The Animikie Group is a geologic group composed of sedimentary and metasedimentary rock, having been originally deposited between 2,500 and 1,800 million years ago within the Animikie Basin. This group of formations is geographically divided into the Gunflint Range, the Mesabi and Vermilion ranges, and the Cuyuna Range. On the map, the Animikie Group is the dark gray northeast-trending belt which ranges from south-central Minnesota, U.S., up to Thunder Bay, Ontario, Canada. The Gunflint Iron Range is the linear black formation labeled G, the Mesabi Iron Range is the jagged black linear formation labeled F, and Cuyuna Iron Range is the two black spots labeled E. The gabbro of the Duluth Complex, intruded during the formation of the Midcontinent Rift, separates the Mesabi and Gunflint iron ranges; it is shown by the speckled area wrapping around the western end of Lake Superior.
Banded-iron formations are iron formations which formed about 2,000 million years ago and were first described in the Lake Superior region. Sediments associated with the last stage of the Great Lakes tectonic zone contain banded-iron formations. These sediments were deposited for two hundred million years and extend intermittently along roughly the same trend as the Great Lakes tectonic zone, from Minnesota into eastern Ontario, Canada, and through upper Wisconsin and Michigan. They are characterized by bands of iron compounds and chert. Enough oxygen had accumulated in seawater so that dissolved iron was oxidized; iron reacts with oxygen to form compounds that precipitate out – including hematite, limonite and siderite. These iron compounds precipitated from the seawater in varying proportions with chert, producing banded-iron formations. These iron formations are abundant in the Lake Superior region. The Sudbury Impact event occurred 1,850 million years ago; it is theorized that this caused the end of the banded-iron deposits. The results of the impact affected concentrations of dissolved oxygen in the sea; the accumulation of banded-iron formations suddenly ended   million years ago.
The Gunflint Range consists of a basal conglomerate, then the Gunflint Iron formation and the Gunflint Chert with the Rove Formation deposited on top. The Mesabi Range consists of the basal Pokegama Quartzite layer, then the Biwabik Iron Formation with the Virginia Formation deposited on top. The Vermilion Range consists of the basal Ely Greenstone, then the Soudan Iron formation with various granites on top. The Cuyuna Range consists of the basal North Range group, then the Trommald Formation with the Thomson Formation deposited on top.
Age, location and size
The Animikie Group sediments were deposited between 2,500 and 1,800 million years ago,[1]:4 in the Animikie Basin.[2] Deposition of sediments began after the Algoman orogeny and continued through the Great Lakes tectonic zone rupture from 2,200 to 1,850 million years ago.
The Animikie Group formations are in east-central and northeastern Minnesota, and the Thunder Bay District of Northern Ontario; they are geographically divided into the Gunflint Range, the Mesabi and Vermilion ranges, and the Cuyuna Range.[3] The Animikie Basin was an extensional basin which developed over a basement consisting of the 2,750- to 2,600-million-year-old Superior province to the north and the 3,600-million-year-old Minnesota River Valley subprovince to the south.[2] The extension was caused by the east-northeast–trending Great Lakes tectonic zone; it separates the Superior province from the Minnesota River Valley subprovince.[2] The sediments were deformed, metamorphosed and intruded by the plutonic rocks of the 1860 ± 50-million-year-old Penokean orogeny.[2]
The rocks of the Animikie Basin form a sequence up to 10km (6.2mi) thick and show a complete transition from a stable shelf environment to deep-water conditions.[2] Irregularities in the basement influenced the thickness of the sequence.[2] The 700km (430mi) by 400km (250mi) basin is an elongated oval parallel to and straddling the Great Lakes tectonic zone.[2]
Development of Animikie Basin
Twenty-seven hundred million years ago the Algoman orogeny formed mountains; these bare mountains eroded for several hundred million years to a broad level peneplain.[4]:6 A sea invaded central Minnesota and extended eastward through northern Wisconsin and the Upper Peninsula of Michigan.[4]:6 Sediments composed of quartz-rich sand were deposited along the shoreline of this sea; these were succeeded by thick iron-rich layers and eventually kilometers of mud and muddy sand.[4]:6 The deposition of sedimentary strata on top of the Archean basement formed the Animikie Group.[4]:6
The next tectonic event was the Great Lakes tectonic zone which began with compression caused by the collision of the Superior province and the Minnesota River Valley subprovince during the Algoman orogeny about 2,700 million years ago;[5] it continued as a pulling apart (extensional) rift from 2,450 to 2,100 million years ago,[6]:145 followed by a second compression which deformed the rocks in the Lake Superior region during the Penokean orogeny which lasted from 1,900 to 1,850 million years ago.[7] The first deposits occurred during the initial stages of extension of the Great Lakes tectonic zone in the continental crust.[5]:3 As the crust expanded it thinned, and magma was intruded through fissures in the thinned crust.[5]:3 Sedimentation stopped during this transitional period because the elevation was now above sea level.[5]:3 During later stages, the spreading center was adding oceanic crust – which is heavier than continental crust – so the area subsided, seas returned, and the second layer of sediments were deposited unconformably on the basin fill.[5]:3

The third tectonic event was the Penokean orogeny which is dated 1,850 million years ago.[4]:7 The intense, northward-directed compression folded the shale and greywacke of the southernmost unit – the Thomson Formation – and metamorphosed the shale into slate.[4]:7 The Animikie strata on the Gunflint and Mesabi ranges were far enough away so they escaped this deformation and metamorphism; they contain some of the oldest unmetamorphosed sedimentary deposits in the world.[4]:7

About  million years ago a fourth tectonic event occurred in the Lake Superior region.[4]:7 A hotspot of magma from the earth's mantle beneath present-day Lake Superior rose, causing the crust to dome and break apart.[4]:7 This zone of crustal thinning and fracturing is the Midcontinent Rift System; it extends in a boomerang shape for over 2,200km (1,400mi) from northeastern Kansas northward through Iowa, under the Twin Cities of Minnesota, beneath Lake Superior, and then south through the eastern Upper Peninsula of Michigan and beneath the central Lower Peninsula of Michigan.[4]:7 As the crust was being stretched thin and more magma flowed out from below, the center of the rift was continuously subsiding.[4]:8 The vast quantities of rising magma created a vacuum under the crust, the weight of the solidified magma on the surface caused the crust to subside into that vacuum so the edges of the rift tilted toward the center.[4]:8 The rifting stopped after a few million years; one reason could be that the Grenville orogeny stopped the rift process when that collision occurred.[4]:9 Subsidence continued for several million years after the lava flows had ceased; immense volumes of sediments – sand, gravel and mud – were eroded off the barren landscape into the still-sinking basin along the rift axis.[4]:9 As much as 8km (5.0mi) of sedimentary rocks accumulated in the center before the sinking stopped and the region stabilized.[4]:9 A north-northeast trending branch of the Midcontinent Rift System separated the Animikie Basin into two distinct segments; the present-day Animikie Group and the Marquette Range Supergroup;[8] the historical name for the Marquette Range Supergroup is the Animikie Series.
Banded-iron formations

Oceanic sediments associated with the last stage of the Great Lakes tectonic zone contain the banded-iron formations.[5]:4 Banded-iron formations are iron formations which formed about 2,000 million years ago and were first described in the Lake Superior region.[9] They are characterized by interlayers – bands – of iron minerals and chert (quartz).[9] These sediments were laid down for two hundred million years and extend intermittently along roughly the same trend as the Great Lakes tectonic zone, from Minnesota into eastern Canada, and through upper Wisconsin and Michigan.[5]:4
Change in atmospheric oxygen levels
Banded-iron sediments record the introduction of abundant free oxygen into earth's atmosphere.[5]:2 Microbial life played an important role in changing atmospheric conditions by releasing free oxygen as a waste product of photosynthesis.[5]:2 Free oxygen was taken up by elements with strong affinities for it – hydrogen, carbon and iron.[5]:2 Evidence for the change in oxygen levels is that the sediments of the earlier Archean are dark brown and black caused by unoxidized carbon, iron sulfide, and other elements and compounds.[5]:2 As oxygen levels increased in the atmosphere and oceans, the sediments changed.[5]:2 In the late Archean, sediments went through a transitional stage with the banded-iron formations; after this transition they demonstrate an oxygen-rich environment – shown by iron oxide-stained siltstones or mudstones called red beds.[5]:2
Enough oxygen had accumulated in seawater so that dissolved iron – which had earlier eroded from the surrounding land – was oxidized.[9] Oxygenated water has low levels of dissolved iron because iron reacts with oxygen to form compounds that precipitate out;[10] the compounds include hematite (Fe2O3), limonite (Fe2O3·2H2O) and siderite (FeCO3).[9] These iron compounds precipitated from the sea water in varying proportions with chert, producing banded-iron formations.[9] Banded-iron formations occur in several ranges around the margins of this basin, five of which contained sufficient concentrations of iron to be economically mined.[2] These banded-iron formations have been one of the world's greatest sources of iron ore since mining began in the area during the late 19th century.[4]:7 Major iron formations in different parts of the basin represent either nearly contemporaneous shelf sedimentation on either side of the main basin, or deposits formed simultaneously in isolated sub-basins of the main basin.[2]
Effect of the Sudbury Impact on atmospheric oxygen levels
A 25 to 70cm (9.8 to 27.6in) thick lateral layer between the (meta)sedimentary Gunflint Iron Formation and overlying Rove Formation, and between the Biwabik Iron Formation and overlying Virginia Formation has evidence that the layer contains hypervelocity impact ejecta.[11] Radiometric dating reveals that this layer was deposited between 1,878 and 1,836 million years ago.[11] The Sudbury Impact event – which occurred 650 to 875km (404 to 544mi) to the east 1,850 ± 1 million years ago – is the likely ejecta source, making these the oldest ejecta linked to a specific impact.[11] Additional evidence indicates a 16km (10mi) diameter meteorite collided with earth[12] in the current-day vicinity of Sudbury, Ontario, Canada.[13] The meteorite vaporized and created a 240km (150mi) wide crater.[12] Earthquakes shattered the ground hundreds of kilometers away and within seconds ejecta (cloud of ash, rock fragments, gases and droplets of molten rock) began to spread around the globe.[12] It is estimated that at ground zero the earthquake would have registered 10.2 on the Richter magnitude scale.[12]
To put the Sudbury meteorite impact in perspective, the Chicxulub impact on the Yucatán Peninsula occurred  million years ago with the impact of a 16.5km (10.3mi) diameter comet.[14] The kinetic energy from this impact probably generated earthquakes registering 13 on the Richter scale.[15]:334 The results of this impact caused the worldwide extinction of many species (including dinosaurs).[12] The Sudbury Impact would have also had global ramifications;[12] it is conjectured that this caused the end of the banded-iron deposits. The results of the impact fundamentally affected concentrations of dissolved oxygen in the sea; the accumulation of marine sediments (the banded-iron formations) were almost instantaneously shut down and banded-iron formation buildups suddenly ended about  million years ago.[13] In northeastern Minnesota these iron-banded formations lie immediately under the ejecta layer.[13]
One use of the impact layer is as a precise timeline that ties together well-known stratigraphic sequences of the various geographically separated iron ranges.[16] The Sudbury Impact layer lies at a horizon that records a significant change in the character of sediments across the region.[16] The layer marks the end of a major period of banded-iron formation deposition that was succeeded by deposition of fine clastic rocks – commonly black shales.[16]
End of deposition
Sedimentation styles of the passive margin changed as deposition came to a close.[5]:4 The sedimentary environment recorded near the end changed from deep water shales derived from Archean rocks to coarser clastic rocks derived from a younger Proterozoic source.[5]:4 This change is interpreted to be from the Pembine-Wausau island arc as it closed in from the south just before its collision during the Penokean orogeny.[5]:4 Sediments shedding off the island arc settled on top of the previously deposited sequences.
Formations within Animikie Group
Gunflint Range

The Gunflint Range is a mountain range in northeastern Minnesota, U.S., and western Ontario, Canada. The Gunflint and Mesabi ranges form a belt extending from the upper Mississippi River to the extreme northeast part of Minnesota and into Canada to Thunder Bay.[17]:4 The two ranges are separated by the 1,099-million-year-old Duluth Complex which was formed during the Midcontinent Rift.[18]
The Gunflint Iron Formation is 1,878 ± 2 million years old.[19] It lies on top of a basal conglomerate, unlike the Biwabik Iron Formation which was deposited on top of the Pokegama Quartzite in the Mesabi Range, and the Cuyuna Iron Formation which was deposited on top of the Mille Lacs and North ranges. It is 150km (93mi) long, less than 8km (5.0mi) wide,[20] and 135 to 170m (443 to 558ft) thick.[21] This iron formation lies in a northeasterly-trending belt; most of it lies in Ontario.[20]

The upper sedimentary layer is the 1,800- to 1,600-million-year-old Rove Formation.[1] The seas and laid down the shales, slates and mudstones of the Rove Formation.[22]:6 Because the formation is on the northern part of the Animikie Basin these rocks escaped the crustal deformation from the Penokean orogeny that characterizes the equivalent strata of the Thomson Formation; this left the Rove Formation unmetamorphosed and lying flat.[4]:59 These are some of the oldest undeformed and unmetamorphosed sedimentary rocks in North America.[4]:59 The dikes and sills within the Rove Formation were intruded during the Midcontinent Rift.[4]:61
Mesabi Range
The Mesabi Range is over 320km (200mi) long and less than 16km (9.9mi) wide– its typical width is 4km (2.5mi)[17]:4 – and 110 to 240m (360 to 790ft) thick.[21] Its natural ore is hematite- or geothite-rich leached iron formation;[1] natural ores contain up to 50% iron and less than 10% silica.[5]:4 These thick sedimentary layers contain millions of tons of iron and minor ores which have been mined in the Great Lakes region since before the turn of the 20th century.[5]:4 Sedimentation ended when the Penokean orogeny began  million years ago.[5]:4
The three different formations exposed along the Mesabi Iron Range were deposited along the leading edge of a foredeep basin – the Animikie Basin – which transgressed north over the Archean craton during the Penokean orogeny.[1] Deposition of the basal Pokegama Quartzite, the medial Biwabik Iron Formation and the upper Virginia Formation's sediments represent near-shore, shelf and slope environments, respectively.[1] These three layers were formed 2,500 to 1,600 million years ago.[1]
Pokegama Quartzite occupies the lowest level of the Mesabi Range sequence and is younger than 2,500 million years old.[1] It contains shale, siltstone and sandstone, which were deposited in a flat environment of the sea that covered the Archean surface.[1] It is 0 to 153m (0 to 502ft) thick, with an average of 60m (200ft).[23]:167
The 1,900- to 1,850-million-year-old Biwabik Iron Formation is a narrow belt of iron-rich strata that extends east-northeast for 200km (120mi);[24] its thickness varies from 60 to 600m (200 to 1,970ft), its average may be 305m (1,001ft).[23]:168 It has four primary subdivisions: the Lower Cherty (which was deposited upon the Pokegama Quartzite), the Lower Slatey, the Upper Cherty and the Upper Slaty (which the Virginia Formation rests upon).[25]:928 The two ore-producing layers are the Upper and Lower Cherty subdivisions;[25] cherts make up the bulk of the formation.[23]:167 The east end of the Biwabik Iron Formation was metamorphosed by the heat of the Duluth Complex.[23]:168[26][27]
The 1,850-million-year-old Virginia Formation is the sedimentary layer on top of the Biwabik Iron Range and forms the footwall of the 1,100-million-year-old Duluth Complex[28] in the Ely – Hoyt Lakes region.[29]:24 The Virginia formation consists of black to dark gray argillite,[29]:25 which does not crop out in natural exposures.[30]:41
Vermilion Range

The Vermilion Range is north of the Mesabi Iron Range; it is 154km (96mi) long and ranges from 3 to 30km (1.9 to 18.6mi) wide.[23]:169 Its basal unit is the Ely Greenstone layer. Ely Greenstone consists of igneous rocks which were metamophosed by the gabbro of the Duluth Complex.[23]:169 The Ely Greenstone is a belt consisting chiefly of metamorphosed volcanic rocks which have been deformed so that original bedding stands nearly vertical.[31] In the Soudan area the Ely Greenstone has been tightly folded and slightly overturned southward into the Tower-Soudan anticline, and bedding is inclined 70-80° to the north.[31] The volcanic rocks of the Ely Greenstone are divided into a lower and upper sequence; the upper and lower volcanic sequences are separated by the Soudan Iron Formation – a 50 to 3,000m (160 to 9,840ft) thick unit that is transitional with the Ely Greenstone – which consists chiefly of banded iron-formation.[31] The Soudan Iron Formation is in the western part of the Vermilion Range.[23]:169 It is in narrow belts, and consists of cherts, hematite, magnetite and small amounts of pyrite.[23]:170 The narrow belts trend east–northeast with the widest part to the southwest.[32]:21 These iron-bearing rocks are of sedimentary origin which overlie an igneous series.[23]:170 The iron formation is tightly folded with greenstone.[23]:170 and is overlain by granites in the Vermilion, Trout, Burntside, Basswood and Saganaga lake areas.[23]:169
Cuyuna Range

The Cuyuna Iron Range is southwest of the Mesabi Range in east-central Minnesota; it is 110km (68mi) by 32km (20mi) of tightly folded iron formations.[2] Its thickness ranges from 0 to 135m (0 to 443ft).[21] Two sequences – the Mille Lacs and North ranges – underlie the southern part of the Animike Group.[5]:4 The Mille Lacs Group is more than 2,197 ± 39 million years old.[2]
The North Range Group is the basal unit for the Cuyuna Range. It is divided into three structural units: South Range (The rocks of the South Range are assigned to the Mille Lacs group.),[33] North Range and the Emily District each with its own characteristic stratigraphy and structure.[33] The rocks of the South and North ranges are separated by a major north-verging thrust fault, and both are overlain unconformably by the Emily District.[33] The rocks of the North Range – assigned to the North Range Group,[33] – are divided into three formations, the Mahnomen, Trommald and Rabbit Lake.[33] The North Range of the Cuyuna Range was regionally metamorphosed during the Penokean orogeny, which peaked between 1,870 and 1,850 million years ago.[33] The iron ore of the Cuyuna is a Lake Superior-type iron-formation similar to other iron formations in the region.[9]
The Mahnomen Formation has a lower member, which lacks iron oxide components, and an upper member dominated by beds of iron oxide argillite and lean iron-formation interlayered with non-iron oxide argillite, siltstone and quartzose sandstone.[33] The Trommald Formation – the principal iron formation of the North Range – is a chemically precipitated unit.[33] This formation is 14 to 150m (46 to 492ft) thick and is composed of carbonate-silicate iron formations and associated manganese oxide deposits.[2] The iron oxidised to form hematite and goethite.[2][34] The uppermost Rabbit Lake Formation has a lower member of black mudstone inserted with beds of iron formation and units of volcanogenic origin; and an upper member of slate, carbonaceous mudstone, greywacke and thin units of iron-rich strata.[33]

The top sedimentary layer is the Thomson Formation which was deposited 1,880 to 1,870 million years ago and deformed by the Penokean orogeny 1,850 million years ago.[1] The formation contains folded and metamorphosed greywacke, siltstone, mudstone and slate[1] which were originally deposited in the sea as horizontal beds of mud and sand; the Penokean orogeny subjected the rocks to intense compression from the south.[4]:26 This folded the layers into east-west trending anticlines and synclines, and compressed the muddy beds into slate, a metamorphic rock.[4]:26 The Thomson Formation has steeply dipping beds of greywacke, siltstone and slate.[1] Several basaltic dikes, from the lava of the Midcontinent Rift period, cut across the Thomson Formation slate and greywackes.[4]:28 Most of these dikes trend in a northeasterly direction; they represent magma that rose in fissures in the crust.[4]:28
Summary of Huronian and Marquette Range supergroups
The Huronian and Marquette Range supergroups are similar sedimentary groups to the Animikie Group; all three are in the Great Lakes region. Rifting of continental plates create sedimentary basins; the largest of these basins in the Great Lakes area are the Animikie Group in Minnesota, the Marquette Range Supergroup in northern Michigan and Wisconsin, and the Huronian Supergroup in eastern Ontario.[5]:4
Huronian Supergroup
The Huronian Supergroup on the north shore of Lake Huron in Ontario[35] overlies an Archean basement.[36] On the map it is the formation north of both Lake Huron and the Grenville Front Tectonic Zone. Huronian sedimentary rocks form a 300km (190mi) east–west fold belt and reach a thickness of 12km (7.5mi) near Lake Huron.[37]:266 Deposition of sediments began 2,450 to 2,219 million years ago and continued until 1,850 to 1,800 million years ago when the rocks were deformed and metamorphosed during the Penokean orogeny.[37]:264–6 The supergroup's sedimentary layers are divided into lower and upper sequences.[37]:265 The lower sequence is subdivided into the Elliot Lake, Hough Lake and Quirke Lake groups; the upper sequence is the Cobalt Group.[37]:265 The lower sequences were deposited in a continental rift basin and the upper sequence was deposited in a stable passive margin.[37]:267
Marquette Range Supergroup
The Marquette Range Supergroup also overlies an Archean basement.[36] Originally termed the Animikie Series, it was proposed to be renamed in 1970 to avoid confusion with the Animikie Group in Ontario and Minnesota.[38] On the map it is the dark grey area south of Lake Superior with four iron ranges shown. This supergroup consists of the Chocolay, Menominee, Baraga and Paint River groups,[35] in descending order of age. The Chocolay Group – up to 160m (520ft) thick[39] – is a shallow-marine layer which was deposited on the Archean basement;[19] deposition in the Chocolay Group began 2,207 ± 5 million years ago and ended 2,115 ± 5 million years ago.[40] The Menominee Group is a foredeep deposit whose layers were deposited in second-order basins created by oblique subduction of the continental margin, rather than in basins formed on a rifting margin.[19] The upper Baraga Group represents deeper marine basins resulting from increased subsidence and continued collision.[19] Deposition continued until  million years ago[5]:4 when the Penokean orogeny began.[41]
See also
Stromatolite

How large is the area of the Animikie Group?


This is a list of oil-producing countries by oil exports based on The World Factbook  and other Sources.[1] Many countries also import oil, and some import more oil than they export.
Countries

Oil export revenues
Academic contributions have written about differences in petroleum revenue management in various countries. Many scholars see the natural resource wealth in some countries as a natural resource blessing, while in others it has been referred to as a natural resource curse.[2] A vast body of resource curse literature has studied the role of governance regimes, legal frameworks and political risk in building an economy based on natural resource exploitation.[3][4][5] However, whether it is seen as a blessing or a curse, the recent political decisions regarding the future of petroleum production in many countries were given an extractivist direction, thus also granting a status quo to the exploitation of natural resources.[6]
The PRIX index forecasts the effect of political developments on exports from major petroleum-producing countries.[7]
See also
List of countries by oil production
List of countries by exports
List of countries by net oil exports

What is the largest exporter of petroleum?


The Cyrillic script /sɪˈrɪlɪk/ is a writing system used for various alphabets across Eurasia, particularly in Eastern Europe, the Caucasus, Central Asia, and North Asia. It is based on the Early Cyrillic alphabet developed during the 9th century AD at the Preslav Literary School in the First Bulgarian Empire.[4][5][6] It is the basis of alphabets used in various languages, especially those of Orthodox Slavic origin, and non-Slavic languages influenced by Russian. As of 2011, around 250 million people in Eurasia use it as the official alphabet for their national languages, with Russia accounting for about half of them.[7] With the accession of Bulgaria to the European Union on 1 January 2007, Cyrillic became the third official script of the European Union, following Latin and Greek.[8]
Cyrillic is derived from the Greek uncial script, augmented by letters from the older Glagolitic alphabet, including some ligatures. These additional letters were used for Old Church Slavonic sounds not found in Greek. The script is named in honor of the two Byzantine  brothers,[9] Saints Cyril and Methodius, who created the Glagolitic alphabet earlier on. Modern scholars believe that Cyrillic was developed and formalized by early disciples of Cyril and Methodius.
In the early 18th century, the Cyrillic script used in Russia was heavily reformed by Peter the Great, who had recently returned from his Grand Embassy in western Europe. The new letterforms became closer to those of the Latin alphabet; several archaic letters were removed and several letters were personally designed by Peter the Great (such as Я, which was inspired by the Latin R). West European typography culture was also adopted.[10]
Letters
Cyrillic script spread throughout the East Slavic and some South Slavic territories, being adopted for writing local languages, such as Old East Slavic. Its adaptation to local languages produced a number of Cyrillic alphabets, discussed hereafter.

The early Cyrillic alphabet[11][12]АБВГДЕЖЅ[13]ꙀИІКЛМНОПРСТОУ[14]ФХѠЦЧШЩЪЪІ[15]ЬѢꙖѤЮѪѬѦѨѮѰѲѴҀ[16]
Capital and lowercase letters were not distinguished in old manuscripts.

Yeri (Ы) was originally a ligature of Yer and I (Ъ + І = Ы). Iotation was indicated by ligatures formed with the letter І: Ꙗ (not an ancestor of modern Ya, Я, which is derived from Ѧ), Ѥ, Ю (ligature of І and ОУ), Ѩ, Ѭ. Sometimes different letters were used interchangeably, for example И = І = Ї, as were typographical variants like О = Ѻ.  There were also commonly used ligatures like ѠТ = Ѿ.
The letters also had numeric values, based not on Cyrillic alphabetical order, but inherited from the letters' Greek ancestors.

Cyrillic numerals123456789АВГДЄЅЗИѲ102030405060708090ІКЛМНѮѺПЧ (Ҁ)100200300400500600700800900РСТѴФХѰѾЦ
The early Cyrillic alphabet is difficult to represent on computers. Many of the letterforms differed from those of modern Cyrillic, varied a great deal in manuscripts, and changed over time. Few fonts include glyphs sufficient to reproduce the alphabet. In accordance with Unicode policy, the standard does not include letterform variations or ligatures found in manuscript sources unless they can be shown to conform to the Unicode definition of a character.
The Unicode 5.1 standard, released on 4 April 2008, greatly improves computer support for the early Cyrillic and the modern Church Slavonic language. In Microsoft Windows, the Segoe UI user interface font is notable for having complete support for the archaic Cyrillic letters since Windows 8.

Letters of the Cyrillic alphabet (see also Cyrillic digraphs)А
AБ
BeВ
VeГ
GeҐ
Ghe upturnД
DeЂ
DjeЃ
GjeЕ
YeЁ
YoЄ
Ukrainian YeЖ
ZheЗ
ZeЗ́
ZjeЅ
DzeИ
IІ
Dotted IЇ
YiЙ
Short IЈ
JeК
KaЛ
ElЉ
LjeМ
EmН
EnЊ
NjeО
OП
PeР
ErС
EsС́
SjeТ
TeЋ
TsheЌ
KjeУ
UЎ
Short UФ
EfХ
KhaЦ
TseЧ
CheЏ
DzheШ
ShaЩ
ShchaЪ
Hardsign (Yer)Ы
YeryЬ
Softsign (Yeri)Э
EЮ
YuЯ
YaImportant Cyrillic non-Slavic lettersӀ
PalochkaӘ
Cyrillic SchwaҒ
AynҘ
Bashkir DheҪ
Bashkir TheҠ
Bashkir QaҖ
ZhjeҚ
Ka with
descenderҢ
NgҤ
En-gheӨ
Barred OҮ
Straight UҰ
Straight U
with strokeҺ
Shha (He)Ҳ
Kha with
descenderӐ
A with
breveCyrillic letters used in the pastꙖ
AiotifiedѤ
EiotifiedѦ
YussmallѪ
YusbigѨ
Yussmall iotifiedѬ
Yusbig iotifiedѮ
KsiѰ
PsiꙞ
YnѲ
FitaѴ
IzhitsaѶ
Izhitsa okovyҀ
KoppaОУ
UkѠ
OmegaѾ
OtѢ
Yat
Letterforms and typography
The development of Cyrillic typography passed directly from the medieval stage to the late Baroque, without a Renaissance phase as in Western Europe. Late Medieval Cyrillic letters (still found on many icon inscriptions today) show a marked tendency to be very tall and narrow, with strokes often shared between adjacent letters.
Peter the Great, Czar of Russia, mandated the use of westernized letter forms in the early 18th century. Over time, these were largely adopted in the other languages that use the script. Thus, unlike the majority of modern Greek fonts that retained their own set of design principles for lower-case letters (such as the placement of serifs, the shapes of stroke ends, and stroke-thickness rules, although Greek capital letters do use Latin design principles), modern Cyrillic fonts are much the same as modern Latin fonts of the same font family. The development of some Cyrillic computer typefaces from Latin ones has also contributed to the visual Latinization of Cyrillic type.

Cyrillic uppercase and lowercase letter forms are not as differentiated as in Latin typography. Upright Cyrillic lowercase letters are essentially small capitals (with exceptions: Cyrillic ⟨а⟩, ⟨е⟩, ⟨і⟩, ⟨ј⟩, ⟨р⟩, and ⟨у⟩ adopted Western lowercase shapes, lowercase ⟨ф⟩ is typically designed under the influence of Latin ⟨p⟩, lowercase ⟨б⟩, ⟨ђ⟩ and ⟨ћ⟩ are traditional handwritten forms), although a good-quality Cyrillic typeface will still include separate small-caps glyphs.[17]
Cyrillic fonts, as well as Latin ones, have roman and italic types (practically all popular modern fonts include parallel sets of Latin and Cyrillic letters, where many glyphs, uppercase as well as lowercase, are simply shared by both). However, the native font terminology in most Slavic languages (for example, in Russian) does not use the words "roman" and "italic" in this sense.[18] Instead, the nomenclature follows German naming patterns:

Roman type is called pryamoy shrift ("upright type")—compare with Normalschrift ("regular type") in German
Italic type is called kursiv ("cursive") or kursivniy shrift ("cursive type")—from the German word Kursive, meaning italic typefaces and not cursive writing
Cursive handwriting is rukopisniy shrift ("handwritten type") in Russian—in German: Kurrentschrift or Laufschrift, both meaning literally 'running type'
As in Latin typography, a sans-serif face may have a mechanically sloped oblique type (naklonniy shrift—"sloped", or "slanted type") instead of italic.
Similarly to Latin fonts, italic and cursive types of many Cyrillic letters (typically lowercase; uppercase only for handwritten or stylish types) are very different from their upright roman types. In certain cases, the correspondence between uppercase and lowercase glyphs does not coincide in Latin and Cyrillic fonts: for example, italic Cyrillic ⟨т⟩ is the lowercase counterpart of ⟨Т⟩ not of ⟨М⟩.
A boldfaced type is called poluzhirniy shrift ("semi-bold type"), because there existed fully boldfaced shapes that have been out of use since the beginning of the 20th century. A bold italic combination (bold slanted) does not exist for all font families.
In Standard Serbian, as well as in Macedonian,[19] some italic and cursive letters are allowed to be different to resemble more to the handwritten letters. The regular (upright) shapes are generally standardized among languages and there are no officially recognized variations.[20]
The following table shows the differences between the upright and italic Cyrillic letters of the Russian alphabet. Italic forms significantly different from their upright analogues, or especially confusing to users of a Latin alphabet, are highlighted.

Also available as a .абвгдеёжзийклмнопрстуфхцчшщъыьэюяабвгдеёжзийклмнопрстуфхцчшщъыьэюя
Note: in some fonts or styles, lowercase italic Cyrillic ⟨д⟩ (⟨д⟩) may look like Latin ⟨g⟩ and lowercase italic Cyrillic ⟨т⟩ (⟨т⟩) may look exactly like a capital italic ⟨T⟩ (⟨T⟩), only smaller.

Cyrillic alphabets

Among others, Cyrillic is the standard script for writing the following languages:
Slavic languages: Belarusian, Bulgarian, Macedonian, Russian, Rusyn, Serbo-Croatian (for Standard Serbian, Bosnian, and Montenegrin), Ukrainian
Non-Slavic languages: Abkhaz, Aleut (now mostly in church texts), Bashkir, Chuvash, Erzya, Kazakh (to be replaced by Latin script by 2025[1]), Kildin Sami, Komi, Kyrgyz, Dungan, Mari, Moksha, Mongolian, Ossetic, Romani (some dialects), Sakha/Yakut, Tajik, Tatar, Tlingit (now only in church texts), Tuvan, Udmurt, Yuit (Siberian Yupik), and Yupik (in Alaska).
The Cyrillic script has also been used for languages of Alaska,[21] Slavic Europe (except for Western Slavic and some Southern Slavic), the Caucasus, Siberia, and the Russian Far East.
The first alphabet derived from Cyrillic was Abur, used for the Komi language. Other Cyrillic alphabets include the Molodtsov alphabet for the Komi language and various alphabets for Caucasian languages.
Name
Since the script was conceived and popularised by the followers of Cyril and Methodius, rather than by Cyril and Methodius themselves, its name denotes homage rather than authorship. The name "Cyrillic" often confuses people who are not familiar with the script's history, because it does not identify a country of origin (in contrast to the "Greek alphabet"). Among the general public, it is often called "the Russian alphabet," because Russian is the most popular and influential alphabet based on the script. Some Bulgarian intellectuals, notably Stefan Tsanev, have expressed concern over this, and have suggested that the Cyrillic script be called the "Bulgarian alphabet" instead, for the sake of historical accuracy.[22]
In Bulgarian, Macedonian, Russian, and Serbian, the Cyrillic alphabet is also known as azbuka, derived from the old names of the first two letters of most Cyrillic alphabets (just as the term alphabet came from the first two Greek letters alpha and beta).
History

History of the alphabet
Egyptian hieroglyphs 32 c. BCE
Hieratic 32 c. BCE
Demotic 7 c. BCE
Meroitic 3 c. BCE
Proto-Sinaitic 19 c. BCE
Ugaritic 15 c. BCE
Epigraphic South Arabian 9 c. BCE
Ge’ez 5–6 c. BCE
Canaanite-Phoenician alphabet 12 c. BCE
Paleo-Hebrew 10 c. BCE
Samaritan 6 c. BCE
Libyco-Berber 3 c. BCE
Tifinagh
Paleohispanic (semi-syllabic) 7 c. BCE
Aramaic 8 c. BCE
Kharoṣṭhī 4 c. BCE
Brāhmī 4 c. BCE
Brahmic family (see) E.g.
Tibetan 7 c. CE
ʼPhags-pa script 13 c. CE
Devanagari 10 c. CE
Canadian syllabics 1840 CE
Hebrew 3 c. BCE
Pahlavi 3 c. BCE
Avestan 4 c. CE
Palmyrene 2 c. BCE
Syriac 2 c. BCE
Nabataean 2 c. BCE
Arabic 4 c. CE
N'Ko 1949 CE
Sogdian 2 c. BCE
Orkhon (old Turkic) 6 c. CE
Old Hungarian c. 650 CE
Old Uyghur
Mongolian 1204 CE
Mandaic 2 c. CE
Greek 8 c. BCE
Etruscan 8 c. BCE
Latin 7 c. BCE
Cherokee (syllabary; letter forms only) c. 1820 CE
Runic 2 c. CE
Ogham (origin uncertain) 4 c. CE
Coptic 3 c. CE
Gothic 3 c. CE
Armenian 405 CE
Georgian (origin uncertain) c. 430 CE
Glagolitic 862 CE
Cyrillic c. 940 CE
Old Permic 1372 CE
Mesopotamian cuneiform 32 c. BCE
Ugaritic (shape influenced) 15 c. BCE
Old Persian cuneiform (apparently inspired) 525 BCE
Indus script 26 c. BCE
Cretan hieroglyphs (possible ancestor of Linear A) 21 c. BCE
Linear A 18 c. BCE
Linear B 15 c. BCE
Cypro-Minoan syllabary 16 c. BCE
Cypriot syllabary 11 c. BCE
Chinese Characters 13 c. BCE
Chinese family (see) E.g.
Kana 800 CE
Chữ Nôm 13 c. CE
Zhuyin 1913 CE
Mesoamerican family (see) E.g.
Maya script 3 c. BCE
Ogham (origin uncertain) 4 c. CE
Dongba symbols 10 c. CE
Hangul 1443 CE
Yi script 15 c. CE (syllabic version established in 1974)
Thaana 18 c. CE (derived from Brahmi numerals)
Osmanya alphabet 1920s CE
Santali alphabet (or Ol Chiki script) 1925 CE
Borama alphabet 1933 CE
Kaddare script (resembling Osmanya script and Brahmi script.) 1952 CEvt
The Cyrillic script was created in the First Bulgarian Empire.[23] Its first variant, the Early Cyrillic alphabet, was created at the Preslav Literary School. It is derived from the Greek uncial script letters, augmented by ligatures and consonants from the older Glagolitic alphabet for sounds not found in Greek. Tradition holds that Cyrillic and Glagolitic were formalized either by Saints Cyril and Methodius who brought Christianity to the southern Slavs, or by their disciples.[24][25][26][27] Paul Cubberley posits that although Cyril may have codified and expanded Glagolitic, it was his students in the First Bulgarian Empire under Tsar Simeon the Great that developed Cyrillic from the Greek letters in the 890s as a more suitable script for church books.[23] Later Cyrillic spread among other Slavic peoples, as well as among non-Slavic Vlachs.
Cyrillic and Glagolitic were used for the Church Slavonic language, especially the Old Church Slavonic variant. Hence expressions such as "И is the tenth Cyrillic letter" typically refer to the order of the Church Slavonic alphabet; not every Cyrillic alphabet uses every letter available in the script.
The Cyrillic script came to dominate Glagolitic in the 12th century. The literature produced in the Old Bulgarian language soon spread north and became the lingua franca of the Balkans and Eastern Europe, where it came to also be known as Old Church Slavonic.[28][29][30][31][32] The alphabet used for the modern Church Slavonic language in Eastern Orthodox and Eastern Catholic rites still resembles early Cyrillic. However, over the course of the following millennium, Cyrillic adapted to changes in spoken language, developed regional variations to suit the features of national languages, and was subjected to academic reform and political decrees. A notable example of such linguistic reform can be attributed to Vuk Stefanović Karadžić who updated the Serbian Cyrillic alphabet by removing certain graphemes no longer represented in the vernacular, and introducing graphemes specific to Serbian (i.e. Љ Њ Ђ Ћ Џ Ј), distancing it from Church Slavonic alphabet in use prior to the reform. Today, many languages in the Balkans, Eastern Europe, and northern Eurasia are written in Cyrillic alphabets.
Relationship to other writing systems
Latin script

A number of languages written in a Cyrillic alphabet have also been written in a Latin alphabet, such as Azerbaijani, Uzbek, Serbian and Romanian (in the Republic of Moldova until 1989, in Romania throughout the 19th century). After the disintegration of the Soviet Union in 1991, some of the former republics officially shifted from Cyrillic to Latin. The transition is complete in most of Moldova (except the breakaway region of Transnistria, where Moldovan Cyrillic is official), Turkmenistan, and Azerbaijan. Uzbekistan still uses both systems, and Kazakhstan has officially begun a transition from Cyrillic to Latin (scheduled to be complete by 2025). The Russian government has mandated that Cyrillic must be used for all public communications in all federal subjects of Russia, to promote closer ties across the federation. This act was controversial for speakers of many Slavic languages; for others, such as Chechen and Ingush speakers, the law had political ramifications. For example, the separatist Chechen government mandated a Latin script which is still used by many Chechens. Those in the diaspora especially refuse to use the Chechen Cyrillic alphabet, which they associate with Russian imperialism.

Standard Serbian uses both the Cyrillic and Latin scripts. Cyrillic is nominally the official script of Serbia's administration according to the Serbian constitution;[33] however, the law does not regulate scripts in standard language, or standard language itself by any means. In practice the scripts are equal, with Latin being used more often in a less official capacity.[34]
The Zhuang alphabet, used between the 1950s and 1980s in portions of the People's Republic of China, used a mixture of Latin, phonetic, numeral-based, and Cyrillic letters. The non-Latin letters, including Cyrillic, were removed from the alphabet in 1982 and replaced with Latin letters that closely resembled the letters they replaced.
Romanization

There are various systems for Romanization of Cyrillic text, including transliteration to convey Cyrillic spelling in Latin letters, and transcription to convey pronunciation.
Standard Cyrillic-to-Latin transliteration systems include:
Scientific transliteration, used in linguistics, is based on the Bosnian and Croatian Latin alphabet.
The Working Group on Romanization Systems[35] of the United Nations recommends different systems for specific languages. These are the most commonly used around the world.
ISO 9:1995, from the International Organization for Standardization.
American Library Association and Library of Congress Romanization tables for Slavic alphabets (ALA-LC Romanization), used in North American libraries.
BGN/PCGN Romanization (1947), United States Board on Geographic Names & Permanent Committee on Geographical Names for British Official Use).
GOST 16876, a now defunct Soviet transliteration standard. Replaced by GOST 7.79, which is ISO 9 equivalent.
Various informal romanizations of Cyrillic, which adapt the Cyrillic script to Latin and sometimes Greek glyphs for compatibility with small character sets.
See also Romanization of Belarusian, Bulgarian, Kyrgyz, Russian, Macedonian and Ukrainian.
Cyrillization
Representing other writing systems with Cyrillic letters is called Cyrillization.
Computer encoding
Unicode

As of Unicode version 11.0, Cyrillic letters, including national and historical alphabets, are encoded across several blocks:
Cyrillic:
Cyrillic Supplement:
Cyrillic Extended-A:
Cyrillic Extended-B:
Cyrillic Extended-C:
Phonetic Extensions:
Combining Half Marks:
The characters in the range U+0400 to U+045F are basically the characters from ISO 8859-5 moved upward by 864 positions. The characters in the range U+0460 to U+0489 are historic letters, not used now. The characters in the range U+048A to U+052F are additional letters for various languages that are written with Cyrillic script.
Unicode as a general rule does not include accented Cyrillic letters. A few exceptions include:
combinations that are considered as separate letters of respective alphabets, like Й, Ў, Ё, Ї, Ѓ, Ќ (as well as many letters of non-Slavic alphabets);
two most frequent combinations orthographically required to distinguish homonyms in Bulgarian and Macedonian: Ѐ, Ѝ;
a few Old and New Church Slavonic combinations: Ѷ, Ѿ, Ѽ.
To indicate stressed or long vowels, combining diacritical marks can be used after the respective letter (for example, U+0301◌́COMBINING ACUTE ACCENT: ы́ э́ ю́ я́ etc.).
Some languages, including Church Slavonic, are still not fully supported.
Unicode 5.1, released on 4 April 2008, introduces major changes to the Cyrillic blocks. Revisions to the existing Cyrillic blocks, and the addition of Cyrillic Extended A (2DE0 ... 2DFF) and Cyrillic Extended B (A640 ... A69F), significantly improve support for the early Cyrillic alphabet, Abkhaz, Aleut, Chuvash, Kurdish, and Moksha.[36]
Other
Punctuation for Cyrillic text is similar to that used in European Latin-alphabet languages.
Other character encoding systems for Cyrillic:
CP866 – 8-bit Cyrillic character encoding established by Microsoft for use in MS-DOS also known as GOST-alternative. Cyrillic characters go in their native order, with a "window" for pseudographic characters.
ISO/IEC 8859-5 – 8-bit Cyrillic character encoding established by International Organization for Standardization
KOI8-R – 8-bit native Russian character encoding. Invented in the USSR for use on Soviet clones of American IBM and DEC computers. The Cyrillic characters go in the order of their Latin counterparts, which allowed the text to remain readable after transmission via a 7-bit line that removed the most significant bit from each byte—the result became a very rough, but readable, Latin transliteration of Cyrillic. Standard encoding of early 1990s for Unix systems and the first Russian Internet encoding.
KOI8-U – KOI8-R with addition of Ukrainian letters.
MIK – 8-bit native Bulgarian character encoding for use in Microsoft DOS.
Windows-1251 – 8-bit Cyrillic character encoding established by Microsoft for use in Microsoft Windows. The simplest 8-bit Cyrillic encoding—32 capital chars in native order at 0xc0–0xdf, 32 usual chars at 0xe0–0xff, with rarely used "YO" characters somewhere else. No pseudographics. Former standard encoding in some GNU/Linux distributions for Belarusian and Bulgarian, but currently displaced by UTF-8.
GOST-main.
GB 2312 – Principally simplified Chinese encodings, but there are also the basic 33 Russian Cyrillic letters (in upper- and lower-case).
JIS and Shift JIS – Principally Japanese encodings, but there are also the basic 33 Russian Cyrillic letters (in upper- and lower-case).
Keyboard layouts

Each language has its own standard keyboard layout, adopted from typewriters. With the flexibility of computer input methods, there are also transliterating or phonetic/homophonic keyboard layouts made for typists who are more familiar with other layouts, like the common English QWERTY keyboard. When practical Cyrillic keyboard layouts or fonts are unavailable, computer users sometimes use transliteration or look-alike "volapuk" encoding to type in languages that are normally written with the Cyrillic alphabet.
See also

Cyrillic (Unicode block)
Cyrillic Alphabet Day
Cyrillic digraphs
Faux Cyrillic, real or fake Cyrillic letters used to give Latin-alphabet text a Soviet or Russian feel
Languages using Cyrillic
List of Cyrillic digraphs
List of Cyrillic letters
Russian cursive
Russian manual alphabet
Yugoslav manual alphabet
Russian Braille
Yugoslav Braille
Vladislav the Grammarian
Internet top-level domains in Cyrillic: gTLDs, .мон, .бг, .қаз, .рф, .срб, .укр
Notes

Ivan G. Iliev. Short History of the Cyrillic Alphabet. Plovdiv. 2012.
Bringhurst, Robert (2002). The Elements of Typographic Style (version 2.5), pp.262–264. Vancouver, Hartley & Marks. ISBN0-88179-133-4.
Nezirović, M. (1992). Jevrejsko-španjolska književnost. Sarajevo: Svjetlost. [cited in Šmid, 2002]
Šmid, Katja (2002). "(603 KiB)", in Verba Hispanica, vol X. Liubliana: Facultad de Filosofía y Letras de la Universidad de Liubliana. ISSN.
'The Lives of St. Tsurho and St. Strahota', Bohemia, 1495, Vatican Library
Philipp Ammon:  in: Sjani (Thoughts) Georgian Scientific Journal of Literary Theory and Comparative Literature, N 17, 2016, pp.248–256

 overview and history of Cyrillic charsets.
, a collection of writing systems and transliteration tables

 review of Cyrillic charsets in Slavic Languages.

, article about the Cyrillic script

Where did the Cyrillic alphabet originate?


Relevant topics onElectrical installations
Wiring practice by region or country
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Regulation of electrical installations
BS 7671 UK wiring regulations
IEC 60364 IEC international standard
Canadian Electrical Code (CEC)
U.S. National Electrical Code (NEC)
Cabling and accessories
AC power plugs and sockets
Cable tray
Electrical conduit
Mineral-insulated copper-clad cable
Multiway switching
Steel wire armoured cable
Ring main unit
Ring circuit
Thermoplastic-sheathed cable
Switching and protection devices
AFCI
ELCB
Electrical busbar system
Circuit breakers
Disconnector
Fuse
Residual Current Device (RCD) / GFCI (USA)
Distribution board
Consumer unit
Electrical switch
Earthing systemvt

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliance, up to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD (Over Current Protection Device).
Origins
An early form of circuit breaker was described by Thomas Edison in an 1879 patent application, although his commercial power distribution system used fuses.[1] Its purpose was to protect lighting circuit wiring from accidental short circuits and overloads. A modern miniature circuit breaker similar to the ones now in use was patented by Brown, Boveri & Cie in 1924. Hugo Stotz, an engineer who had sold his company to BBC, was credited as the inventor on DRP (Deutsches Reichspatent) 458392.[2] Stotz's invention was the forerunner of the modern thermal-magnetic breaker commonly used in household load centers to this day.
Interconnection of multiple generator sources into an electrical grid required the development of circuit breakers with increasing voltage ratings and increased ability to safely interrupt the increasing short-circuit currents produced by networks. Simple air-break manual switches produced hazardous arcs when interrupting high voltages; these gave way to oil-enclosed contacts, and various forms using the directed flow of pressurized air, or of pressurized oil, to cool and interrupt the arc. By 1935, the specially constructed circuit breakers used at the Boulder Dam project use eight series breaks and pressurized oil flow to interrupt faults of up to 2,500 MVA, in three cycles of the AC power frequency.[3]
Operation
All circuit breaker systems have common features in their operation, but details vary substantially depending on the voltage class, current rating and type of the circuit breaker.
The circuit breaker must first detect a fault condition. In small mains and low voltage circuit breakers, this is usually done within the device itself. Typically, the heating or magnetic effects of electric current are employed. Circuit breakers for large currents or high voltages are usually arranged with protective relay pilot devices to sense a fault condition and to operate the opening mechanism. These typically require a separate power source, such as a battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays, and an internal control power source.
Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; this is commonly done using mechanically stored energy contained within the breaker, such as a spring or compressed air to separate the contacts. Circuit breakers may also use the higher current caused by the fault to separate the contacts, such as thermal expansion or a magnetic field. Small circuit breakers typically have a manual control lever to switch off the load or reset a tripped breaker, while larger units use solenoids to trip the mechanism, and electric motors to restore energy to the springs.
The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current. Miniature and molded-case circuit breakers are usually discarded when the contacts have worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.
When a high current or voltage is interrupted, an arc is generated. The length of the arc is generally proportional to the voltage while the intensity (or heat) is proportional to the current. This arc must be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium the arc forms in. Different techniques are used to extinguish the arc including:
Lengthening or deflecting the arc
Intensive cooling (in jet chambers)
Division into partial arcs
Zero point quenching (contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening. The zero crossing occurs at twice the line frequency; i.e., 100 times per second for 50Hz and 120 times per second for 60Hz AC.)
Connecting capacitors in parallel with contacts in DC circuits.
Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.
Arc interruption
Low-voltage miniature circuit breakers (MCB) use air alone to extinguish the arc. These circuit breakers contain so-called arc chutes, a stack of mutually insulated parallel metal plates that divide and cool the arc. By splitting the arc into smaller arcs the arc is cooled down while the arc voltage is increased and serves as an additional impedance that limits the current through the circuit breaker. The current-carrying parts near the contacts provide easy deflection of the arc into the arc chutes by a magnetic force of a current path, although magnetic blowout coils or permanent magnets could also deflect the arc into the arc chute (used on circuit breakers for higher ratings). The number of plates in the arc chute is dependent on the short-circuit rating and nominal voltage of the circuit breaker.
In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.[4]
Gas (usually sulfur hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc.
Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material). The arc quenches when it is stretched a very small amount (less than 2–3mm (0.079–0.118in)). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 38,000 volts.
Air circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.
Circuit breakers are usually able to terminate all current very quickly: typically the arc is extinguished between 30 ms and 150 ms after the mechanism has been tripped, depending upon age and construction of the device. The maximum current value and let-through energy determine the quality of the circuit breakers.
Short-circuit
Circuit breakers are rated both by the normal current that they are expected to carry, and the maximum short-circuit current that they can safely interrupt. This latter figure is the ampere interrupting capacity (AIC) of the breaker.
Under short-circuit conditions, the calculated or measured maximum prospective short-circuit current may be many times the normal, rated current of the circuit. When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. This condition can create conductive ionized gases and molten or vaporized metal, which can cause further continuation of the arc, or creation of additional short circuits, potentially resulting in the explosion of the circuit breaker and the equipment that it is installed in. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc.
The maximum short-circuit current that a breaker can interrupt is determined by testing. Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset.
Typical domestic panel circuit breakers are rated to interrupt 10kA (10000A) short-circuit current.
Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a panel board; these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution-type circuit breakers.
Standard current ratings

Circuit breakers are manufactured in standard sizes, using a system of preferred numbers to cover a range of ratings. Miniature circuit breakers have a fixed trip setting; changing the operating current value requires changing the whole circuit breaker. Larger circuit breakers can have adjustable trip settings, allowing standardized elements to be applied but with a setting intended to improve protection. For example, a circuit breaker with a 400 ampere "frame size" might have its overcurrent detection set to operate at only 300 amperes, to protect a feeder cable.
International Standards, IEC 60898-1 and European Standard EN 60898-1, define the rated current In of a circuit breaker for low voltage distribution applications as the maximum current that the breaker is designed to carry continuously (at an ambient air temperature of 30°C). The commonly available preferred values for the rated current are1A,2A,4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A,[5] and 125A (similar to the R10 Renard series, but using 6, 13, and 32 instead of 6.3, 12.5, and 31.5 – it includes the 13A current limit of British BS 1363 sockets). The circuit breaker is labeled with the rated current in amperes, but excluding the unit symbol, A. Instead, the ampere figure is preceded by a letter, B, C, or D, which indicates the instantaneous tripping current — that is, the minimum value of current that causes the circuit breaker to trip without intentional time delay (i.e., in less than 100ms), expressed in terms of In:

Circuit breakers are also rated by the maximum fault current that they can interrupt; this allows use of more economical devices on systems unlikely to develop the high short-circuit current found on, for example, a large commercial building distribution system.
In the United States, Underwriters Laboratories (UL) certifies equipment ratings, called Series Ratings (or "integrated equipment ratings") for circuit breaker equipment used for buildings. Power circuit breakers and medium- and high-voltage circuit breakers used for industrial or electric power systems are designed and tested to ANSI or IEEE standards in the C37 series.
Types

Many classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features.
Low-voltage
Low-voltage (less than 1,000 VAC) types are common in domestic, commercial and industrial application, and include:
Miniature circuit breaker (MCB)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category.
Molded Case Circuit Breaker (MCCB)—rated current up to 2,500 A. Thermal or thermal-magnetic operation. Trip current may be adjustable in larger ratings.
Low-voltage power circuit breakers can be mounted in multi-tiers in low-voltage switchboards or switchgear cabinets.
The characteristics of low-voltage circuit breakers are given by international standards such as IEC 947. These circuit breakers are often installed in draw-out enclosures that allow removal and interchange without dismantling the switchgear.
Large low-voltage molded case and power circuit breakers may have electric motor operators so they can open and close under remote control. These may form part of an automatic transfer switch system for standby power.
Low-voltage circuit breakers are also made for direct-current (DC) applications, such as DC for subway lines. Direct current requires special breakers because the arc is continuous—unlike an AC arc, which tends to go out on each half cycle. A direct current circuit breaker has blow-out coils that generate a magnetic field that rapidly stretches the arc. Small circuit breakers are either installed directly in equipment, or are arranged in a breaker panel.

The DIN rail-mounted thermal-magnetic miniature circuit breaker is the most common style in modern domestic consumer units and commercial electrical distribution boards throughout Europe. The design includes the following components:
Actuator lever - used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even if the lever is held or locked in the "on" position. This is sometimes referred to as "free trip" or "positive trip" operation.
Actuator mechanism - forces the contacts together or apart.
Contacts - allow current when touching and break the current when moved apart.
Terminals
Bimetallic strip - separates contacts in response to smaller, longer-term overcurrents
Calibration screw - allows the manufacturer to precisely adjust the trip current of the device after assembly.
Solenoid - separates contacts rapidly in response to high overcurrents
Arc divider/extinguisher
Solid State
Solid-state circuit breakers, also known as Digital circuit breakers are a technological innovation which promises advance circuit breaker technology out of the mechanical level, into the electrical. This promises several advantages, such as cutting the circuit in fractions of microseconds, better monitoring of circuit loads and longer lifetimes.
[6]
Magnetic
Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force increases with the current. Certain designs utilize electromagnetic forces in addition to those of the solenoid. The circuit breaker contacts are held closed by a latch. As the current in the solenoid increases beyond the rating of the circuit breaker, the solenoid's pull releases the latch, which lets the contacts open by spring action. They are the most commonly used circuit breakers.
Thermal-magnetic

Thermal magnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions. The thermal portion of the circuit breaker provides a time response feature, that trips the circuit breaker sooner for larger overcurrents but allows smaller overloads to persist for a longer time. This allows short current spikes such as are produced when a motor or other non-resistive load is switched on. With very large over-currents during a short-circuit, the magnetic element trips the circuit breaker with no intentional additional delay.[7]
Magnetic-hydraulic
A magnetic-hydraulic circuit breaker uses a solenoid coil to provide operating force to open the contacts. Magnetic-hydraulic  breakers incorporate a hydraulic time delay feature using a viscous fluid. A spring restrains the core until the current exceeds the breaker rating. During an overload, the speed of the solenoid motion is restricted by the fluid. The delay permits brief current surges beyond normal running current for motor starting, energizing equipment, etc. Short-circuit currents provide sufficient solenoid force to release the latch regardless of core position thus bypassing the delay feature. Ambient temperature affects the time delay but does not affect the current rating of a magnetic breaker. [8]
Large power circuit breakers, applied in circuits of more than 1000 volts, may incorporate hydraulic elements in the contact operating mechanism. Hydraulic energy may be supplied by a pump, or stored in accumulators.  These form a distinct type from oil-filled circuit breakers where oil is the arc extinguishing medium. [9]
Common trip breakers

When supplying a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. To ensure that all live conductors are interrupted when any pole trips, a "common trip" breaker must be used. These may either contain two or three tripping mechanisms within one case, or for small breakers, may externally tie the poles together via their operating handles. Two-pole common trip breakers are common on 120/240-volt systems where 240 volt loads (including major appliances or further distribution boards) span the two live wires. Three-pole common trip breakers are typically used to supply three-phase electric power to large motors or further distribution boards.
Two- and four-pole breakers are used when there is a need to disconnect multiple phase AC, or to disconnect the neutral wire to ensure that no current flows through the neutral wire from other loads connected to the same network when workers may touch the wires during maintenance. Separate circuit breakers must never be used for live and neutral, because if the neutral is disconnected while the live conductor stays connected, a dangerous condition arises: the circuit appears de-energized (appliances don't work), but wires remain live and some residual-current devices (RCDs) may not trip if someone touches the live wire (because some RCDs need power to trip). This is why only common trip breakers must be used when neutral wire switching is needed.
Medium-voltage
Medium-voltage circuit breakers rated between 1 and 72 kV may be assembled into metal-enclosed switchgear line ups for indoor use, or may be individual components installed outdoors in a substation. Air-break circuit breakers replaced oil-filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers (up to about 40.5 kV). Like the high voltage circuit breakers described below, these are also operated by current sensing protective relays operated through current transformers. The characteristics of MV breakers are given by international standards such as IEC 62271. Medium-voltage circuit breakers nearly always use separate current sensors and protective relays, instead of relying on built-in thermal or magnetic overcurrent sensors.
Medium-voltage circuit breakers can be classified by the medium used to extinguish the arc:
Vacuum circuit breakers—With rated current up to 6,300 A, and higher for generator circuit breakers application ( up to 16,000 A & 140 kA). These breakers interrupt the current by creating and extinguishing the arc in a vacuum container - aka "bottle". Long life bellows are designed to travel the 6–10mm the contacts must part. These are generally applied for voltages up to about 40,500 V,[10] which corresponds roughly to the medium-voltage range of power systems. Vacuum circuit breakers have longer life expectancy between overhaul than do other circuit breakers. In addition their Global Warming Potential is by far lower than SF6 circuit breaker.
Air circuit breakers—Rated current up to 6,300 A and higher for generator circuit breakers. Trip characteristics are often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, though some models are microprocessor controlled via an integral electronic trip unit. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.
SF6 circuit breakers extinguish the arc in a chamber filled with sulfur hexafluoride gas.
Medium-voltage circuit breakers may be connected into the circuit by bolted connections to bus bars or wires, especially in outdoor switchyards. Medium-voltage circuit breakers in switchgear line-ups are often built with draw-out construction, allowing breaker removal without disturbing power circuit connections, using a motor-operated or hand-cranked mechanism to separate the breaker from its enclosure.
High-voltage

Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5kV or higher, according to a recent definition by the International Electrotechnical Commission (IEC). High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers. In substations the protective relay scheme can be complex, protecting equipment and buses from various types of overload or ground/earth fault.
High-voltage breakers are broadly classified by the medium used to extinguish the arc:
Bulk oil
Minimum oil
Air blast
Vacuum
SF6
CO2
Due to environmental and cost concerns over insulating oil spills, most new breakers use SF6 gas to quench the arc.
Circuit breakers can be classified as live tank, where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. High-voltage AC circuit breakers are routinely available with ratings up to 765kV. 1,200 kV breakers were launched by Siemens in November 2011,[11] followed by ABB in April the following year.[12]
High-voltage circuit breakers used on transmission systems may be arranged to allow a single pole of a three-phase line to trip, instead of tripping all three poles; for some classes of faults this improves the system stability and availability.
High-voltage direct current circuit breakers are still a field of research as of 2015. Such breakers would be useful to interconnect HVDC transmission systems.[13]
Sulfur hexafluoride (SF6) high-voltage

A sulfur hexafluoride circuit breaker uses contacts surrounded by sulfur hexafluoride gas to quench the arc. They are most often used for transmission-level voltages and may be incorporated into compact gas-insulated switchgear. In cold climates, supplemental heating or de-rating of the circuit breakers may be required due to liquefaction of the SF6 gas.
Disconnecting circuit breaker (DCB)

The disconnecting circuit breaker (DCB) was introduced in 2000[14] and is a high-voltage circuit breaker modeled after the SF6-breaker. It presents a technical solution where the disconnecting function is integrated in the breaking chamber, eliminating the need for separate disconnectors. This increases the availability, since open-air disconnecting switch main contacts need maintenance every 2–6 years, while modern circuit breakers have maintenance intervals of 15 years. Implementing a DCB solution also reduces the space requirements within the substation, and increases the reliability, due to the lack of separate disconnectors.[15][16]
In order to further reduce the required space of substation, as well as simplifying the design and engineering of the substation, a fiber optic current sensor (FOCS) can be integrated with the DCB. A 420 kV DCB with integrated FOCS can reduce a substation’s footprint with over 50% compared to a conventional solution of live tank breakers with disconnectors and current transformers, due to reduced material and no additional insulation medium.[17]
Carbon dioxide (CO2) high-voltage
In 2012 ABB presented a 75 kV high-voltage breaker that uses carbon dioxide as the medium to extinguish the arc. The carbon dioxide breaker works on the same principles as an SF6 breaker and can also be produced as a disconnecting circuit breaker. By switching from SF6 to CO2 it is possible to reduce the CO2 emissions by 10 tons during the product’s life cycle.[18]
"Smart" circuit breakers
Several firms have looked at adding monitoring for appliances via electronics or using a digital circuit breaker to monitor the breakers remotely. Utility companies in the United States have been reviewing use of the technology to turn on and off appliances, as well as potentially turning off charging of electric cars during periods of high electrical grid load. These devices under research and testing would have wireless capability to monitor the electrical in a house via a smartphone app or other means.[19]
Atom Power, a company based in North Carolina, is also considering adopting "smart" circuit breakers for industrial applications, which may have greater benefits. Siemens has publicly said that the circuit breaker technology shows “great promise” for future applications.[19]
Other breakers

The following types are described in separate articles.
Breakers for protections against earth faults too small to trip an over-current device:
RCCB (Residual Current Operated Circuit-Breaker without Integral Overcurrent Protection) as a type of Residual-current device (RCD, formerly known as a residual current device) — detects current imbalance, but does not provide over-current protection. In the United States and Canada these are called ground fault circuit interrupters (GFCI).
Residual current breaker with over-current protection (RCBO) — combines the functions of an RCD and an MCB in one package. In the United States and Canada these are called GFCI breakers.
Earth leakage circuit breaker (ELCB) — This detects current in the earth wire directly rather than detecting imbalance. They are no longer seen in new installations as they cannot detect any dangerous condition where the current is returning to earth by another route - such as via a person on the ground or via plumbing. (also called VOELCB in the UK).
Recloser — A type of circuit breaker that closes automatically after a delay. These are used on overhead electric power distribution systems, to prevent short duration faults from causing sustained outages.
Polyswitch (polyfuse) — A small device commonly described as an automatically resetting fuse rather than a circuit breaker.
See also

Arc-fault circuit interrupter
Ring Main Unit
Circuit total limitation (CTL)
Distribution board (Circuit breaker panel)
Earthing system
Hybrid switchgear module
Insulation monitoring device
Motor control center (MCC)
Network protector
Power distribution center (PDC)
Power system protection
Remote racking system
Sulfur hexafluoride circuit breaker

General
BS EN 60898-1. Electrical accessories — Circuit breakers for over-current protection for household and similar installations. British Standards Institution, 2003.

When was the circuit breaker first developed?


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This is a list of leaders of Armenia from 1918 to the present. It includes leaders of the short-lived First Republic of Armenia (1918–1920), Soviet Armenia (1920–1991), and the post-Soviet government.
Leaders of Armenia (1918–present)
First Republic of Armenia (1918–1920)
Prime Minister of Armenia
Hovhannes Kajaznuni (30 June 1918 – 28 May 1919)
Alexander Khatisyan (28 May 1919 – 5 May 1920)
Hamazasp "Hamo" Ohanjanyan (5 May 1920 – 25 November 1920)
Simon Vratsian (25 November 1920 – 2 December 1920)
Transcaucasian Socialist Federative Soviet Republic (1922–1936) and Armenian Soviet Socialist Republic (1936–1991)
First Secretaries of the Communist Party of Armenia
Gevork Alikhanyan (December 1920 – April 1921)
Sargis Lukashin (April 1921 – 29 April 1922)
Askanaz Mravyan (29 April 1922 – March 1923)
Ashot Hovhannisyan (March 1923 – July 1927)
Haik Osepyan (July 1927 – April 1928)
Aykaz Kostanyan (April 1928 – 7 May 1930)
Aghasi Khanjian (7 May 1930 – 6 July 1936)
Amatuni Vartapetyan (13 July 1936 – 21 September 1937)
Grigory Arutyunov (24 September 1937 – November 1953)
Suren Tovmasyan (November 1953 – 28 December 1960)
Yakov Zarobyan (28 December 1960 – 5 February 1966)
Anton Kochinyan (5 February 1966 – 27 November 1974)
Karen Demirchyan (27 November 1974 – 21 May 1988)
Suren Arutyunyan (21 May 1988 – 6 April 1990)
Vladimir Movsisyan (6 April 1990 – 30 November 1990)
Stepan Pogosyan (30 November 1990 – 14 May 1991)
Aram Gaspar Sargsyan (14 May 1991 – 7 September 1991)
Chairman of the Supreme Council
Levon Ter-Petrossian (4 August 1990 - 11 November 1991)
Armenia (1991–present)
Presidents

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Based on new constitution of Armenia which came in force on 9 April 2018, the Presidential post became ceremonial and the main power resides on Prime Minister.


List of ''Everwood'' episodes

Everwood is an American television drama series that premiered on The WB on September 16, 2002. It ran for four seasons and ended on June 5, 2006 with 89 episodes produced. Each episode began with a traditional "previously on..." recap of prior events, which preceded the opening sequence, and most of the episodes were narrated by one character. The series' fourth and final season concluded with a two-hour finale.
Series overview

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