wide area synchronous grid
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A wide area synchronous grid (also called an "interconnection" in
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
) is a
three-phase In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating voltages that are offset in time by one-third of the period. A three-phase system may be arranged in delta (∆) or star (Y) (also ...
electric
power grid An electrical grid is an interconnected network for electricity delivery Electricity delivery is the process that starts after generation of electricity in the power station A power station, also referred to as a power plant and someti ...
that has regional scale or greater that operates at a synchronized
utility frequency The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the e ...
and is electrically tied together during normal system conditions. Also known as ''synchronous zones'', the most powerful is the
synchronous grid of Continental Europe The synchronous grid of Continental Europe (also known as Continental Synchronous Area; formerly known as the UCTE grid) is the largest synchronous electrical grid (by connected power) in the world. It is interconnected as a single phase-locked ...
(ENTSO-E) with 859 
gigawatts The watt (symbol: W) is a unit of Power (physics), power or radiant flux. In the International System of Units (SI), it is defined as a SI derived unit, derived unit of (in SI base units) 1 kg⋅m2⋅s−3 or, equivalently, 1 joule per second. I ...
(GW) of generation, while the widest region served is that of the
IPS/UPS Image:ElectricityUCTE eng.svg, 250px, The synchronous grids of Europe. IPS/UPS is shown in red. The IPS/UPS is a Wide area synchronous grid, wide area synchronous transmission grid of some Commonwealth of Independent States, CIS countries with a co ...
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 European Energy Exchange (EEX) AG is a central European electric power Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt The watt (symbol: W) is ...
(EEX). 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 A high-voltage, direct current (HVDC) electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ...
power transmission line Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ''electrical energy'' refers to energy that has been converted ''fro ...
s (DC ties),
solid-state transformer A solid-state transformer (SST), power electronic transformer (PET), or electronic power transformer is actually an AC-to-AC converter, a type of electric power conversion, electric power converter that replaces a conventional transformer used in a ...
s or
variable-frequency transformer A variable-frequency transformer (VFT) is used to transmit electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In p ...
s (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 are 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. 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; and allow more diverse power generation schemes and permit economies of scale. 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 neighboring synchronous networks make such manipulations more difficult.


Frequency

In a synchronous grid all the generators naturally lock together electrically and run at the same Utility frequency, frequency, and stay very nearly in phase with each other. For rotating generators, a local Governor (device), governor regulates the driving torque, and helps maintain 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 neighboring grids, operating at different frequencies, need to be interconnected, a frequency converter is required. HVDC Interconnectors,
solid-state transformer A solid-state transformer (SST), power electronic transformer (PET), or electronic power transformer is actually an AC-to-AC converter, a type of electric power conversion, electric power converter that replaces a conventional transformer used in a ...
s or
variable-frequency transformer A variable-frequency transformer (VFT) is used to transmit electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In p ...
s links can connect two grids that operate at different frequencies or that are not maintaining synchronism.


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 The synchronous grid of Continental Europe (also known as Continental Synchronous Area; formerly known as the UCTE grid) is the largest synchronous electrical grid (by connected power) in the world. It is interconnected as a single phase-locked ...
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.


Deployed networks

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.When the Grid Was the Grid:The History of North America’s Brief Coast-to-Coast Interconnected Machine -By JULIE COHN
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Planned

* Electricity sector in China, China's electricity suppliers plan to complete by 2020 its ultra high voltage AC synchronous grid linking the current North, Central, and Eastern grids. 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. *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.


DC interconnectors

Interconnectors such as High-voltage direct current lines,
solid-state transformer A solid-state transformer (SST), power electronic transformer (PET), or electronic power transformer is actually an AC-to-AC converter, a type of electric power conversion, electric power converter that replaces a conventional transformer used in a ...
s or
variable-frequency transformer A variable-frequency transformer (VFT) is used to transmit electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In p ...
s can be used to connect two alternating current interconnection networks which are not 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

*High-voltage direct current (HVDC) *Super grid *European super grid *Microgrid *Smart grid *Unified Smart Grid *SuperSmart Grid *Tres Amigas SuperStation


References


External links


A Wide Area Synchronized Frequency Measurement System
{{DEFAULTSORT:Wide Area Synchronous Grid Wide area synchronous grids, * Electric power transmission systems