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 Northern Chinese State Grid with 1,700  gigawatts (GW) of generation capacity, 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]

For physical connections between grids, see Interconnector.
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.

Properties

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.

Frequency

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.

Inertia
Main article: Inertial response

Inertia in a synchronous grid is stored energy that a grid has available which can provide extra power for up to a few seconds to maintain the grid frequency. Historically, this was provided only by the angular momentum of the generators, and gave the control circuits time to adjust their output to variations in loads, and sudden generator or distribution failures.

Inverters connected to HVDC usually have no inertia, but wind power can provide inertia, and solar and battery systems can provide synthetic inertia.[4][5]

Short circuit current

In short circuit situations, it's important for a grid to be able to provide sufficient current to keep the voltage and frequency reasonably stable until circuit breakers can resolve the fault. Many traditional generator systems had wires which could be overloaded for very short periods without damage, but inverters are not as able to deliver multiple times their rated load. The short circuit ratio can be calculated for each point on the grid, and if it is found to be too low, for steps to be taken to increase it to be above 1, which is considered stable.

Timekeeping

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.[6]

Deployed networks
Name Countries Covers/NotesOrganization/CompanyGeneration capacityYearly generationYear/Refs
Northern Chinese State Grid  China Northern ChinaState Grid Corporation of China1700 GW5830 TWh2020[7]
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 millionENTSO-E.859 GW2569 TWh2017[8]
Eastern Interconnection  United States  Canada Eastern US (except most of Texas) and eastern Canada (except Quebec and Newfoundland and Labrador)610 GW1380 TWh2017
Indian National Grid  India Serving over 1.35 billion people404 GW1484 TWh2022[9]
IPS/UPS  Russia  Belarus  Estonia  Latvia  Lithuania  Kazakhstan  Kyrgyzstan  Tajikistan  Georgia  Azerbaijan  Mongolia 11 countries of former Soviet Union serving 240 million337 GW1285 TWh2005[10][11]
China Southern Power Grid  China Chinese southern grid320 GW1051 TWh2019[12]
Western Interconnection  United States  Canada  Mexico Western US, western Canada, and northern Baja California in Mexico265 GW883 TWh2015[13]
National Interconnected System (SIN)  Brazil Electricity sector in Brazil150 GW410 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 people93 GW390 TWh
National Grid (Great Britain)  United Kingdom Great Britain's synchronous zone, serving 65 millionNational Grid plc83 GW

(2018)[14]

 336 TWh2017[14]
Iran National Grid  Iran  Armenia  Turkmenistan Iran and Armenia, serving 84 million people82 GW2019[15]
Southern African Power Pool  Angola  Botswana  Democratic Republic of the Congo  Eswatini  Lesotho  Mozambique  Malawi  Namibia  South Africa  Tanzania  Zambia  Zimbabwe SAPP serves 9 out of 12 SADC countries and small regions of Angola, Malawi, and Tanzania80.9 GW289 TWh2020[16]
Texas Interconnection  United States Most of Texas; serves 24 million customersElectric Reliability Council of Texas (ERCOT)78 GW352 TWh (2016)[17]2018[18]
National Electricity Market  Australia Australia's States and Territories except for Western Australia and the Northern Territory (Tasmania is part of it but not synchronised)National Electricity Market50 GW196 TWh2018[19]
Quebec Interconnection  Canada QuebecHydro-Québec TransÉnergie42 GW184 TWh
Java-Madura-Bali System (JAMALI)  Indonesia JAMALI System serves 7 provinces (West, East, and Central Java, Banten, Jakarta, Yogyakarta, and Bali), serving 49.4 million customers.PLN40.1 GW (2020)[20]163 TWh (2017)[21] 2021
Argentine Interconnection System  Argentina Argentina except Tierra del Fuego39.7 GW129 TWh2019[22]
National Electrical System  Chile Main Chilean grid31.7 GW75.8 TWh2022[23]
Sumatera System  Indonesia Sumatera System serves 8 provinces (North, West, South Sumatera, Aceh, Bengkulu, Lampung, Jambi, and Riau) and Bangka Island, serving 17 million customers PLN 14.7 GW

(2020)[24]

 32.1 TWh

(2016)[24]

 2022[25]
Irish Grid  Ireland  United Kingdom Ireland and Northern Ireland.EirGrid7.3 GW

(2022)[26]

 29.6 TWh2020[27]
SIEPAC  Panama  Costa Rica  Honduras  Nicaragua  El Salvador  Guatemala The Central American Electrical Interconnection System serves Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama6.7 GW2020[28]
Khatulistiwa System  Malaysia  Indonesia Sarawak state and the northwestern part of West Kalimantan (Part of ASEAN Power Grid project) Heads of ASEAN Power Utilities/Authorities (HAPUA) 5.5 GW 2017
South West Interconnected System  Australia Western Australia4.3 GW17.3 TWh2016[29]

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.[30]

Planned
  • China's electricity suppliers plan to complete by 2020 its ultra high voltage AC synchronous grid linking the current North, Central, and Eastern grids.[31] 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.[32]
  • 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 interconnectors
  Existing links
  Under construction
  Proposed
Many of these HVDC lines transfer power from renewable sources such as hydro and wind. For names, see also the annotated version.

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 connections

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

See also

References
  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. Energy un.org
  4. "Inertia and the Power Grid: A Guide Without the Spin".
  5. Inertia and the Power Grid: A Guide Without the Spin Paul Denholm, Trieu Mai, Rick Wallace Kenyon, Ben Kroposki, and Mark O’Malley National Renewable Energy Laboratory
  6. "Serbia, Kosovo power grid row delays European clocks". Reuters. Mar 7, 2018.
  7. "Grid business, SGCC". www.sgcc.com.cn. Retrieved 23 November 2021.
  8. "ENTSO-E Statistical Factsheet 2017" (PDF). www.entsoe.eu. Retrieved 2 January 2019.
  9. Electricity sector in India
  10. 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)
  11. 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)
  12. "Grid business, CSG". www.eng.csg.cn. Retrieved 23 November 2021.
  13. 2016 State of the Interconnection page 10-14 + 18-23. WECC, 2016. Archive
  14. "Digest of UK Energy Statistics (DUKES): electricity". GOV.UK. July 28, 2022.
  15. "Dalahoo Power Plant Adds 310 MW to Power Capacity". Eghtesad Online. 27 November 2019. Retrieved 2019-12-02.
  16. "Annual Reports | Southern African Power Pool". www.sapp.co.zw. Retrieved 2022-12-21.
  17. Ercot 2016 Lists ercot.com
  18. "Quick facts" (PDF). www.ercot.com. 818.
  19. "Electricity supply to regions of the National Electricity Market | Australian Energy Regulator". Archived from the original on 2019-02-09. Retrieved 2019-02-08.
  20. Mulyana, Ridwan Nanda (2021-02-23). Perwitasari, Anna Suci (ed.). "PLN: Ada tambahan 3.000 MW pembangkit listrik di sistem Jawa-Madura-Bali tahun ini". kontan.co.id (in Indonesian). Retrieved 2021-04-24.
  21. synergy (2017-04-28). "Indonesia's Electricity Systems - Jawa-Madura-Bali System". Insights. Retrieved 2021-04-24.
  22. "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.
  23. "Sistema Eléctrico Nacional (SEN) I Coordinador Eléctrico Nacional (CEN)". Coordinador Eléctrico Nacional | Servimos a Chile con Energía (in European Spanish). 2018-07-30. Retrieved 2022-12-21.
  24. synergy (2017-05-29). "Indonesia's Electricity Systems – Sumatera Interconnected System". Insights. Retrieved 2022-11-26.
  25. "PLN Operasikan Sistem Interkoneksi 150 kV Sumatera-Bangka". validnews.id (in Indonesian). Retrieved 2022-11-26.
  26. "Generation capacity statement" (PDF). ltd.uk. Retrieved 21 September 2023.
  27. "Wind Energy Powers Ireland to Renewable Energy Target". 28 Jan 2021.
  28. "Central American Electrical Interconnection System (SIEPAC)" (PDF). IRENA. Retrieved 21 September 2023.
  29. 2015/16 Facts and statistics Western Power
  30. Cohn, Julie (January 2019). "When the Grid Was the Grid: The History of North America's Brief Coast-to Coast Interconnected Machine". Proceedings of the IEEE. 107 (1): 232–243. doi:10.1109/JPROC.2018.2880938. S2CID 58005728.
  31. 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)
  32. 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)
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