Wide area synchronous grid

A wide area synchronous grid (also called an "interconnection" in North America) is a three-phase electric power grid that has regional scale or greater that operates at a synchronized utility frequency and is electrically tied together during normal system conditions. Also known as synchronous zones, the most powerful is the synchronous grid of Continental Europe (ENTSO-E) with 859 gigawatts (GW) of generation, while the widest region served is that of the IPS/UPS system serving most countries of the former Soviet Union. Synchronous grids with ample capacity facilitate electricity trading across wide areas. In the ENTSO-E in 2008, over 350,000 megawatt hours were sold per day on the European Energy Exchange (EEX).[1]

Major WASGs in Eurasia, Africa and Oceania, North and Central America
The two major and three minor interconnections of North America
The synchronous grids of Europe and North Africa

Neighbouring interconnections with the same frequency and standards can be synchronized and directly connected to form a larger interconnection, or they may share power without synchronization via high-voltage direct current power transmission lines (DC ties), solid-state transformers or variable-frequency transformers (VFTs), which permit a controlled flow of energy while also functionally isolating the independent AC frequencies of each side. Each of the interconnects in North America is synchronized at a nominal 60 Hz, while those of Europe run at 50 Hz.

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.[2]

One disadvantage of a wide-area synchronous grid is that problems in one part can have repercussions across the whole grid.


Wide area synchronous networks improve reliability and permit the pooling of resources. Also, they can level out the load, which reduces the required generating capacity, allow more environmentally-friendly power to be employed; allow more diverse power generation schemes and permit economies of scale.[3]

Unusually for a national grid, different regions of Japan's electricity transmission network run at completely different frequencies.

Wide area synchronous networks cannot be formed if the two networks to be linked are running at different frequencies or have significantly different standards. For example, in Japan, for historical reasons, the northern part of the country operates on 50 Hz, but the southern part uses 60 Hz. That makes it impossible to form a single synchronous network, which was problematic when the Fukushima Daiichi plant melted down.

Also, even when the networks have compatible standards, failure modes can be problematic. Phase and current limitations can be reached, which can cause widespread outages. The issues are sometimes solved by adding HVDC links within the network to permit greater control during off-nominal events.

As was discovered in the California electricity crisis, there can be strong incentives among some market traders to create deliberate congestion and poor management of generation capacity on an interconnection network to inflate prices. Increasing transmission capacity and expanding the market by uniting with neighbouring synchronous networks make such manipulations more difficult.


In a synchronous grid, all the generators naturally lock together electrically and run at the same frequency, and stay very nearly in phase with each other. For rotating generators, a local governor regulates the driving torque and helps maintain a more or less constant speed as loading changes. Droop speed control ensures that multiple parallel generators share load changes in proportion to their rating. Generation and consumption must be balanced across the entire grid because energy is consumed as it is produced. Energy is stored in the immediate short term by the rotational kinetic energy of the generators.

Small deviations from the nominal system frequency are very important in regulating individual generators and assessing the equilibrium of the grid as a whole. When the grid is heavily loaded, the frequency slows, and governors adjust their generators so that more power is output (droop speed control). When the grid is lightly loaded the grid frequency runs above the nominal frequency, and this is taken as an indication by Automatic Generation Control systems across the network that generators should reduce their output.

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.

Where neighbouring grids, operating at different frequencies, need to be interconnected, a frequency converter is required. HVDC Interconnectors, solid-state transformers or variable-frequency transformers links can connect two grids that operate at different frequencies or that are not maintaining synchronism.


For timekeeping purposes, over the course of a day the operating frequency will be varied so as to balance out deviations and to prevent line-operated clocks from gaining or losing significant time by ensuring there are 4.32 million on 50 Hz, and 5.184 million cycles on 60 Hz systems each day.

This can, rarely, lead to problems. In 2018 Kosovo used more power than it generated due to a row with Serbia, leading to the phase in the whole synchronous grid of Continental Europe lagging behind what it should have been. The frequency dropped to 49.996 Hz. Over time, this caused synchronous electric clocks to become six minutes slow until the disagreement was resolved.[4]

Deployed networksEdit

Name Covers Organization Generation capacity Yearly generation Year/Refs
Northern Chinese State Grid   China Northern China State Grid Corporation of China 875 GW 5830 TWh 2020[5]
Continental Europe   EU (minus Ireland, Sweden, Finland, Lithuania, Latvia, Estonia, and Cyprus)   Bosnia and Herzegovina   Montenegro   North Macedonia   Serbia    Switzerland   Morocco   Algeria   Tunisia   Turkey   Ukraine   Moldova 24 European countries, serving 450 million ENTSO-E. 859 GW 2569 TWh 2017[6]
Eastern Interconnection   United States   Canada Eastern US (except most of Texas) and eastern Canada (except Quebec and Newfoundland and Labrador) 610 GW
Indian National Grid   India India serving over a billion people 370.5 GW 1236 TWh 2017[7]
IPS/UPS   Russia   Belarus   Estonia   Latvia   Lithuania   Kazakhstan   Kyrgyzstan   Tajikistan   Georgia   Azerbaijan   Mongolia 11 countries of former Soviet Union serving 240 million 337 GW 1285 TWh 2005[8][9]
China Southern Power Grid   China Chinese southern grid 320 GW 1051 TWh 2019[10]
Western Interconnection   United States   Canada   Mexico Western US, western Canada, and northern Baja California in Mexico 265 GW 883 TWh 2015[11]
National Interconnected System (SIN)   Brazil Electricity sector in Brazil 150.3 GW 410 TWh (2007) 2016
Synchronous grid of Northern Europe   Norway   Sweden   Finland   Denmark Nordic countries (Finland, Sweden-except Gotland, Norway and Eastern Denmark) serving 25 million people 93 GW 390 TWh
National Grid (Great Britain)   United Kingdom Great Britain's synchronous zone, serving 65 million. National Grid plc 83 GW (2018)[12] 336 TWh 2017[12]
Iran National Grid   Iran   Armenia   Turkmenistan Iran and Armenia, serving 84 million people 82 GW 2019[13]
Texas Interconnection   United States Most of Texas; serves 24 million customers Electric Reliability Council of Texas (ERCOT) 78 GW 352 TWh (2016)[14] 2018[15]
National Electricity Market   Australia Australia's States and Territories except Western Australia and the Northern Territory. (Tasmania is part of it but not synchronised) National Electricity Market 50 GW 196 TWh 2018[16]
Quebec Interconnection   Canada Quebec 42 GW 184 TWh
Java-Madura-Bali Interconnection (JAMALI)   Indonesia JAMALI System serves 7 provinces (West, East, and Central Java, Banten, Jakarta, Yogyakarta, and Bali). PLN, serving 49.4 million customers. 40.1 GW (2020)[17] 163 TWh (2017)[18] 2021
Argentine Interconnection System   Argentina Argentina except Tierra del Fuego. 129 TWh 2019[19]
SIEPAC   Panama   Costa Rica   Honduras   Nicaragua   El Salvador   Guatemala The Central American Electrical Interconnection System serves Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama.
Southern African Power Pool   Angola   Botswana   Democratic Republic of the Congo   Eswatini   Lesotho   Mozambique   Mali   Namibia   South Africa   Tanzania   Zambia   Zimbabwe SAPP serves 12 countries in Southern Africa.
Irish Grid   Ireland   United Kingdom Ireland and Northern Ireland. EirGrid 29.6 TWh (2020) [20]
South West Interconnected System   Australia Western Australia 17.3 TWh 2016[21]
Sistema Interconectado Central   Chile Main Chilean grid 12.9 GW 2011[22]

A partial table of some of the larger interconnections.

Historically, on the North American power transmission grid the Eastern and Western Interconnections were directly connected, and was at the time largest synchronous grid in the world, but this was found to be unstable, and they are now only DC interconnected.[23]


  • China's electricity suppliers plan to complete by 2020 its ultra high voltage AC synchronous grid linking the current North, Central, and Eastern grids.[24] When complete, its generation capacity will dwarf that of the UCTE Interconnection.
  • Union of the UCTE and IPS/UPS grid unifying 36 countries across 13 time zones.[25]
  • Unified Smart Grid unification of the US interconnections into a single grid with smart grid features.
  • SuperSmart Grid a similar mega grid proposal linking UCTE, IPS/UPS, North Africa and Turkish networks.
  • ASEAN Power Grid plan to connect all ASEAN Grids. The first step is connecting all mainland ASEAN countries with Sumatra, Java, and Singapore Grid, then Borneo Island and Philippines.

DC interconnectorsEdit

  Existing links
  Under construction
Many of these HVDC lines transfer power from renewable sources such as hydro and wind. For names, see also the annotated version.[needs update]

Interconnectors such as High-voltage direct current lines, solid-state transformers or variable-frequency transformers can be used to connect two alternating current interconnection networks which are not necessarily synchronized with each other. This provides the benefit of interconnection without the need to synchronize an even wider area. For example, compare the wide area synchronous grid map of Europe (in the introduction) with the map of HVDC lines (here to the right). Solid state transformers have larger losses than conventional transformers, but DC lines lack reactive impedance and overall HVDC lines have lower losses sending power over long distances within a synchronous grid, or between them.

Planned non-synchronous connectionsEdit

The Tres Amigas SuperStation aims to enable energy transfers and trading between the Eastern Interconnection and Western Interconnection using 30GW HVDC Interconnectors.

See alsoEdit


  1. ^ "EEX Market Monitor Q3/2008" (PDF). Leipzig: Market Surveillance (HÜSt) group of the European Energy Exchange. 2008-10-30: 4. Archived from the original (PDF) on 2011-07-10. Retrieved 2008-12-06. {{cite journal}}: Cite journal requires |journal= (help)
  2. ^ Haubrich, Hans-Jürgen; Dieter Denzel (2008-10-23). "Characteristics of interconnected operation" (PDF). Operation of Interconnected Power Systems (PDF). Aachen: Institute for Electrical Equipment and Power Plants (IAEW) at RWTH Aachen University. p. 3. Archived from the original (PDF) on 2011-07-19. Retrieved 2008-12-06. (See "Operation of Power Systems" link for title page and table of contents.)
  3. ^ https://www.un.org/esa/sustdev/publications/energy/chapter2.pdf[bare URL PDF]
  4. ^ "Serbia, Kosovo power grid row delays European clocks". Reuters. Mar 7, 2018.
  5. ^ "Grid business, SGCC". www.sgcc.com.cn. Retrieved 23 November 2021.
  6. ^ "ENTSO-E Statistical Factsheet 2017" (PDF). www.entsoe.eu. Retrieved 2 January 2019.
  7. ^ Electricity sector in India
  8. ^ UCTE-IPSUPS Study Group (2008-12-07). "Feasibility Study: Synchronous Interconnection of the IPS/UPS with the UCTE". TEN-Energy programme of the European Commission: 2. {{cite journal}}: Cite journal requires |journal= (help)
  9. ^ Sergei Lebed RAO UES (2005-04-20). "IPS/UPS Overview" (PDF). Brussels: UCTE-IPSUPS Study presentation: 4. Retrieved 2008-12-07. {{cite journal}}: Cite journal requires |journal= (help)
  10. ^ "Grid business, CSG". www.eng.csg.cn. Retrieved 23 November 2021.
  11. ^ 2016 State of the Interconnection page 10-14 + 18-23. WECC, 2016. Archive
  12. ^ a b "Digest of UK Energy Statistics (DUKES): Electricity".
  13. ^ "Dalahoo Power Plant Adds 310 MW to Power Capacity". Eghtesad Online. Retrieved 2019-12-02.
  14. ^ http://www.ercot.com/content/wcm/lists/89476/ERCOT2016D_E.xlsx[bare URL spreadsheet file]
  15. ^ "Quick facts" (PDF). www.ercot.com. 818.
  16. ^ "Archived copy". Archived from the original on 2019-02-09. Retrieved 2019-02-08.{{cite web}}: CS1 maint: archived copy as title (link)
  17. ^ Mediatama, Grahanusa (2021-02-23). "PLN: Ada tambahan 3.000 MW pembangkit listrik di sistem Jawa-Madura-Bali tahun ini". kontan.co.id (in Indonesian). Retrieved 2021-04-24.
  18. ^ synergy (2017-04-28). "Indonesia's Electricity Systems - Jawa-Madura-Bali System". Insights. Retrieved 2021-04-24.
  19. ^ "Informe anual 2019" [2019 Annual report]. portalweb.cammesa.com (in Spanish). Compañía Administradora del Mercado Mayorista Eléctrico Sociedad Anónima. 12 June 2020. Retrieved 2020-08-10.
  20. ^ "Wind Energy Powers Ireland to Renewable Energy Target". 28 Jan 2021.
  21. ^ https://westernpower.com.au/media/2308/facts-and-statistics-2015-16.pdf[bare URL PDF]
  22. ^ SIC installed capacity. Central Energía. Retrieved: 15-05-2012
  23. ^ When the Grid Was the Grid:The History of North America’s Brief Coast-to-Coast Interconnected Machine -By JULIE COHN
  24. ^ Liu Zhengya President of SGCC (2006-11-29). "Address at the 2006 International Conference of UHV Transmission Technology". Beijing: UCTE-IPSUPS Study presentation. Retrieved 2006-12-06. {{cite journal}}: Cite journal requires |journal= (help)
  25. ^ Sergey Kouzmin UES of Russia (2006-04-05). "Synchronous Interconnection of IPS/UPS with UCTE - Study Overview" (PDF). Bucharest, Romania: Black Sea Energy Conference: 2. Archived from the original (PDF) on 2013-05-22. Retrieved 2008-12-07. {{cite journal}}: Cite journal requires |journal= (help)

External linksEdit