Editing Power transmission

{{Short description|Movement of energy from its source to where it can be applied}}
'''Power transmission''' is the movement of [[energy]] from its place of generation to a location where it is applied to perform useful [[Mechanical work|work]].

[[Power (physics)|Power]] is defined formally as units of [[energy]] per unit [[time]]. In [[SI]] units:

:<math>\text{watt} = \frac{\text{joule}}{\text{second}} = \frac{\text{newton}\times\text{meter}}{\text{second}}</math>

Since the development of [[technology]], [[Transmission (mechanics)|transmission]] and storage systems have been of immense interest to technologists and [[technology]] users.

== Electrical power ==
{{Main|Electric power transmission}}
[[File:Electric transmission lines.jpg|thumb|Electric power transmission with overhead line.]]

With the widespread establishment of [[electrical grid]]s, 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 [[electrical resistance|resistive]] loss in the [[Conductor (material)|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.

[[File:HV Cable.jpg|thumb|left|Electric power transmission with underground cable. Here (1) is the conductor for heavy currents and (3) the insulation for high voltages. {{Further|high-voltage cable}}]]

Power transmission is usually performed with [[Overhead power line|overhead line]]s as this is the most economical way to do so. Underground transmission by [[high-voltage cable]]s is chosen in crowded urban areas and in [[High-voltage direct current|high-voltage direct-current]] (HVDC) submarine connections.

Power might also be transmitted by changing [[electromagnetic field]]s or by [[radio waves]]; [[microwave]] energy may be carried efficiently over short distances by a [[waveguide]] or in free space via [[wireless power transfer]].

== Mechanical power ==
[[Image:Gears large.jpg|thumb|Mechanical power transmission using gears]]
{{Main|Transmission (mechanics)}}

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 or [[Flatrod system|jerker lines]] (''stängenkunst'' or ''feldstängen'') connecting waterwheels to distant mine-drainage and brine-well pumps.<ref>Dianne Newell, [https://www.jstor.org/pss/124651 Technological Innovation and Persistence in the Ontario Oilfields: Some Evidence from Industrial Archaeology], ''World Archaeology 15,'' 2, Industrial Archaeology (Oct., 1983), pp. 184-195</ref> 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.<ref>Michael Pfefferkorn, [https://www.untertage.com/publikationen/18-thueringen/56-der-solschacht-von-bad-koesen-und-sein-feldgestaenge.html Der Solschacht von Bad Kösen und sein Feldgestänge], Grubenarchäologischen Gesellschaft, 2004.</ref>  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.<ref>Keith Kinney, [https://web.archive.org/web/20110711163322/http://www.herculesengines.com/FlatRock/ The last two oil leases in Illinois using a central power and rod lines -- Powered by 35 H.P. Superior Oil Field Engines, Flat Rock, Illinois], 2003</ref>

Mechanical power may be transmitted directly using a solid structure such as a [[driveshaft]]; [[Transmission (mechanics)|transmission]] [[gear]]s can adjust the amount of [[torque]] or [[force]] vs. [[speed]] in much the same way an electrical transformer adjusts [[voltage]] vs [[Electric current|current]].  Factories were fitted with overhead [[line shaft]]s providing [[rotary power]]. Short line-shaft systems were described by [[Georg Agricola|Agricola]], connecting a waterwheel to numerous ore-processing machines.<ref>Georgius Agricola, [[De re metallica]], 1556. See {{cite web|url=http://www.btinternet.com/~stephen.henley/agricola/book8/book8-22.jpg|title=book 8 figure 22|archive-url=https://archive.today/20120630225125/http://www.btinternet.com/~stephen.henley/agricola/book8/book8-22.jpg|archive-date=2012-06-30}}</ref>  While the machines described by Agricola used geared connections from the shafts to the machinery, by the 19th century, [[belt (mechanical)|drivebelts]] would become the norm for linking individual machines to the line shafts. One mid 19th century factory had 1,948 feet of line shafting with 541 pulleys.<ref>[https://books.google.com/books?id=I-0RAAAAYAAJ&pg=PA164 The United States Magazine of Science, Art, Manufactures, Agriculture, Commerce and Trade], Vol. 2, 1856, page 164.</ref>

[[Hydraulic]] systems use liquid under pressure to transmit power; [[canal]]s and [[hydroelectric]] [[power generation]] facilities harness natural water power to lift [[ship]]s or generate electricity. Pumping water or pushing mass uphill with ([[windmill]] pumps) is one possible means of [[energy storage]]. [[London]] had a [[hydraulic network]] powered by five [[pumping station]]s operated by the [[London Hydraulic Power Company]], with a total effect of 5 MW.

[[Pneumatic]] systems use gasses under pressure to transmit power; [[Pneumatics|compressed air]] is commonly used to operate [[pneumatic]] [[tool]]s in [[factories]] and [[repair]] garages. A pneumatic wrench (for instance) is used to remove and install automotive tires far more quickly than could be done with standard manual hand tools.  A pneumatic system was proposed by proponents of [[Thomas Edison|Edison's]] [[direct current]] as the basis of the power grid. Compressed air generated at [[Niagara Falls]] would drive far away generators of DC power. The [[war of the currents]] ended with [[alternating current]] (AC) as the only means of long distance power transmission.

== Thermal power ==
Thermal power can be transported in pipelines containing a high [[heat capacity]] fluid such as oil or water as used in [[district heating]] systems, or by physically transporting material items, such as bottle cars, or in the ice trade.

==Chemicals and fuels==
While not technically power transmission, energy is commonly transported by shipping [[chemical]] or [[nuclear power|nuclear]] [[fuel]]s. Possible artificial fuels include [[radioactive isotope]]s, [[Methanol|wood alcohol]], [[Ethanol|grain alcohol]], [[methane]], [[synthetic gas]], [[hydrogen]] gas (H<sub>2</sub>), [[cryogenic]] [[gas]], and [[liquefied natural gas]] (LNG).

==See also==
{{Portal|energy}}

*[[Distributed generation]]
*[[List of energy storage power plants]]

==External links==
* {{cite EB1911 |wstitle=Power Transmission |volume=22 |pages=224–238}} : [[s:1911 Encyclopædia Britannica/Power Transmission/Mechanical|Mechanical]], [[s:1911 Encyclopædia Britannica/Power Transmission/Hydraulic|Hydraulic]],  [[s:1911 Encyclopædia Britannica/Power Transmission/Pneumatic|Pneumatic]], [[s:1911 Encyclopædia Britannica/Power Transmission/Electrical|Electrical]].
==References==
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[[Category:Electric power transmission]]