Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.
Power is defined formally as units of energy per unit time. In SI units:
Since the development of technology, transmission and storage systems have been of immense interest to technologists and technology users.
With the widespread establishment of power grids, power transmission is usually associated most with electric power transmission. Alternating current is normally preferred as its voltage may be easily stepped up by a transformer in order to minimize resistive loss in the conductors used to transmit power over great distances; another set of transformers is required to step it back down to safer or more usable voltage levels at destination.
Power transmission is usually performed with overhead lines as this is the most economical way to do so. Underground transmission by high voltage cables is chosen in crowded urban areas and in HVDC submarine connections.
Power might also be transmitted by changing electromagnetic fields or by radio waves; microwave energy may be carried efficiently over short distances by a waveguide.
Electrical power transmission has replaced mechanical power transmission in all but the very shortest distances. From the 16th century through the industrial revolution to the end of the 19th century mechanical power transmission was the norm. The oldest long-distance power transmission technology involved systems of push-rods (stängenkunst or feldstängen) connecting waterwheels to distant mine-drainage and brine-well pumps. A surviving example from 1780 exists at Bad Kösen that transmits power approximately 200 meters from a waterwheel to a salt well, and from there, an additional 150 meters to a brine evaporator. This technology survived into the 21st century in a handful of oilfields in the US, transmitting power from a central pumping engine to the numerous pump-jacks in the oil field.
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