Electric power transmission,
A process in the delivery of electricity consumers, is the bulk transfer of electrical power. A power transmission network connects power plants to multiple substractions near a populated area. The wiring from substations to customers is referred to as electricity distributions following the historic business model separating the wholesale electricity transmission business from distributors who deliver the electricity to the homes. Electric power transmission allows distant energy sources (such as hydroelectric power plants) to be connected to consumers in population centers, and may allow exploitation of low-grade fuel resources such as coal that would otherwise be too costly to transport to generating facilities.Usually transmission lines use three phase AC current .Single Phase AC current is sometimes used in a railway electrification. High voltage direct current systems are used for long distance transmission, or some undersea cables, or for connecting two different ac networks.
Electricity is transmitted at high voltages (110 kV or above) to reduce the energy lost in transmission. Power is usually transmitted as alternating current through overhead power lines. Underground power transmission is used only in densely populated areas because of its higher cost of installation and maintenance when compared with overhead wires,and the difficulty of voltage control on long cables.A power transmission network is referred to as a "grid". Multiple redundant lines between points on the network are provided so that power can be routed from any power plant to any load center, through a variety of routes, based on the economics of the transmission path and the cost of power. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line, which, due to system stability considerations, may be less than the physical or thermal limit of the line. Deregulation of electricity companies in many countries has led to renewed interest in reliable economic design of transmission networks. However, in some places the gaming of a deregulated energy system has led to disaster, such as that which occurred during the
Overhead transmission:Overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for overhead transmission but aluminum is lower in weight for equivalent performance, and much lower in cost. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits.
Conductor sizes in overhead transmission work range in size from American wire gauge (about 12 square millimeters) to 1,590,000 circular mils area (about 750 square millimeters), with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect that causes most of the current to flow close to the surface of the wire.
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