Editing Electric power transmission (section)

{{Short description|Bulk movement of electrical energy}}
{{other uses|Electric transmission (disambiguation)}}
{{redirect|Power lines|power lines in general|Overhead power line}}
{{Use mdy dates|date=April 2014}}
{{Multiple issues|{{Globalize|date=August 2022}}
{{Update|date=August 2022}}
{{more footnotes|date=August 2022}}}}
[[File:500kV 3-Phase Transmission Lines.png|thumb|Five-hundred kilovolt (500 kV) [[Three-phase electric power]] Transmission Lines at [[Grand Coulee Dam]]. Four circuits are shown. Two additional circuits are obscured by trees on the far right. The entire 6809&nbsp;MW<ref name="GCPP">{{cite web|title=Grand Coulee Powerplant|url=http://www.usbr.gov/projects/Powerplant.jsp?fac_Name=Grand%20Coulee%20Powerplant|publisher=U.S. Bureau of Reclamation|access-date=March 11, 2015|url-status=dead|archive-url=https://web.archive.org/web/20140429162702/http://www.usbr.gov/projects/Powerplant.jsp?fac_Name=Grand%20Coulee%20Powerplant|archive-date=April 29, 2014}}</ref> nameplate generation capacity of the dam is accommodated by these six circuits.]]
'''Electric power transmission''' is the bulk movement of [[electrical energy]] from a [[power generation|generating]] site, such as a [[power plant]], to an [[electrical substation]]. The interconnected lines that facilitate this movement form a ''transmission network''. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as [[electric power distribution]]. The combined transmission and distribution network is part of [[electricity delivery]], known as the [[electrical grid]].

Efficient long-distance transmission of electric power requires high [[voltages]]. This reduces the losses produced by strong [[Electric current|currents]]. Transmission lines use either [[alternating current]] (AC) or [[direct current]] (DC). The voltage level is changed with [[transformer]]s. The voltage is stepped up for transmission, then reduced for local distribution.

A [[wide area synchronous grid]], known as an ''interconnection'' in North America, directly connects generators delivering AC power with the same relative ''frequency'' to many consumers. North America has four major interconnections: [[Western Interconnection|Western]], [[Eastern Interconnection|Eastern]], [[Quebec Interconnection|Quebec]] and [[Texas Interconnection|Texas]]. [[Synchronous grid of Continental Europe|One grid connects most of continental Europe]].

Historically, transmission and distribution lines were often owned by the same company, but starting in the 1990s, many countries [[Electricity liberalization|liberalized]] the regulation of the [[electricity market]] in ways that led to separate companies handling transmission and distribution.<ref name=femp01>{{cite web|url=https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-13906.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-13906.pdf |archive-date=2022-10-09 |url-status=live|title=A Primer on Electric Utilities, Deregulation, and Restructuring of U.S. Electricity Markets|publisher=[[United States Department of Energy]] [[Federal Energy Management Program]] (FEMP)|date=May 2002|access-date=October 30, 2018}}</ref>