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{{Expand French|Appareillage électrique à haute tension|date=March 2022|topic=sci}}
[[Image:Switchgear HV.jpg|thumb|800 kV high-voltage switchgear]]
'''High voltage switchgear''' is any [[switchgear]] used to connect or disconnect a part of a [[electric power transmission|high-voltage power system]]. This equipment is essential for the protection and safe operation, without interruption, of a high voltage power system, and is important because it is directly linked to the quality of the electricity supply.

The term "high voltage" covers the former medium voltage (MV) and the former high voltage (HV), and therefore refers to equipment with a rated voltage of over 1,000 V in the case of [[alternating current]], and over 1,500 V in the case of [[direct current]]. The industrial applications of high voltage circuit breakers are for the moment limited to alternating current because they are more economical, there are however high voltage disconnectors for direct current connections.

High voltage switchgear was invented at the end of the [[19th century]] for operating [[Electric motor|motors]] and others electric machines.<ref>[http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=GB189320069&F=0&QPN=GB189320069 British Pattern GB 20069 ''Improvements in Apparatus for Controlling the Application or Use of Electric Currents of High Tension and Great Quantity'' in 1893], on espacenet.com</ref> The technology has been improved over time and can be used with voltages up to 1,100 kV.<ref name="1100kV">Lin Jiming et al., ''Transient characteristics of 1 100 kV circuit-breakers'', ''International Symposium on International Standards for Ultra High Voltage'', Beijing, Juillet 2007.</ref>

==Classification==

=== Functional Classification ===

====Disconnectors and earthing switches====

[[Disconnector]]s and earthing switches are safety devices used to open or to close a [[electronic circuit|circuit]] when there is no [[Electric current|current]] through them. They are used to isolate a part of a circuit, a machine, a part of an [[overhead power line|overhead line]] or an [[Electrical cable|underground line]] so that maintenance can be safely conducted.

The opening of the line [[isolator switch|isolator]] or [[busbar]] section isolator is necessary for safety, but not sufficient. [[Ground (electricity)|Grounding]] must be conducted at both the upstream and downstream sections of the device under maintenance. This is accomplished by earthing switches.

In principle, disconnecting switches do not have to interrupt currents, as they are designed for use on de-energized circuits. In practice, some are capable of interrupting currents (as much as 1,600 [[ampere]] under 300 V but only if current is drawn via a same circuit half breaker bypass system), and some earthing switches must interrupt induced currents which are generated in a non-current-carrying line by [[inductance|inductive]] and [[capacitance|capacitive]] coupling with nearby lines (up to 160 A under 20 kV).<ref>[http://domino.iec.ch/preview/info_iec62271-102{ed1.0}b.pdf ''IEC 62271-102 for A.C. disconnectors and earthing switches'']</ref>

====High-current switching mechanism====

High-current switching mechanisms are used for energized circuits carrying a normal load. Some can be used as a disconnecting switch.

However, if they can create a short-circuit current, they can not interrupt it.<ref>[http://domino.iec.ch/preview/info_iec60265-1{ed3.0}b.pdf ''Norme CEI 60265-1  Interrupteurs pour tension assignée supérieure à 1 kV et inférieure à 52 kV'']</ref><ref>[http://domino.iec.ch/preview/info_iec60265-2{ed1.0}b.img.pdf ''Norme CEI 60265-2 Interrupteurs pour tension assignée supérieure à 52 kV'']</ref>

====Contactor====

Contactors are similar in function to high-current switching mechanisms, but can be used at higher rates. They have a high electrical endurance and a high mechanical endurance.<ref>[http://domino.iec.ch/preview/info_iec60470{ed2.0}b.pdf Norme CEI 60470 ''Contacteurs pour courant alternatif haute tension et démarreurs de moteurs à contacteurs'']</ref>

====Fuses====

A [[fuse (electrical)|fuse]] can automatically interrupt a circuit with an overcurrent flowing in it for a fixed time. This is accomplished by the fusion of an [[electrical conductor]] which is graded.

Fuses are mainly used to protect against [[short circuit]]s. They limit the peak value of the fault current.

In [[three-phase electric power]], they only eliminate the [[polyphase system|phases]] where the fault current is flowing, which can pose a risk for both the malfunctioning devices and the people. To alleviate this problem, fuses can be used in conjunction with high-current switches or contactors.

Like contactors, high-voltage fuses are used only in the band 30 kV to 100 kV.{{Citation needed|date=September 2008}}

====Circuit Breaker====

A high voltage [[circuit breaker]] is capable of connecting, carrying and disconnecting [[electric current|currents]] under the rated [[voltage]] (the maximal voltage of the [[electric power transmission|power system]] which it is protecting).

Under normal operational conditions, circuit breakers can be used to (dis)connect a line. Circuit breakers can also be used to interrupt current when anomalies are detected, such as a short-circuit.

Circuit breakers are essential elements of high-voltage power systems because they are the only means to safely interrupt a [[short circuit|short circuit current]]. The international standard [[List of IEC standards|IEC 62271-100]] defines the demands linked to the characteristics of a high voltage circuit breaker.<ref>[http://domino.iec.ch/preview/info_iec62271-100{ed1.2}b.pdf ''Norme CEI 62271-100 Disjoncteurs à haute tension'']</ref>

The circuit breaker can be equipped with electronic devices in order to know at any moment their states, such as wear or gas pressure, and to detect faults from characteristic derivatives. It can also permit planned maintenance operations and to avoid failures.<ref>E.Thuries, G.Ebersohl, J.P.Dupraz, O.Chetay, J.P.Montcorgé, ''Introduction de l'électronique numérique dans les auxiliaires de l'appareillage et amélioration de la fiabilité'', 1994, CIGRE session 1994, rapport 23/13-09</ref><ref name="Disjoncteur SF6">Denis Dufournet, ''Disjoncteurs SF<sub>6</sub> - Évolution de 1959 à 1994, 1994'', ''Revue générale de l'électricité'' n° 5</ref>

To operate on long lines, circuit breakers are equipped with a closing [[resistor]] to limit [[overvoltage]]s.<ref>D.E. Heldman, I.B. Johnson, C.H. Titus, D.D. Wilson, ''Switching of Extra-High-Voltage Circuits, Surge reduction with circuit-breaker resistors'', 1964, ''[[IEEE]] Transactions on Power Apparatus and Systems'', Vol. 83 (1964-12)</ref><ref>Eugène Maury, ''Problèmes apparaissant aux tensions les plus élevées lors de la manœuvre des disjoncteurs'', 1964, CIGRE session 1964</ref>

They can be equipped with devices to synchronize closing and/or opening, to limit the overvoltages and the inrush currents from the lines, the unloaded [[transformer]]s, the shunt reactances and the [[capacitor]] banks.<ref>Eugène Maury, ''La fermeture synchronisée des disjoncteurs 525 kV et 765 kV, moyen de réduire les surtensions de manœuvre sur lignes à vide'', 1966, CIGRE session 1966.</ref><ref>Groupe de travail CIGRE 13.07, ''Controlled switching of HV AC circuit breakers'', 1999, ''Electra'' N° 183</ref>

Some devices are designed to have the characteristics of the circuit breaker and the disconnector,<ref>[http://webstore.iec.ch/preview/info_iec62271-108%7Bed1.0%7Db.pdf ''Norme CEI 62271-108 Disjoncteur-sectionneurs'']</ref> but their use is not widespread.

== See also ==
* [[Switchgear]]
* [[High voltage|High-voltage]]

==References==

{{Reflist}}

== External links ==
*[http://www.ewh.ieee.org/soc/pes/switchgear/ ''IEEE Switchgear Committee''], on ewh.ieee.org

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[[Category:Electric power systems components]]
[[Category:Electric power infrastructure]]