Editing Electric power transmission (section)

== Specialized transmission ==

=== Grids for railways ===
{{Main|Traction power network}}

In some countries where [[electric locomotive]]s or [[electric multiple unit]]s run on low frequency AC power, separate single phase [[traction power network]]s are operated by the railways. Prime examples are countries such as Austria, Germany and Switzerland that utilize AC technology based on 16&nbsp;<sup>2</sup>''/''<sub>3</sub>&nbsp;Hz. Norway and Sweden also use this frequency but use conversion from the 50&nbsp;Hz public supply; Sweden has a 16&nbsp;<sup>2</sup>''/''<sub>3</sub>&nbsp;Hz traction grid but only for part of the system.

=== Superconducting cables ===
[[High-temperature superconductor]]s (HTS) promise to revolutionize power distribution by providing lossless transmission. The development of superconductors with transition temperatures higher than the boiling point of [[liquid nitrogen]] has made the concept of superconducting power lines commercially feasible, at least for high-load applications.<ref>{{cite journal |doi=10.1109/77.920339 |author=Jacob Oestergaard |journal=IEEE Transactions on Applied Superconductivity |title=Energy losses of superconducting power transmission cables in the grid |year=2001 |volume=11 |issue=1 |page=2375|bibcode=2001ITAS...11.2375O |s2cid=55086502 |display-authors=etal|url=http://orbit.dtu.dk/files/4280307/%C3%B8stergaard.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://orbit.dtu.dk/files/4280307/%C3%B8stergaard.pdf |archive-date=2022-10-09 |url-status=live }}</ref> It has been estimated that waste would be halved using this method, since the necessary refrigeration equipment would consume about half the power saved by the elimination of resistive losses. Companies such as [[Consolidated Edison]] and [[American Superconductor]] began commercial production of such systems in 2007.<ref>{{cite web |last=((New Scientist and Reuters)) |date=22 May 2007 |title=Superconducting power line to shore up New York grid |url=https://www.newscientist.com/article/dn11907-superconducting-power-line-to-shore-up-new-york-grid/ |website=New Scientist}}</ref>

Superconducting cables are particularly suited to high load density areas such as the business district of large cities, where purchase of an [[easement]] for cables is costly.<ref>{{cite web |url=http://www.futureenergies.com/modules.php?name=News&file=article&sid=237 |title=Superconducting cables will be used to supply electricity to consumers |access-date=June 12, 2014 |archive-url=https://web.archive.org/web/20140714161200/http://www.futureenergies.com/modules.php?name=News&file=article&sid=237 |archive-date=July 14, 2014 |url-status=dead }}</ref>

{| class="wikitable sortable"
|+HTS transmission lines<ref>{{cite web |url=https://spectrum.ieee.org/biomedical/imaging/superconductivitys-first-century/3 |title=Superconductivity's First Century |access-date=August 9, 2012 |archive-url=https://web.archive.org/web/20120812011121/https://spectrum.ieee.org/biomedical/imaging/superconductivitys-first-century/3 |archive-date=August 12, 2012 |url-status=dead }}</ref>
|-
! Location !! Length (km) !! Voltage (kV) !! Capacity (GW) !! Date
|-
|Carrollton, Georgia || || || || 2000
|-
|align=left|Albany, New York<ref>{{cite web|url=http://www.superpower-inc.com/content/hts-transmission-cable|title=HTS Transmission Cable|website=www.superpower-inc.com}}</ref>|| 0.35 || 34.5 || 0.048 ||2006
|-
|[[Holbrook Superconductor Project|Holbrook, Long Island]]<ref>{{cite web|url=http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/hightempsuperconductors/|archive-url=https://web.archive.org/web/20120403014711/http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/hightempsuperconductors/|url-status=dead|archive-date=April 3, 2012|title=IBM100 - High-Temperature Superconductors|date=August 10, 2017|website=www-03.ibm.com}}</ref>|| 0.6 || 138 || 0.574 || 2008
|-
|align=left|[[Tres Amigas SuperStation|Tres Amigas]]|| || || 5 || Proposed 2013
|-
|align=left|Manhattan: Project Hydra|| || || || Proposed 2014
|-
|align=left|Essen, Germany<ref>{{cite web|url=https://www.powermag.com/high-temperature-superconductor-technology-stepped-up/|title=High-Temperature Superconductor Technology Stepped Up|first=03/01/2012 &#124; Sonal|last=Patel|date=March 1, 2012|website=POWER Magazine}}</ref><ref>{{cite web|url=https://phys.org/news/2014-05-longest-superconducting-cable-worldwide.html|title=Operation of longest superconducting cable worldwide started|website=phys.org}}</ref>|| 1 || 10 || 0.04 || 2014
|}

=== Single-wire earth return ===
{{Main|Single-wire earth return}}{{Unreferenced section|date=November 2022}}
Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line for supplying single-phase electrical power to remote areas at low cost. It is principally used for [[rural electrification]], but also finds use for larger isolated loads such as water pumps. Single-wire earth return is also used for HVDC over submarine power cables.

=== Wireless power transmission ===
{{Main|Wireless power transfer}}{{Unreferenced section|date=November 2022}}
Both [[Nikola Tesla]] and [[Hidetsugu Yagi]] attempted to devise systems for large scale wireless power transmission in the late 1800s and early 1900s, without commercial success.

In November 2009, LaserMotive won the NASA 2009 Power Beaming Challenge by powering a cable climber 1&nbsp;km vertically using a ground-based laser transmitter. The system produced up to 1&nbsp;kW of power at the receiver end. In August 2010, NASA contracted with private companies to pursue the design of laser power beaming systems to power low earth orbit satellites and to launch rockets using laser power beams.

Wireless power transmission has been studied for transmission of power from [[solar power satellite]]s to the earth. A high power array of [[microwave]] or laser transmitters would beam power to a [[rectenna]]. Major engineering and economic challenges face any solar power satellite project.