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Electric power transmission is the second process in the delivery of electricity to consumers. Electricity is generated by power plants and is then sold as a commodity to end consumers by retailers. The electric power transmission and electricity distribution networks allow the delivery of the generated electricity to consumers. The rapid industrialization in the 20th century made electric power transmission lines and grids a critical part of the economic infrastructure in most industrialized nations.
The transmission grid allows large generation facilities such as hydroelectric dams, fossil fuel plants, nuclear power plants, etc. run by large public and private utility organizations to produce large quantities of energy and then deliver it to distribution networks for delivery to retail customers for consumption.
Electricity is usually sent over long distance through a combination of overhead power transmission lines (such as those in the photo on the right) or buried cables.
The first large scale hydroelectric generators in the USA (engineered and installed under the technical oversight of Nikola Tesla) were installed at Niagara Falls and provided electricity to Buffalo, New York via power transmission lines.
A transmission grid is made up of power stations, substations, and transmission circuits. Power is usually transmitted as a 3-phase alternating currentAn alternating current AC is an electrical current, where the magnitude of the current varies in a cyclical form, as opposed to direct current, where the polarity of the current stays constant. The usual waveform of an AC circuit is generally that of a pe (AC). At the generating plants the power is produced at a relatively low voltage of 10-15 kV, then stepped up by the power station transformerThe word Transformer can also mean: The Transformers toys, and the related comics and animated television series which have run from the 1980s onwards. A glam rock album by Lou Reed, named Transformer . Transformers ''Typical electrical configurations See to a high voltage (220 - 400 kV) alternating current for transmission over longer distances to grid exit points ( substations).
It is necessary to transmit the electricity at high voltage to reduce the percentage of power lost. The higher the voltage the lower the current that flows, which reduces the size of cable needed and the amount of energy wasted. Long distance transmission is typically at voltages of 100 kV and higher. Transmission and distribution losses in the USA were estimated at 7.2% in 20032003 is a common year starting on Wednesday (link will take you to calendar), and also: The International Year of Freshwater The European Disability Year Summary Perhaps the defining global event of the year 2003 was the Invasion of Iraq launched by the U [1], and in the UK at 7.4% in 19981998 was a common year starting on Thursday (see link for calendar), and was designated the International Year of the Ocean''. Events January January 1998 A massive ice storm, caused by El Nino, strikes New England, southern Ontario and Quebec, resulting [2].
When power is required to be transmitted over very long distances, it becomes more efficient (and hence economical) to transmit using direct current ( HVDC) instead of alternating current. This is because smaller insulators are required for a DC line than an AC line carrying a given amount of power. Also, at high AC voltages significant amounts of power are lost due to the capacitanceCapacitance is the ability of a capacitor to store potential difference or voltage for a given amount of stored charge. The SI unit of capacitance is the farad. where C is the capacitance, measured in farads Q is the charge, measured in coulombs V is the between phase lines or, in the case of buried cables, between a phase line and the soil or water in which the cable is buried. HVDC is used for very high quantities of power over very long distances, for undersea cables over ten kilometers or so (as undersea cables have a very large capacitance), or between asynchronous grids. Since the power flow across a HVDC link is directly controllable, HVDC links are sometimes used within a grid to stabilize the grid against control problems with the AC power flow.
Current can flow in an AC line even when the voltage is zero. Typically, this flow is due to inductance at the load or within the AC distribution line itself, and is called a reactive flow. Reactive flows transmit no power from the generator to the load, but they burn power within the grid. The fraction of total power which is resistive (as opposed to reactive) power is the power factor. Utilities add capacitor banks throughout the system to improve the power factor, in order to reduce the associated real power losses.
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