduced demand, sustainable for a minimum of 15 minutes.
* Fast Start: generation units that start from a standstill and deliver power within five minutes automatically, or within seven minutes of a manual instruction, with generation maintained for a minimum of four hours.
* Demand Management: reduction in demand of at least 25&nbsp;MW from large power users, for at least an hour.
* Short Term Operating Reserve (STOR): generation of at least 3&nbsp;MW, from a single or aggregation of sites, within four hours of instruction and maintained for at least two hours.
* BM Start-Up: mainstream major generation units maintained in either an ''energy readiness'' or ''hot standby'' state.
These reserves are sized according to three factors:<ref name=UKERC-march2006>{{Cite book |url=http://www.ukerc.ac.uk/ResearchProgrammes/TechnologyandPolicyAssessment/TPAProjectIntermittency.aspx |title=The Costs and Impacts of Intermittency |author1=Gross, R |author2=Heptonstall, P |author3=Anderson, D |author4=Green, T |author5=Leach, M |author6=Skea, J |name-list-style=amp |publisher=UK Energy Research Centre |date=March 2006 |isbn=1-903144-04-3 |access-date=15 July 2008 |archive-url=https://web.archive.org/web/20080621194951/http://www.ukerc.ac.uk/ResearchProgrammes/TechnologyandPolicyAssessment/TPAProjectIntermittency.aspx |archive-date=21 June 2008 |url-status=dead |df=dmy-all }}</ref>
* The largest credible single generation failure event, which is currently either [[Sizewell B nuclear power station]] (1,260&nbsp;MW) or one cable of the [[HVDC Cross-Channel]] interconnector (1,000&nbsp;MW)
* The general anticipated availability of all generation plants
* Anticipated demand prediction errors
==Control of the grid==
The English and Welsh parts of the National Grid are controlled from the National Grid Control Centre which is located in St Catherine's Lodge, [[Sindlesham]], [[Wokingham]] in Berkshire.<ref name="agen">{{cite web|url=http://www.nationalgrid.com/NR/rdonlyres/76BA1772-B4B0-4A93-9C84-3286E00DF83F/17155/Agenda_22May_v11.pdf/ |title=Agenda 22 May 2007 |format=PDF |archive-url=https://web.archive.org/web/20110714155430/http://www.nationalgrid.com/NR/rdonlyres/76BA1772-B4B0-4A93-9C84-3286E00DF83F/17155/Agenda_22May_v11.pdf/ |archive-date=14 July 2011 |access-date=3 November 2010 |url-status=dead |df=dmy }}</ref><ref name="neta">{{cite web|url=http://www.nationalgrid.com/NR/rdonlyres/355BBECD-D3B8-4DF7-AFE7-7314FA7B8C28/2407/NETA_Desp_Inst_Guide_Iss_No3_030403.pdf/ |title=NETA Despatch Instruction Guide |format=PDF |archive-url=https://web.archive.org/web/20110714155437/http://www.nationalgrid.com/NR/rdonlyres/355BBECD-D3B8-4DF7-AFE7-7314FA7B8C28/2407/NETA_Desp_Inst_Guide_Iss_No3_030403.pdf/ |archive-date=14 July 2011 |access-date=3 November 2010 |url-status=dead |df=dmy }}</ref><ref name="wind">{{cite web|url=http://www.windturbineratings.com/wind-turbine-price-list-uk/ |title=Wind Turbine Price List Uk |archive-url=https://archive.today/20101103110112/http://www.windturbineratings.com/wind-turbine-price-list-uk/ |archive-date=3 November 2010 |access-date=3 November 2010 |url-status=dead |df=dmy }}</ref><ref name="rmets">{{cite web|url=http://www.rmets.org/events/national-grid-control-centre-visit-0 |title=National Grid Control Centre Visit &#124; Royal Meteorological Society |website=Rmets.org |date=2012-09-24 |access-date=2016-08-21}}</ref> It is sometimes described as being a 'secret' location.<ref>{{cite news|url=https://www.independent.co.uk/arts-entertainment/tv/features/power-struggle-the-national-grid-was-created-to-provide-energy-for-all--but-thats-when-the-problems-really-began-2113229.html |archive-url=https://ghostarchive.org/archive/20220618/https://www.independent.co.uk/arts-entertainment/tv/features/power-struggle-the-national-grid-was-created-to-provide-energy-for-all--but-thats-when-the-problems-really-began-2113229.html |archive-date=18 June 2022 |url-access=subscription |url-status=live |title=Power struggle: The National Grid was created to provide energy for all – but that's when the problems really began |newspaper=[[The Independent]] |access-date=2016-08-21}}</ref> {{asof|2015}} the system is under consistent [[Cyberattack|cyber attack]].<ref>Ward, Jillian. "[https://www.bloomberg.com/news/2015-01-09/power-grid-under-cyber-attack-every-minute-sees-u-k-up-defenses.html U.K. Power Grid is Under Attack From Hackers Every Minute, Says Parliament]" ''Bloomberg'', 9 January 2015. Retrieved: 20 January 2015.</ref>
Although the transmission network in Scotland is owned by separate companies – SP Transmission plc (part of [[ScottishPower]]) in the south, and Scottish Hydro Electric Transmission plc (part of [[Scottish and Southern Electricity Networks]]) in the north<ref>{{Cite web|url=https://www.spenergynetworks.co.uk/pages/our_transmission_network.aspx|title=Our Transmission Network|website=SPEnergyNetworks|language=en|access-date=2020-01-24}}</ref> – overall control rests with National Grid Electricity System Operator.<ref name=":0" />
==Transmission costs==
[[File:Benkid77 Puddington-Shotwick footpath 27 110809.JPG|thumb|400 kV power line in Cheshire]]
The costs of operating the National Grid System are recouped by National Grid Electricity System Operator (NGESO) through levying of Transmission Network Use of System (TNUoS) charges on the users of the system.<ref>{{Cite web|title=Transmission Network Use of System (TNUoS) Charges|url=https://www.nationalgrideso.com/industry-information/charging/transmission-network-use-system-tnuos-charges|access-date=2021-12-08|website=National Grid ESO}}</ref> The costs are split between the generators and the users of electricity.<ref name="claverton-energy1">{{cite web|last=Andrews |first=Dave |url=http://www.claverton-energy.com/what-is-the-cost-per-kwh-of-bulk-transmission-national-grid-in-the-uk-note-this-excludes-distribution-costs.html |title=What is the cost per kWh of bulk transmission / National Grid in the UK (note this excludes distribution costs) &#124; Claverton Group |website=Claverton-energy.com |access-date=2016-08-21}}</ref>
Tariffs are set annually by NGESO, and the country is divided into zones, each with a different tariff for generation and consumption. In general, tariffs are higher for generators in the north and consumers in the south since there is generally a north–south flow of electricity.
===Triad demand===
'Triad demand' is a metric of demand which reports retrospectively three numbers about peak demand between November and February (inclusive) each winter.  In order to encourage usage of the National Grid to be less 'peaky', the triad is used as the basis for extra charges paid by the users (the licensed electricity suppliers) to the National Grid: the users pay less if they can [[Load management|manage their usage]] so as to be less peaky.
For each year's calculation, historic system demand metrics are analysed to determine three half-hour periods of high average demand; the three periods are known as triads. The periods are (a) the period of peak system demand, and (b) two other periods of highest demand which are separated from peak system demand and from each other by at least ten days.
For power stations, the chargeable demand is only the net site demand (per CUSC rule 14.17.10), so when the site is net exporting (i.e. total metered generation at that site exceeds total separately metered station demand), that separately metered station demand shall not be liable for demand TNUoS charges in relation to the station demand at triad.
Triad dates in recent years were:
{| class="wikitable"
! Year !! Triad 1 !! Triad 2 !! Triad 3
|-
| 2015/16 <ref>Inenco, 2015/16 Triads, published 31 March 2016</ref> || Wednesday 25 November 2015, 17:00 – 17:30 || Tuesday 19 January 2016, 17:00–17:30 || Monday 15 February 2016, 18:00–18:30
|-
| 2016/17 <ref>Trident Utilities, [http://www.tridentutilities.co.uk/201617-triad-periods-confirmed/ 2016/17 Triad Periods Confirmed], published 29 March 2017, accessed 3 April 2018</ref>|| Monday 5 December 2016, 17:00 – 17:30 || Thursday 5 January 2017, 17:00 – 17:30 || Monday 23 January 2017, 17:00 – 17:30
|-
| 2017/18 <ref>Stark, [https://www.stark.co.uk/resources/news/tnuos-charges-2018/ History repeats itself: trends are hard to change], published 26 March 2018, accessed 3 April 2018</ref> || Monday 11 December 2017, 17:30 – 18:00 || Monday 26 February 2018, 18:30–19:00 || Monday 5 February 2018, 18:00–18:30
|-
| 2018/19 || || ||
|-
| 2019/20 || || ||
|-
| 2020/21 <ref>Now Then Energy, [https://www.nowthenenergy.co.uk/news/triad2021results Winter 20-21 TRIAD dates announced], published 29 March 2021, accessed 30 April 2021</ref>|| Monday 7 December 2020, 17:00 - 17:30 || Thursday 7 January 2021, 17:30 - 18:00 || Wednesday 10 February 2021, 18:00 - 18:30
|}
This is the main source of income which National Grid uses to cover its costs for high-voltage long-distance transmission (lower voltage distribution is charged separately). The grid also charges an annual fee to cover the cost of generators, distribution networks and large industrial users connecting.
Triad charges encourage users to cut load at peak periods; this is often achieved by using diesel generators. Such generators are also routinely used by National Grid.<ref>{{cite web|last=Andrews |first=Dave |url=http://www.claverton-energy.com/commercial-opportunities-for-back-up-generation-and-load-reduction-via-national-grid-the-national-electricity-transmission-system-operator-netso-for-england-scotland-wales-and-offshore.html |title=Commercial Opportunities for Back-Up Generation and Load Reduction via National Grid, the National Electricity Transmission System Operator (NETSO) for England, Scotland, Wales and Offshore.|website=Claverton-energy.com |access-date=2016-08-21}}</ref>
===Estimating costs per kW⋅h of transmission===
If the total TNUoS or Triad receipts (say £15,000/MW·year × 50,000&nbsp;MW = £750 million/year) is divided by the total number of units delivered by the UK generating system in a year (the total number of units sold – say {{convert|360|TWh|EJ}}.<ref name="claverton-energy1"/>), then a crude estimate can be made of transmission costs, and one gets the figure of around 0.2p/kW⋅h. Other estimates also give a figure of 0.2p/kW⋅h.<ref name="claverton-energy1"/>
However, Bernard Quigg notes: "According to the 06/07 annual accounts for NGC UK transmission, NGC carried 350TW⋅h for an income of £2012m in 2007, i. e. NGC receives 0.66p per kW&nbsp;hour. With two years inflation to 2008/9, say 0.71p per kW⋅h.",<ref>{{cite web|url=http://www.claverton-energy.com/energy-experts-library/downloads/gridoperations |title=Grid Operations &#124; Claverton Group |website=Claverton-energy.com |access-date=2016-08-21}}</ref> but this also includes generators' connection fees.
===Generation charges===
In order to be allowed to supply electricity to the transmission system, generators must be licensed (by BEIS) and enter into a connection agreement with NGET which also grants Transmission Entry Capacity (TEC). Generators contribute to the costs of running the system by paying for TEC, at the generation TNUoS tariffs set by NGET. This is charged on a maximum-capacity basis. In other words, a generator with 100&nbsp;MW of TEC who only generated at a maximum rate of 75&nbsp;MW during the year would still be charged for the full 100&nbsp;MW of TEC.{{Citation needed|date=April 2022}}
In some cases, there are negative TNUoS tariffs. These generators are paid an amount based on their peak net supply over three ''proving runs'' over the course of the year. This represents the reduction in costs caused by having a generator close to the centre of demand of the country.{{Citation needed|date=April 2022}}
National Grid uses a [[grid services]] market. "Dynamic Containment" started in October 2020, initially priced at £17 per MW per hour<!--not MWh-->, and Dynamic Regulation (DR) started in April 2022.<ref>{{cite web |title=National Grid ESO's newest frequency service Dynamic Regulation goes live |url=https://www.current-news.co.uk/news/national-grid-esos-newest-frequency-service-dynamic-regulation-goes-live |website=Current |language=en-gb |date=8 April 2022}}</ref>
===Demand charges===
{{unreferenced section|date=November 2014}}
Consumers of electricity are split into two categories: half-hourly metered (HH) and non-half-hourly metered (NHH). Customers whose peak demand is sufficiently high are obliged to have a HH meter, which, in effect, takes a meter reading every 30 minutes. The rates at which charges are levied on these customers' electricity suppliers therefore varies 17,520 times a (non-leap) year.
The TNUoS charges for a HH metered customer are based on their demand during three half-hour periods of greatest demand between November and February, known as the Triad. Due to the nature of electricity demand in the UK, the three Triad periods always fall in the early evening, and must be separated by at least ten clear working days. The TNUoS charges for a HH customer are simply their average demand during the triad periods multiplied by the tariff for their zone. Therefore, ({{as of|2007|lc=on}}) a customer in London with a 1&nbsp;MW average demand during the three triad periods would pay £19,430 in TNUoS charges.
TNUoS charges levied on NHH metered customers are much simpler. A supplier is charged for the sum of their total consumption between 16:00 and 19:00 every day over a year, multiplied by the relevant tariff.
===Constraint payments===
Constraint payments are payments to generators above a certain size, where the National Grid gives them dispatch instructions that they are unable to take the electricity that the generators would normally provide. This can be due to a lack of transmission capacity, a shortfall in demand, or unexpected excess generation. A constraint payment is recompense for the reduction in generation.<ref>http://ireland2050.ie/questions/what-are-constraint-payments/ What are constraint payments? [[Energy Institute]]</ref>
==Major incidents==
Power cuts due to faults in the national grid, or lack of generation to supply it with sufficient power, are very rare. The overall performance of the system is published on National Grid's website and includes a simple [[High availability|high-level figure for the transmission system availability]]. {{As of|alt=For 2021–22|2022|post=,}} this was 99.999612%.<ref>{{Cite web |title=National Electricity Transmission System Performance Report, 2021-22 |url=https://www.nationalgrideso.com/document/267701/download |access-date=2023-02-04 |website=National Grid ESO}}</ref>
In 2020–21, issues affecting the low voltage distribution networks – for which National Grid is not responsible – caused almost all the 60 minutes or so per year, on average, of unplanned domestic power cuts.<ref>{{Cite web |title=RIIO-1 Electricity Distribution Annual Report 2020-21 |url=https://www.ofgem.gov.uk/publications/riio-1-electricity-distribution-annual-report-2020-21 |access-date=2023-02-04 |date=2022-03-08 |website=Ofgem |language=en}}</ref>
Since 1990, there have been a small number of prominent power outages which were linked to National Grid:
===August 2003===
{{Main page|2003 London blackout}}
In the early evening of 28 August 2003, a power cut affected 476,000 customers in the south London area, as well as the [[London Underground]] and some rail services, for approximately 40 minutes. A total of 724&nbsp;MW of load was lost.
An oil leak had been left untreated, except for top-ups, for many months, pending a proper fix. This caused an alarm which was misinterpreted by the National Grid control room. While switching the presumed faulty equipment out, an incorrectly sized protection relay installed several years prior caused a circuit breaker to trip, resulting in the loss of supply to two major south London substations.
===September 2003===
A week after the London blackout, on 5 September 2003, an incident occurred at Hams Hall substation which affected supply to 201,000 customers <!-- 143,000 Aquila customers and 58,000 EME customers --> in east Birmingham. Affected customers included Network Rail, Birmingham International Airport, and the National Exhibition Centre, with a total of 301&nbsp;MW <!-- Aquila: 213 MW, EME: 88 MW --> of load lost.
This was attributed to an error made by National Grid when commissioning protection systems after upgrading components in the substation that August.<ref name="ofgem2004">{{Cite web |title=Report on support investigations into recent blackouts in London and West Midlands Volume 1 - Main report |date=2004-06-25 |work=[[Ofgem]] |url=https://www.ofgem.gov.uk/sites/default/files/docs/2004/06/sectoralinvestigations-18.pdf}}</ref>
===May 2008===
On 27 May 2008 starting at 11:34, two of Britain's largest power stations, [[Longannet]] in Fife and [[Sizewell B]] in Suffolk, disconnected from the grid ("tripped") within minutes of each other. The total combined loss of generation caused by these trips was at least 1714&nbsp;MW &mdash; larger than the maximum loss of 1260&nbsp;MW which the grid was required to support that day.<ref name="nationalgrid2009">{{Cite web |date=Feb 2009 |title=Report of the National Grid Investigation into the Frequency Deviation and Automatic Demand Disconnection that occurred on the 27th May 2008 |url=http://nationalgrid.com/NR/rdonlyres/E19B4740-C056-4795-A567-91725ECF799B/32165/PublicFrequencyDeviationReport.pdf |archive-url= https://web.archive.org/web/20100104165133/http://nationalgrid.com/NR/rdonlyres/E19B4740-C056-4795-A567-91725ECF799B/32165/PublicFrequencyDeviationReport.pdf |archive-date=2010-01-04 |website=National Grid}}</ref>
The system frequency immediately dropped to 49.2&nbsp;Hz, and subsequent additional trips of generation due to automatic protection caused the frequency to fall further to a low of 48.8&nbsp;Hz. This caused the distribution networks to automatically disconnect some customers in order to arrest the frequency drop, and over the next few hours National Grid ordered the distribution networks to reduce voltage in order to reduce demand. At least 500,000 customers lost power.<ref name="guardian2008">{{cite news
| first1 = Mark
| last1 = Milner
| first2 = Graeme
| last2 = Wearden
| title = Q&A: Blackout Britain
| work = [[The Guardian]]
| date = 28 May 2008
| url = https://www.theguardian.com/business/2008/may/28/power.cuts
}}
</ref><ref>{{cite news
| first1 = Murad
| last1 = Ahmed
| first2 = Steve
| last2 = Hawkes
| title = Blackouts hit thousands as generators fail
| work = [[The Times]]
| date = 28 May 2008
| url = http://www.timesonline.co.uk/tol/news/uk/article4016552.ece
| archive-url = https://web.archive.org/web/20110809144438/http://www.timesonline.co.uk/tol/news/uk/article4016552.ece
| archive-date = 2011-08-09
}}
</ref><ref>{{cite web|author=George South |url=https://www.bbc.co.uk/blogs/ipm/2008/05/blackout_britain.shtml |title=iPM: Blackout Britain? |publisher=BBC |date=2008-05-28 |access-date=2016-08-21}}</ref> Within 40 minutes, distribution networks were allowed to reconnect all customers, although voltage control continued in some areas until 18:07.{{r|nationalgrid2009}}
The incident was described as a "gigantic coincidence" and was not attributed to lack of investment.{{r|guardian2008}} Nonetheless, a number of issues were exposed by the event. The behaviour of generation protection during sudden frequency changes caused a number of generators to disconnect from the grid incorrectly. The Low Frequency Demand Disconnection and voltage control schemes also did not deliver as much demand reduction as they were intended to, but this did not have a significant impact on the outage.{{r|nationalgrid2009}}
===August 2019===
The third event occurred on 9 August 2019, when around a million customers across Great Britain found themselves without power.<ref>{{cite web|url=https://www.bbc.com/news/uk-49300025 |title=Major power failure affects homes and transport |publisher=BBC |date=2019-08-09 |access-date=2019-08-09}}</ref> Lightning struck a transmission line at 4:52 pm, causing the loss of 500 MW embedded (mostly solar) generation. Almost immediately, [[Little Barford Power Station]] and [[Hornsea Wind Farm]] tripped within seconds of each other, removing 1.378 GW of generation, which was in excess of the 1 GW of backup power (the size of the largest single expected loss) that the operator was maintaining at the time.<ref name=preliminary>https://www.nationalgrideso.com/document/151081/download   Interim Report into the Low Frequency Demand Disconnection (LFDD) following Generator Trips and Frequency Excursion on 9 Aug 2019 - 16 August 2019</ref> The grid frequency fell to 48.8&nbsp;Hz before automatic load-shedding disconnected 5% of the local distribution networks (1.1 million customers) for 15 to 20 minutes; this action stabilised the remaining 95% of the system and prevented a wider blackout.<ref>{{cite tweet|number=1159866308500041728|user=enappsys|title=GB : Frequency drops off the chart to...|date=9 August 2019}}</ref><ref name="preliminary"/>
Although power was maintained at all times to the railway network (but not to the signalling system), the reduction in frequency caused 60 [[Thameslink]] [[British Rail Class 700|Class 700]] and [[British Rail Class 717|717]] trains to fail. Half were restarted by the drivers but the others required a technician to come out to the train to restart it.<ref name="preliminary" /> This led to substantial travel disruption for several hours on the [[East Coast Main Line]] and Thameslink services. The supply to [[Newcastle International Airport|Newcastle Airport]] was also disrupted, and a weakness was exposed in backup power arrangements at [[Ipswich Hospital]].<ref name="preliminary"/>
An investigation by [[Ofgem]] concluded in January 2020. It found that Little Barford and Hornsea One had failed to remain connected to the grid following the lightning strike, and their operators – [[RWE npower|RWE]] and [[Ørsted (company)|Ørsted]] respectively – agreed to each pay £4.5 million to Ofgem's redress fund. Additionally, Ofgem fined distribution network operator [[UK Power Networks]] £1.5M for beginning to reconnect customers before being cleared to do so, although this breach of procedure did not affect the recovery of the system.<ref>{{Cite web|url=https://www.current-news.co.uk/news/blackout-investigation-power-firms-fined-as-ofgem-accelerates-eso-review |title=Blackout investigation: Power firms fined as Ofgem 'accelerates' ESO review|last=Stoker|first=Liam |date=3 January 2020|website=Current News|language=en-gb|access-date=2020-01-08}}</ref><ref>{{Cite web|url=https://www.ofgem.gov.uk/publications-and-updates/companies-pay-105-million-over-9-august-power-cut |title=Companies pay £10.5 million over 9 August power cut|date=3 January 2020|website=Ofgem}}</ref>
==Minor incidents==
===November 2015===
On 4 November 2015 National Grid issued an emergency notice asking for voluntary power cuts because of "multiple plant breakdowns". No power cuts occurred but wholesale electricity prices rose dramatically, with the grid paying up to £2,500 per megawatt-hour.<ref>{{cite news|title=National Grid in emergency plea for heavy users to power down|last=Stacey|first=Kiran|author2=Adams, Christopher|date=5 November 2015|work=Financial Times|pages=front page}}</ref>
==See also==
{{div col|colwidth=22em}}
* [[Demand response]]
* [[Cost of electricity by source]]
* [[Economics of nuclear power plants]] – for cost comparisons
* [[Energy security and renewable technology]]
* [[Intermittent energy source]]
* [[TV pickup]]
* [[Walham|2007 switching station flood at Walham, Gloucestershire]]
* [[List of energy storage projects]]
* [[List of major power outages]]
* [[Spark spread]] – calculating the cost of back-up
* [[Load management]]
* [[Three-phase electric power]]
* [[List of HVDC projects]]
* [[List of high voltage underground and submarine cables]]
* [[National Grid Reserve Service]]
* [[Energy in the United Kingdom]]
* [[High-voltage substations in the United Kingdom]]
* [[List of high-voltage transmission links in the United Kingdom]]
{{div col end}}
==References==
{{Reflist}}
==Further reading==
*{{cite book |last=Hannah |first=Leslie |title=Electricity Before Nationalisation, A Study in the Development of the Electricity Supply Industry in Britain to 1948 |year=1979 |location=London & Basingstoke |publisher=[[Macmillan Publishers]] for the [[Electricity Council]] |isbn=0-8018-2145-2 }}
==External links==
{{Commons category}}
* [https://grid.iamkate.com/ National Grid data overview], iamkate.com
* [https://www.earth.org.uk/note-on-UK-grid-CO2-intensity-variations.html Carbon-intensity variations in the GB grid], earth.org.uk
* [https://bmrs.elexon.co.uk/ Real-time electricity market data], Elexon
* [https://web.archive.org/web/20050513000225/http://www.parliament.uk/post/e5.pdf ''UK Electricity Networks: The nature of UK electricity transmission and distribution networks in an intermittent renewable and embedded electricity generation future''], Scott Butler (2001)
* {{usurped|1=[https://web.archive.org/web/20090304090017/http://www.competition-commission.org.uk/rep_pub/reports/1987/fulltext/214c03.pdf ''The electricity supply industry and the Central Electricity Generating Board'']}}, Competition Commission Report (1987)
* [https://news.bbc.co.uk/1/shared/bsp/hi/pdfs/14_06_06_powerstations.pdf Map of GB power stations and national grid], BBC News, map revised by Deloitte & Touche (2003)
* [https://web.archive.org/web/20110606045155/http://www.nationalgrid.com/uk/sys_08/default.asp?Node=SYS&action=mnch6_1.htm&sNode=6&Exp=Y The Transmission System], National Grid's Seven Year Statement (2008)
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{{Energy in the United Kingdom|sources}}
{{Electricity generation}}
{{Use dmy dates|date=April 2016}}
{{DEFAULTSORT:National Grid (Uk)}}
[[Category:National Grid (Great Britain)| ]]
[[Category:Electric power transmission in the United Kingdom]]
[[Category:1933 establishments in the United Kingdom]]
[[Category:Wide area synchronous grids]]