Grid connection
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The electrical power network (also known as the electrical grid) in the grandest sense consists of three distinct operations:
Generating plants are usually located near a source of water, and away from heavily populated areas. They are usually quite large in order to take advantage of the Economies of scale. The electric power which is generated is stepped up to a higher voltage -- at which it connects to the transmission network. The transmission network will move (wheel) the power long distances -- often across state lines, and sometimes across international boundaries -- until it reaches its wholesale customer (usually the company that owns the local distribution network.) Upon arrival at the substation, the power will be stepped down in voltage -- from a transmission level voltage to a distribution level voltage. As it exits the substation, it enters the distribution wiring. Finally, upon arrival at the service location, the power is stepped down again from the distribution voltage to the required service voltage(s).
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[edit] Connection to the Grid
A premises is generally said to have obtained grid connection when its service location becomes powered by a live connection to its service transformer.
A power station is generally said to have achieved grid connection when it first supplies power outside of its own boundaries. However, a town is only said to have achieved grid connection when it is connected to several redundant sources, generally involving long-distance transmission.
This redundancy is limited. A national grid is usually not a grid in any strict or mathematical sense, but simply the interconnection of facilities that provides whatever redundancy is available. The exact stage of development at which the supply structure becomes a grid is arbitrary. Similarly, the term national grid is something of an anachronism in many parts of the world, as transmission cables now frequently cross national boundaries. The terms distribution grid for local connections and transmission grid for long-distance transmissions are therefore preferred, but national grid is often still used for the overall structure.
[edit] Grid Structures
As the name implies, the topology of the grid can vary considerably from place to place. This should be expected since the grid must use the available land, and as it's said: "no two pieces of real estate are alike". In the largest of cities, the downtown distribution network does sometimes resemble a rectangular grid. It tends to follow the streets (either above ground or underground), and is usually fed from multiple substations.
Some large cities have unusual "tied ring" networks.
In all other cities and towns, the distribution network tends to be "radially fed". A substation receives its power from the transmission network, and has feeders which fan out in all directions across the countryside. These feeders carry three-phase power, and tend to follow the major streets near the substation. As the distance from the substation grows, the fanout continues as smaller laterals spread out to cover areas missed by the feeders. This tree-like structure grows outward from the substation, but for reliability reasons, usually contains at least one healthy normally-open connection to a nearby substation. This connection can be closed in in case of an emergency, so that a portion of a substation's service territory can be alternatively fed by another substation.
[edit] Modern Trends
[edit] Deregulation
The three components of a complete grid: generation, transmission, and distribution of electrical power, can all be found in most large utilities. A utility can be completely self-sufficient, but finds it advantageous to have the opportunity to buy and sell power to and from neighboring utilities. This improves their reliability, and that of their neighbors. Utilities are often awarded a "monopoly" status (at least at the distribution level) simply because it doesn't make sense to have competing utilities installing their hardware in the same location as another utility. The idea of a monopoly becomes less compelling as one considers the generation of electrical power. Wildly varying costs for the production of electricity, and the opportunity to encourage free market competition spurs many legislatures to move towards deregulation of the electric utilities (also known as "liberalization" in some parts of the world.) The idea of de-regulation usually involves the separation of the generation, transmission, and distribution operations into separate financial entities. Generation assets in particular can often be sold-off in piecemeal fashion to the highest bidders. With the aging infrastructure present at many utilities, and the pressure to de-regulate, there are numerous opportunities to re-engineer the system[1].
There are such things as a well run monopoly. There are also well run de-regulated markets. Transitioning a utility from one to the other is often fraught with peril as witnessed by the California electricity crisis.
[edit] Distributed Generation
With everything interconnected, and open competition occurring in a free market economy, it starts to make sense to allow and even encourage Distributed generation (DG). Smaller generators, usually not owned by the utility, can be brought on-line to help supply the need for power. The smaller generation facility might be a home-owner with excess power from his solar panel or wind turbine. It might be a small office with a diesel generator. These resources can be brought on-line either at the utility's behest, or by owner of the generation in an effort to sell electricity. Many small generators are allowed to sell electricity back to the grid for the same price they would pay to buy it.
[edit] Smart Grid
Numerous efforts are underway to develop a "smart grid". In the U.S., the Energy Policy Act of 2005 and Title XIII of the Energy Independence and Security Act of 2007.[2] and providing funding to encourage smart grid development. The hope is to enable utilities to better predict their needs, and in some cases involve consumers in some form of time-of-use based tariff. Funds have also been allocated to develop more robust energy control technologies.[3]
[edit] See also
- National Grid
- Electric power transmission
- Electricity distribution
- Electricity retailing
- Independent System Operator
- Load management
- Regional Transmission Organization
- Smart meter
