Editing Rectifier (section)

==== Mercury-arc ====
{{Main|Mercury-arc valve}}

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| image1   = Quecksilberdampfgleichrichter in Betrieb.JPG
| caption1 = Early [[3-phase]] industrial [[mercury vapor]] rectifier tube 
| width1   = 150
| image2   = Mercury Arc Valve, Radisson Converter Station, Gillam MB.jpg
| caption2 = 150&nbsp;kV [[mercury-arc valve]] at [[Manitoba Hydro]] power station, Radisson, Canada converted AC [[hydropower]] to DC for transmission to distant cities.
| width2   = 150
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A rectifier used in high-voltage direct current (HVDC) power transmission systems and industrial processing between about 1909 to 1975 is a ''mercury-arc rectifier'' or ''mercury-arc valve''. The device is enclosed in a bulbous glass vessel or large metal tub. One electrode, the [[cathode]], is submerged in a pool of liquid mercury at the bottom of the vessel and one or more high purity graphite electrodes, called [[anode]]s, are suspended above the pool. There may be several auxiliary electrodes to aid in starting and maintaining the arc. When an electric arc is established between the cathode pool and suspended anodes, a stream of electrons flows from the cathode to the anodes through the ionized mercury, but not the other way (in principle, this is a higher-power counterpart to [[flame rectification]], which uses the same one-way current transmission properties of the plasma naturally present in a flame).

These devices can be used at power levels of hundreds of kilowatts, and may be built to handle one to six phases of AC current. Mercury-arc rectifiers have been replaced by silicon semiconductor rectifiers and high-power [[thyristor]] circuits in the mid-1970s. The most powerful mercury-arc rectifiers ever built were installed in the [[Manitoba Hydro]] [[Nelson River Bipole]] HVDC project, with a combined rating of more than 1 GW and 450 kV.<ref>Pictures of a mercury-arc rectifier in operation can be seen here: [http://www.subbrit.org.uk/sb-sites/sites/b/belsize_park_deep_shelter/index14.shtml Belsize Park deep shelter rectifier 1], [http://www.subbrit.org.uk/sb-sites/sites/b/belsize_park_deep_shelter/index13.shtml Belsize Park deep shelter rectifier 2]</ref><ref name=sood1>{{cite book
|url=https://www.amazon.com/gp/reader/1402078900/ref=sib_fs_top?ie=UTF8&p=S00T&checkSum=kIuBlcbI0cpOJz1UiVfSKdIqFhPcDOXQ98WG3SabLpA%3D#reader-link
| title= HVDC and FACTS Controllers: Applications of Static Converters in Power Systems
| last=Sood
| first=Vijay K
| page=1
| publisher=[[Springer-Verlag]]
| isbn=978-1-4020-7890-3
| quote= The first 25 years of HVDC transmission were sustained by converters having mercury arc valves till the mid-1970s. The next 25 years till the year 2000 were sustained by line-commutated converters using thyristor valves. It is predicted that the next 25 years will be dominated by force-commutated converters [4]. Initially, this new force-commutated era has commenced with Capacitor Commutated Converters (CCC) eventually to be replaced by self-commutated converters due to the economic availability of high-power switching devices with their superior characteristics.| date= 31 May 2004
}}</ref>
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