View source for Current limiting reactor

In [[electrical engineering]], '''current limiting reactors''' can reduce [[short-circuit]] [[Electric current|current]]s, which result from plant expansions and power source additions, to levels that can be adequately handled by existing distribution equipment.<ref name="Source 1">{{cite web|last=Simpson|first=James|title=The how and why of current-limiting reactors|publisher=EC&M Electrical Construction & Maintenance|accessdate=}}</ref>
They can also be used in high voltage electric power transmission grids for a similar purpose. In the control of electric motors, current limiting reactors can be used to restrict starting current or as part of a speed control system.
[[File:NoxonReactor.jpg|thumb|right| A set of air-core reactors installed outdoors at a substation. Similar reactors are used for current limiting at transmission and distribution voltage levels.]]

== History ==
Current limiting reactors, once called current limiting [[Electrical reactance|reactance]] coils, were first presented in 1915.<ref name="Source 4">{{cite conference |title=The Use of Current-Limiting Reactors |first1=Walter Melville |last1=Dann |first2=H. H. |last2=Rudd |url=http://babel.hathitrust.org/cgi/pt?id=nnc1.cu55816380;page=root;view=image;size=100;seq=5;num=1 |conference=Meeting of the Society of Mechanical, Electrical, and Steam Engineers |location=Boody House, [[Toledo, Ohio]] |date=June 17–18, 1915 |accessdate=18 September 2012}}</ref>
The inventor of the current limiting reactance coil was Vern E. Alden who filed the patent on November 20, 1917 with an issue date of September 11, 1923. The original assignee was [[Westinghouse Electric & Manufacturing Company]].<ref name="Source 5">{{cite patent |inventor-last=Alden |inventor-first=Vern |country=US |number=1467771 |title=Current Limiting Reactance Coil |assign=Westinghouse Electric and Manufacturing Company |gdate=September 11, 1923}}</ref>

== Operation ==
A current limiting reactor is used when the [[prospective short-circuit current]] in a distribution or transmission system is calculated to exceed the [[interrupting rating]] of the associated [[switchgear]].  The inductive reactance is chosen to be low enough for an acceptable voltage drop during normal operation, but high enough to restrict a short circuit to the rating of the switchgear. 
The amount of protection that a current limiting reactor offers depends upon the percentage increase in impedance that it provides for the system.<ref name="Source 2">{{cite web|title=Current Limiting Reactors: Technical Overview and Measurement Procedures|url=http://www.nwl.com/files/file/Tech%20Bulletins/222.pdf|publisher=NWL|accessdate=17 September 2012|url-status=dead|archiveurl=https://web.archive.org/web/20140303231851/http://www.nwl.com/files/file/Tech%20Bulletins/222.pdf|archivedate=3 March 2014}}</ref>

[[File:Current Limiting Reactor.jpg|thumb|Current limiting reactor]]

The main motive of using current limiting reactors is to reduce short-circuit currents so that circuit breakers with lower short circuit breaking capacity can be used. They can also be used to protect other system components from high current levels and to limit the inrush current when starting a large motor.<ref name="Source 3">{{cite web|title=Quality Power|url=http://www.qualitypower.co.in/current-reactors.php|accessdate=17 September 2012|archive-date=10 March 2019|archive-url=https://web.archive.org/web/20190310233907/http://www.qualitypower.co.in/current-reactors.php|url-status=dead}}</ref>

==Construction==
It is desirable that the reactor does not go into magnetic saturation during a short circuit, so generally an air-core [[electromagnetic coil|coil]] is used. At low and medium voltages, air-insulated coils are practical; for high transmission voltages, the coils may be immersed in [[transformer oil]]. 
Installation of air-core coils requires consideration of the magnetic field produced by the coils, which may induce current in large nearby metal objects. This may result in objectionable temperature rise and waste of energy.<ref>"Electrical Transmission and Distribution Reference Book", Westinghouse Electr Corporation, Pittsburgh PA, 1950 pp. 133-135</ref>

==Line reactor==
A '''line reactor''' is an inductor wired between a power source and a load.  In addition to the current limiting function, the device serves to filter out spikes of current <ref>http://www.myronzucker.com/linereactorpg1.html What is a Line Reactor?</ref>  and may also reduce injection of harmonic currents into the power supply.  The most common type is designed for [[three-phase electric power]], in which three isolated inductors are each wired in series with one of the three line phases.<ref>{{cite web |url=http://www.cosphi.com/line-load-reactor-applications.html |title=Cos Phi Inc. - Line/Load Reactor Applications |accessdate=2014-04-01 |url-status=dead |archiveurl=https://web.archive.org/web/20121228061844/http://www.cosphi.com/line-load-reactor-applications.html |archivedate=2012-12-28 }} Line reactor configurations</ref> Line reactors are generally installed in motor driven equipment to limit starting current, and may be used to protect [[Variable-frequency drive]]s and motors.:<ref>{{cite web |url=http://ecmweb.com/mag/electric_line_reactors_vfds/ |title=Line Reactors and VFDs |website=ecmweb.com |url-status=dead |archive-url=https://web.archive.org/web/20041020075825/http://www.ecmweb.com/mag/electric_line_reactors_vfds/ |archive-date=2004-10-20}} </ref>)

==See also==
*[[Electrical ballast]]

== References ==
{{reflist}}

[[Category:Electrical engineering]]
[[Category:Electric power transmission]]
[[Category:American inventions]]
[[Category:Over-current protection devices]]