Super grid
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Super grid

A super grid or supergrid is a wide-area transmission network, generally trans-continental or multinational, that is intended to make possible the trade of high volumes of electricity across great distances. It is sometimes also referred to as a "mega grid". Super grids typically are proposed to use high-voltage direct current (HVDC) to transmit electricity long distances. The latest generation of HVDC power lines can transmit energy with losses of only 1.6% per 1,000 km (621.4 miles).

Super grids could support a global energy transition by smoothing local fluctuations of wind energy and solar energy. In this context they are considered as a key technology to mitigate global warming.

The idea of creating long-distance transmission lines in order to take advantage of renewable sources distantly located is not new. In the US in the 1950s, a proposal was made to ship hydroelectric power from dams being constructed in the Pacific Northwest to consumers in Southern California, but it was opposed and scrapped. In 1961, U.S. president John F. Kennedy authorized a large public works project using new high-voltage, direct current technology from Sweden. The project was undertaken as a close collaboration between General Electric of the U.S. and ASEA of Sweden, and the system was commissioned in 1970. With several upgrades of the converter stations in the intervening decades, the system now has a capacity of 3,100 MW and is known as the Pacific DC Intertie.

The concept of a "super grid" dates back to the 1960s and was used to describe the emerging unification of the Great Britain grid. In the code that governs the British Grid, the Grid Code, the Supergrid is currently defined – and has been since this code was first written, in 1990 – as referring to those parts of the British electricity transmission system that are connected at voltages in excess of 200 kV (200,000 volts). British power system planners and operational staff therefore invariably speak of the Supergrid in this context; in practice the definition used captures all of the equipment owned by the National Grid company in England and Wales, and no other equipment.

What has changed during the past 40 years is the scale of energy and distances that are imagined possible in a super grid. Europe began unifying its grids in the 1950s and its largest unified grid is the synchronous grid of Continental Europe serving 24 countries. Serious work is being conducted on unification of this synchronous European grid (previously known as the UCTE grid), with the neighboring synchronous transmission grid of some CIS countries, the IPS/UPS grid. If completed, the resulting massive grid would span 13 time zones stretching from the Atlantic to the Pacific.

While such grids cover great distances, the capacity to transmit large volumes of electricity remains limited due to congestion and control issues. The SuperSmart Grid (Europe) and the Unified Smart Grid (US) specify major technological upgrades that proponents claim are necessary to assure the practical operation and promised benefits of such transcontinental mega grids.

In current usage, "super grid" has two senses – one of being a superstructure layer overlaid or super-imposed upon existing regional transmission grid or grids, and the second of having some set of superior abilities exceeding those of even the most advanced grids.

In the "overlay", or "superstructure" meaning, a super grid is a very long-distance equivalent of a wide area synchronous network capable of large-scale transmission of renewable electricity. In some conceptions, a transmission grid of HVDC transmission lines forms a layer that is distinctly separate in the way that a superhighway system is separate from the system of city streets and regional highways. In more conventional conceptions such as the proposed unification of the synchronous European grid UCTE and the IPS/UPS system of the CIS, such a mega grid is no different from typical wide area synchronous transmission systems where electricity takes an ad hoc transit route directly through local utility transmission lines or HVDC lines as required. Studies for such continental sized systems report there are scaling problems as a result of network complexity, transmission congestion, and the need for rapid diagnostic, coordination and control systems. Such studies observe that transmission capacity would need to be significantly higher than current transmission systems in order to promote unimpeded energy trading across distances unbounded by state, regional or national, or even continental borders. As a practical matter, it has become necessary to incorporate smart grid features such as wide area sensor networks (WAMS) into even modest-sized regional grids in order to avert major power outages such as the Northeast Blackout of 2003. Dynamic interactions between power generation groups are increasingly complex, and transient disturbances that cascade across neighboring utilities can be sudden, large and violent, accompanied by abrupt changes in the network topology as operators attempt to manually stabilize the network.

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