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Astrangia poculata, the northern star coral, is a temperate stony coral, widely documented along the eastern coast of the United States. The coral can live with and without zooxanthellae (algal symbionts), making it an ideal model organism to study microbial community interactions associated with symbiotic state. However, the ability to develop primers and probes to more specifically target key microbial groups has been hindered by the lack of full-length 16S rRNA sequences, since sequences produced by the Illumina platform are of insufficient length (approximately 250 base pairs) for the design of primers and probes. In 2019, Goldsmith et al. demonstrated Sanger sequencing was capable of reproducing the biologically relevant diversity detected by deeper next-generation sequencing, while also producing longer sequences useful to the research community for probe and primer design (see diagram on right).
Holobionts
Reef-building corals are well-studied holobionts that include the coral itself together with its symbiont zooxanthellae (photosynthetic dinoflagellates), as well as its associated bacteria and viruses. Co-evolutionary patterns exist for coral microbial communities and coral phylogeny.
It is known that the coral's microbiome and symbiont influence host health, however, the historic influence of each member on others is not well understood. Scleractinian corals have been diversifying for longer than many other symbiotic systems, and their microbiomes are known to be partially species-specific. It has been suggested that Endozoicomonas, a commonly highly abundant bacterium in corals, has exhibited codiversification with its host. This hints at an intricate set of relationships between the members of the coral holobiont that have been developing as evolution of these members occurs. | Coral | Wikipedia | 391 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
A study published in 2018 revealed evidence of phylosymbiosis between corals and their tissue and skeleton microbiomes. The coral skeleton, which represents the most diverse of the three coral microbiomes, showed the strongest evidence of phylosymbiosis. Coral microbiome composition and richness were found to reflect coral phylogeny. For example, interactions between bacterial and eukaryotic coral phylogeny influence the abundance of Endozoicomonas, a highly abundant bacterium in the coral holobiont. However, host-microbial cophylogeny appears to influence only a subset of coral-associated bacteria.
Reefs
Many corals in the order Scleractinia are hermatypic, meaning that they are involved in building reefs. Most such corals obtain some of their energy from zooxanthellae in the genus Symbiodinium. These are symbiotic photosynthetic dinoflagellates which require sunlight; reef-forming corals are therefore found mainly in shallow water. They secrete calcium carbonate to form hard skeletons that become the framework of the reef. However, not all reef-building corals in shallow water contain zooxanthellae, and some deep water species, living at depths to which light cannot penetrate, form reefs but do not harbour the symbionts.
There are various types of shallow-water coral reef, including fringing reefs, barrier reefs and atolls; most occur in tropical and subtropical seas. They are very slow-growing, adding perhaps one centimetre (0.4 in) in height each year. The Great Barrier Reef is thought to have been laid down about two million years ago. Over time, corals fragment and die, sand and rubble accumulates between the corals, and the shells of clams and other molluscs decay to form a gradually evolving calcium carbonate structure. Coral reefs are extremely diverse marine ecosystems hosting over 4,000 species of fish, massive numbers of cnidarians, molluscs, crustaceans, and many other animals.
Evolution | Coral | Wikipedia | 426 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
At certain times in the geological past, corals were very abundant. Like modern corals, their ancestors built reefs, some of which ended as great structures in sedimentary rocks. Fossils of fellow reef-dwellers algae, sponges, and the remains of many echinoids, brachiopods, bivalves, gastropods, and trilobites appear along with coral fossils. This makes some corals useful index fossils. Coral fossils are not restricted to reef remnants, and many solitary fossils are found elsewhere, such as Cyclocyathus, which occurs in England's Gault clay formation.
Early corals
Corals first appeared in the Cambrian about . Fossils are extremely rare until the Ordovician period, 100 million years later, when Heliolitida, rugose, and tabulate corals became widespread. Paleozoic corals often contained numerous endobiotic symbionts.
Tabulate corals occur in limestones and calcareous shales of the Ordovician period, with a gap in the fossil record due to extinction events at the end of the Ordovician. Corals reappeared some millions of years later during the Silurian period, and tabulate corals often form low cushions or branching masses of calcite alongside rugose corals. Tabulate coral numbers began to decline during the middle of the Silurian period.
Rugose or horn corals became dominant by the middle of the Silurian period, and during the Devonian, corals flourished with more than 200 genera. The rugose corals existed in solitary and colonial forms, and were also composed of calcite. Both rugose and tabulate corals became extinct in the Permian–Triassic extinction event (along with 85% of marine species), and there is a gap of tens of millions of years until new forms of coral evolved in the Triassic. | Coral | Wikipedia | 383 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Modern corals
The currently ubiquitous stony corals, Scleractinia, appeared in the Middle Triassic to fill the niche vacated by the extinct rugose and tabulate orders and is not closely related to the earlier forms. Unlike the corals prevalent before the Permian extinction, which formed skeletons of a form of calcium carbonate known as calcite, modern stony corals form skeletons composed of the aragonite. Their fossils are found in small numbers in rocks from the Triassic period, and become common in the Jurassic and later periods. Although they are geologically younger than the tabulate and rugose corals, the aragonite of their skeletons is less readily preserved, and their fossil record is accordingly less complete.
Status
Threats
Coral reefs are under stress around the world. In particular, coral mining, agricultural and urban runoff, pollution (organic and inorganic), overfishing, blast fishing, disease, and the digging of canals and access into islands and bays are localized threats to coral ecosystems. Broader threats are sea temperature rise, sea level rise and pH changes from ocean acidification, all associated with greenhouse gas emissions. In 1998, 16% of the world's reefs died as a result of increased water temperature.
Approximately 10% of the world's coral reefs are dead. About 60% of the world's reefs are at risk due to human-related activities. The threat to reef health is particularly strong in Southeast Asia, where 80% of reefs are endangered. Over 50% of the world's coral reefs may be destroyed by 2030; as a result, most nations protect them through environmental laws.
In the Caribbean and tropical Pacific, direct contact between ~40–70% of common seaweeds and coral causes bleaching and death to the coral via transfer of lipid-soluble metabolites. Seaweed and algae proliferate given adequate nutrients and limited grazing by herbivores such as parrotfish.
Water temperature changes of more than or salinity changes can kill some species of coral. Under such environmental stresses, corals expel their Symbiodinium; without them, coral tissues reveal the white of their skeletons, an event known as coral bleaching. | Coral | Wikipedia | 442 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Submarine springs found along the coast of Mexico's Yucatán Peninsula produce water with a naturally low pH (relatively high acidity) providing conditions similar to those expected to become widespread as the oceans absorb carbon dioxide. Surveys discovered multiple species of live coral that appeared to tolerate the acidity. The colonies were small and patchily distributed and had not formed structurally complex reefs such as those that compose the nearby Mesoamerican Barrier Reef System.
Coral health
To assess the threat level of coral, scientists developed a coral imbalance ratio, Log (Average abundance of disease-associated taxa / Average abundance of healthy associated taxa). The lower the ratio the healthier the microbial community is. This ratio was developed after the microbial mucus of coral was collected and studied.
Climate change impacts
Increasing sea surface temperatures in tropical regions (~) the last century have caused major coral bleaching, death, and therefore shrinking coral populations. Although coral are able to adapt and acclimate, it is uncertain if this evolutionary process will happen quickly enough to prevent major reduction of their numbers. Climate change causes more frequent and more severe storms that can destroy coral reefs.
Annual growth bands in some corals, such as the deep sea bamboo corals (Isididae), may be among the first signs of the effects of ocean acidification on marine life. The growth rings allow geologists to construct year-by-year chronologies, a form of incremental dating, which underlie high-resolution records of past climatic and environmental changes using geochemical techniques.
Certain species form communities called microatolls, which are colonies whose top is dead and mostly above the water line, but whose perimeter is mostly submerged and alive. Average tide level limits their height. By analyzing the various growth morphologies, microatolls offer a low-resolution record of sea level change. Fossilized microatolls can also be dated using radiocarbon dating. Such methods can help to reconstruct Holocene sea levels.
Though coral have large sexually-reproducing populations, their evolution can be slowed by abundant asexual reproduction. Gene flow is variable among coral species. According to the biogeography of coral species, gene flow cannot be counted on as a dependable source of adaptation as they are very stationary organisms. Also, coral longevity might factor into their adaptivity. | Coral | Wikipedia | 475 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
However, adaptation to climate change has been demonstrated in many cases, which is usually due to a shift in coral and zooxanthellae genotypes. These shifts in allele frequency have progressed toward more tolerant types of zooxanthellae. Scientists found that a certain scleractinian zooxanthella is becoming more common where sea temperature is high. Symbionts able to tolerate warmer water seem to photosynthesise more slowly, implying an evolutionary trade-off.
In the Gulf of Mexico, where sea temperatures are rising, cold-sensitive staghorn and elkhorn coral have shifted in location.
Not only have the symbionts and specific species been shown to shift, but there seems to be a certain growth rate favorable to selection. Slower-growing but more heat-tolerant corals have become more common. The changes in temperature and acclimation are complex. Some reefs in current shadows represent a refugium location that will help them adjust to the disparity in the environment even if eventually the temperatures may rise more quickly there than in other locations. This separation of populations by climatic barriers causes a realized niche to shrink greatly in comparison to the old fundamental niche.
Geochemistry
Corals are shallow, colonial organisms that integrate oxygen and trace elements into their skeletal aragonite (polymorph of calcite) crystalline structures as they grow. Geochemical anomalies within the crystalline structures of corals represent functions of temperature, salinity and oxygen isotopic composition. Such geochemical analysis can help with climate modeling. The ratio of oxygen-18 to oxygen-16 (δ18O), for example, is a proxy for temperature.
Strontium/calcium ratio anomaly
Time can be attributed to coral geochemistry anomalies by correlating strontium/calcium minimums with sea surface temperature (SST) maximums to data collected from NINO 3.4 SSTA. | Coral | Wikipedia | 392 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Oxygen isotope anomaly
The comparison of coral strontium/calcium minimums with sea surface temperature maximums, data recorded from NINO 3.4 SSTA, time can be correlated to coral strontium/calcium and δ18O variations. To confirm the accuracy of the annual relationship between Sr/Ca and δ18O variations, a perceptible association to annual coral growth rings confirms the age conversion. Geochronology is established by the blending of Sr/Ca data, growth rings, and stable isotope data. El Nino-Southern Oscillation (ENSO) is directly related to climate fluctuations that influence coral δ18O ratio from local salinity variations associated with the position of the South Pacific convergence zone (SPCZ) and can be used for ENSO modeling.
Sea surface temperature and sea surface salinity
The global moisture budget is primarily being influenced by tropical sea surface temperatures from the position of the Intertropical Convergence Zone (ITCZ). The Southern Hemisphere has a unique meteorological feature positioned in the southwestern Pacific Basin called the South Pacific Convergence Zone (SPCZ), which contains a perennial position within the Southern Hemisphere. During ENSO warm periods, the SPCZ reverses orientation extending from the equator down south through Solomon Islands, Vanuatu, Fiji and towards the French Polynesian Islands; and due east towards South America affecting geochemistry of corals in tropical regions.
Geochemical analysis of skeletal coral can be linked to sea surface salinity (SSS) and sea surface temperature (SST), from El Nino 3.4 SSTA data, of tropical oceans to seawater δ18O ratio anomalies from corals. ENSO phenomenon can be related to variations in sea surface salinity (SSS) and sea surface temperature (SST) that can help model tropical climate activities.
Limited climate research on current species
Climate research on live coral species is limited to a few studied species. Studying Porites coral provides a stable foundation for geochemical interpretations that is much simpler to physically extract data in comparison to Platygyra species where the complexity of Platygyra species skeletal structure creates difficulty when physically sampled, which happens to be one of the only multidecadal living coral records used for coral paleoclimate modeling.
Protection
Marine Protected Areas, Biosphere reserves, marine parks, national monuments world heritage status, fishery management and habitat protection can protect reefs from anthropogenic damage. | Coral | Wikipedia | 492 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Many governments now prohibit removal of coral from reefs, and inform coastal residents about reef protection and ecology. While local action such as habitat restoration and herbivore protection can reduce local damage, the longer-term threats of acidification, temperature change and sea-level rise remain a challenge.
Protecting networks of diverse and healthy reefs, not only climate refugia, helps ensure the greatest chance of genetic diversity, which is critical for coral to adapt to new climates. A variety of conservation methods applied across marine and terrestrial threatened ecosystems makes coral adaption more likely and effective.
To eliminate destruction of corals in their indigenous regions, projects have been started to grow corals in non-tropical countries.
Relation to humans
Local economies near major coral reefs benefit from an abundance of fish and other marine creatures as a food source. Reefs also provide recreational scuba diving and snorkeling tourism. These activities can damage coral but international projects such as Green Fins that encourage dive and snorkel centres to follow a Code of Conduct have been proven to mitigate these risks.
Jewelry
Corals' many colors give it appeal for necklaces and other jewelry. Intensely red coral is prized as a gemstone. Sometimes called fire coral, it is not the same as fire coral. Red coral is very rare because of overharvesting. In general, it is inadvisable to give coral as gifts since they are in decline from stressors like climate change, pollution, and unsustainable fishing.
Always considered a precious mineral, "the Chinese have long associated red coral with auspiciousness and longevity because of its color and its resemblance to deer antlers (so by association, virtue, long life, and high rank". It reached its height of popularity during the Manchu or Qing Dynasty (1644–1911) when it was almost exclusively reserved for the emperor's use either in the form of coral beads (often combined with pearls) for court jewelry or as decorative Penjing (decorative miniature mineral trees). Coral was known as shanhu in Chinese. The "early-modern 'coral network' [began in] the Mediterranean Sea [and found its way] to Qing China via the English East India Company". There were strict rules regarding its use in a code established by the Qianlong Emperor in 1759.
Medicine | Coral | Wikipedia | 464 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
In medicine, chemical compounds from corals can potentially be used to treat cancer, neurological diseases, inflammation including arthritis, pain, bone loss, high blood pressure and for other therapeutic uses. Coral skeletons, e.g. Isididae are being researched for their potential near-future use for bone grafting in humans.
Coral Calx, known as Praval Bhasma in Sanskrit, is widely used in traditional system of Indian medicine as a supplement in the treatment of a variety of bone metabolic disorders associated with calcium deficiency. In classical times ingestion of pulverized coral, which consists mainly of the weak base calcium carbonate, was recommended for calming stomach ulcers by Galen and Dioscorides.
Construction
Coral reefs in places such as the East African coast are used as a source of building material. Ancient (fossil) coral limestone, notably including the Coral Rag Formation of the hills around Oxford (England), was once used as a building stone, and can be seen in some of the oldest buildings in that city including the Saxon tower of St Michael at the Northgate, St. George's Tower of Oxford Castle, and the medieval walls of the city.
Shoreline protection
Healthy coral reefs absorb 97 percent of a wave's energy, which buffers shorelines from currents, waves, and storms, helping to prevent loss of life and property damage. Coastlines protected by coral reefs are also more stable in terms of erosion than those without.
Local economies
Coastal communities near coral reefs rely heavily on them. Worldwide, more than 500 million people depend on coral reefs for food, income, coastal protection, and more. The total economic value of coral reef services in the United States – including fisheries, tourism, and coastal protection – is more than $3.4 billion a year.
Aquaria
The saltwater fishkeeping hobby has expanded, over recent years, to include reef tanks, fish tanks that include large amounts of live rock on which coral is allowed to grow and spread. These tanks are either kept in a natural-like state, with algae (sometimes in the form of an algae scrubber) and a deep sand bed providing filtration, or as "show tanks", with the rock kept largely bare of the algae and microfauna that would normally populate it, in order to appear neat and clean. | Coral | Wikipedia | 469 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
The most popular kind of coral kept is soft coral, especially zoanthids and mushroom corals, which are especially easy to grow and propagate in a wide variety of conditions, because they originate in enclosed parts of reefs where water conditions vary and lighting may be less reliable and direct. More serious fishkeepers may keep small polyp stony coral, which is from open, brightly lit reef conditions and therefore much more demanding, while large polyp stony coral is a sort of compromise between the two.
Aquaculture
Coral aquaculture, also known as coral farming or coral gardening, is the cultivation of corals for commercial purposes or coral reef restoration. Aquaculture is showing promise as a potentially effective tool for restoring coral reefs, which have been declining around the world. The process bypasses the early growth stages of corals when they are most at risk of dying. Coral fragments known as "seeds" are grown in nurseries then replanted on the reef. Coral is farmed by coral farmers who live locally to the reefs and farm for reef conservation or for income. It is also farmed by scientists for research, by businesses for the supply of the live and ornamental coral trade and by private aquarium hobbyists.
Gallery
Further images: commons:Category:Coral reefs and commons:Category:Corals | Coral | Wikipedia | 262 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
A cotton gin—meaning "cotton engine"—is a machine that quickly and easily separates cotton fibers from their seeds, enabling much greater productivity than manual cotton separation. The separated seeds may be used to grow more cotton or to produce cottonseed oil.
Handheld roller gins had been used in the Indian subcontinent since at earliest AD 500 and then in other regions. The Indian worm-gear roller gin was invented sometime around the 16th century and has, according to Lakwete, remained virtually unchanged up to the present time. A modern mechanical cotton gin was created by American inventor Eli Whitney in 1793 and patented in 1794.
Whitney's gin used a combination of a wire screen and small wire hooks to pull the cotton through, while brushes continuously removed the loose cotton lint to prevent jams. It revolutionized the cotton industry in the United States, but also inadvertently led to the growth of slavery in the American South. Whitney's gin made cotton farming more profitable and efficient so plantation owners expanded their plantations and used more of their slaves to pick cotton. Whitney never invented the machine to harvest cotton: it still had to be picked by hand. The invention has thus been identified as an inadvertent contributing factor to the outbreak of the American Civil War. Modern automated cotton gins use multiple powered cleaning cylinders and saws, and offer far higher productivity than their hand-powered precursors.
Purpose
Cotton fibers are produced in the seed pods ("bolls") of the cotton plant where the fibers ("lint") in the bolls are tightly interwoven with seeds. To make the fibers usable, the seeds and fibers must first be separated, a task which had been previously performed manually, with production of cotton requiring hours of labor for the separation. Many simple seed-removing devices had been invented, but until the innovation of the cotton gin, most required significant operator attention and worked only on a small scale.
Mechanism | Cotton gin | Wikipedia | 389 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
Whitney's gin is made with two rotating cylinders. The first cylinder has lines of teeth around the circumference, and angled against this cylinder is a metal plate with small holes, "ginning ribs", through which the teeth can fit with minimal gaps. The teeth grip the cotton fibers as the mechanism rotates, dragging them through these small holes. The seeds are too big to fit through the holes, and are thus removed from the rotating cotton by the metal plate, before they fall into a collecting pot. On the other side of the first cylinder, there is a second cylinder, also rotating, with brushes attached. This second cylinder wipes the cotton from the first, and deposits it into the collecting bucket.
The seed is reused for planting or is sent to an oil mill to be further processed into cottonseed oil and cottonseed meal. The lint cleaners again use saws and grid bars, this time to separate immature seeds and any remaining foreign matter from the fibers. The bale press then compresses the cotton into bales for storage and shipping. Modern gins can process up to 15 tonnes (33,000 lb) of cotton per hour.
History
A single-roller cotton gin came into use in India by the 5th century. An improvement invented in India was the two-roller gin, known as the "churka", "charki", or "wooden-worm-worked roller".
Early cotton gins
The earliest versions of the cotton gin consisted of a single roller made of iron or wood and a flat piece of stone or wood. The earliest evidence of the cotton gin is found in the fifth century, in the form of Buddhist paintings depicting a single-roller gin in the Ajanta Caves in western India. These early gins were difficult to use and required a great deal of skill. A narrow single roller was necessary to expel the seeds from the cotton without crushing the seeds. The design was similar to that of a mealing stone, which was used to grind grain. The early history of the cotton gin is ambiguous, because archeologists likely mistook the cotton gin's parts for other tools.
Medieval and Early Modern India
Between the 12th and 14th centuries, dual-roller gins appeared in India and China. The Indian version of the dual-roller gin was prevalent throughout the Mediterranean cotton trade by the 16th century. This mechanical device was, in some areas, driven by waterpower. | Cotton gin | Wikipedia | 496 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
The worm gear roller gin, which was invented in the Indian subcontinent during the early Delhi Sultanate era of the 13th to 14th centuries, came into use in the Mughal Empire sometime around the 16th century, and is still used in the Indian subcontinent through to the present day. Another innovation, the incorporation of the crank handle in the cotton gin, first appeared sometime during the late Delhi Sultanate or the early Mughal Empire. The incorporation of the worm gear and crank handle into the roller cotton gin led to greatly expanded Indian cotton textile production during the Mughal era.
It was reported that, with an Indian cotton gin, which is half machine and half tool, one man and one woman could clean 28 pounds of cotton per day. With a modified Forbes version, one man and a boy could produce 250 pounds per day. If oxen were used to power 16 of these machines, and a few people's labor was used to feed them, they could produce as much work as 750 people did formerly.
United States
The Indian roller cotton gin, known as the churka or charkha, was introduced to the United States in the mid-18th century, when it was adopted in the southern United States. The device was adopted for cleaning long-staple cotton but was not suitable for the short-staple cotton that was more common in certain states such as Georgia. Several modifications were made to the Indian roller gin by Mr. Krebs in 1772 and Joseph Eve in 1788, but their uses remained limited to the long-staple variety, up until Eli Whitney's development of a short-staple cotton gin in 1793.
Eli Whitney's patent
Eli Whitney (1765–1825) applied for a patent of his cotton gin on October 28, 1793; the patent was granted on March 14, 1794, but was not validated until 1807. Whitney's patent was assigned patent number 72X. There is slight controversy over whether the idea of the modern cotton gin and its constituent elements are correctly attributed to Eli Whitney. The popular image of Whitney inventing the cotton gin is attributed to an article on the subject written in the early 1870s and later reprinted in 1910 in The Library of Southern Literature. In this article, the author claimed Catharine Littlefield Greene suggested to Whitney the use of a brush-like component instrumental in separating out the seeds and cotton. Greene's alleged role in the invention of the gin has not been verified independently. | Cotton gin | Wikipedia | 483 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
Whitney's cotton gin model was capable of cleaning of lint per day. The model consisted of a wooden cylinder covered by rows of slender wires which caught the fibers of the cotton bolls. Each row of wires then passed through the bars of a comb-like grid, pulling the cotton fibers through the grid as they did. The comb-like teeth of the grids were closely spaced, preventing the seeds, fragments of the hard dried calyx of the original cotton flower, or sticks and other debris attached to the fibers from passing through. A series of brushes on a second rotating cylinder then brushed the now-cleaned fibers loose from the wires, preventing the mechanism from jamming.
Many contemporary inventors attempted to develop a design that would process short staple cotton, and Hodgen Holmes, Robert Watkins, William Longstreet, and John Murray had all been issued patents for improvements to the cotton gin by 1796. However, the evidence indicates Whitney did invent the saw gin, for which he is famous. Although he spent many years in court attempting to enforce his patent against planters who made unauthorized copies, a change in patent law ultimately made his claim legally enforceable – too late for him to make much money from the device in the single year remaining before the patent expired. | Cotton gin | Wikipedia | 257 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
McCarthy's gin
While Whitney's gin facilitated the cleaning of seeds from short-staple cotton, it damaged the fibers of extra-long staple cotton (Gossypium barbadense). In 1840 Fones McCarthy received a patent for a "Smooth Cylinder Cotton-gin", a roller gin. McCarthy's gin was marketed for use with both short-staple and extra-long staple cotton but was particularly useful for processing long-staple cotton. After McCarthy's patent expired in 1861, McCarthy type gins were manufactured in Britain and sold around the world. McCarthy's gin was adopted for cleaning the Sea Island variety of extra-long staple cotton grown in Florida, Georgia and South Carolina. It cleaned cotton several times faster than the older gins, and, when powered by one horse, produced 150 to 200 pounds of lint a day. The McCarthy gin used a reciprocating knife to detach seed from the lint. Vibration caused by the reciprocating motion limited the speed at which the gin could operate. In the middle of the 20th Century gins using a rotating blade replaced ones using a reciprocating blade. These descendants of the McCarthy gin are the only gins now used for extra-long staple cotton in the United States.
Munger system gin
For a decade and a half after the end of the Civil War in 1865, a number of innovative features became widely used for ginning in the United States. They included steam power instead of animal power, an automatic feeder to assure that the gin stand ran smoothly, a condenser to make the clean cotton coming out of the gin easier to handle, and indoor presses so that cotton no longer had to be carried across the gin yard to be baled. Then, in 1879, while he was running his father's gin in Rutersville, Texas, Robert S. Munger invented additional system ginning techniques. Robert and his wife, Mary Collett, later moved to Mexia, Texas, built a system gin, and obtained related patents.
The Munger System Ginning Outfit (or system gin) integrated all the ginning operation machinery, thus assuring the cotton would flow through the machines smoothly. Such system gins use air to move cotton from machine to machine. Munger's motivation for his inventions included improving employee working conditions in the gin. However, the selling point for most gin owners was the accompanying cost savings while producing cotton both more speedily and of higher quality. | Cotton gin | Wikipedia | 503 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
By the 1960s, many other advances had been made in ginning machinery, but the manner in which cotton flowed through the gin machinery continued to be the Munger system.
Economic Historian William H. Phillips referred to the development of system ginning as "The Munger Revolution" in cotton ginning. He wrote,
"The Munger innovations were the culmination of what geographer Charles S. Aiken has termed the second ginning revolution, in which the privately owned plantation gins were replaced by large-scale public ginneries. This revolution, in turn, led to a major restructuring of the cotton gin industry, as the small, scattered gin factories and shops of the nineteenth century gave way to a dwindling number of large twentieth-century corporations designing and constructing entire ginning operations."
One of the few (and perhaps only) examples of a Munger gin left in existence is on display at Frogmore Plantation in Louisiana.
Effects in the United States
Prior to the introduction of the mechanical cotton gin, cotton had required considerable labor to clean and separate the fibers from the seeds. With Eli Whitney's gin, cotton became a tremendously profitable business, creating many fortunes in the Antebellum South. Cities such as New Orleans, Louisiana; Mobile, Alabama; Charleston, South Carolina; and Galveston, Texas became major shipping ports, deriving substantial economic benefit from cotton raised throughout the South. Additionally, the greatly expanded supply of cotton created strong demand for textile machinery and improved machine designs that replaced wooden parts with metal. This led to the invention of many machine tools in the early 19th century. | Cotton gin | Wikipedia | 324 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
The invention of the cotton gin caused massive growth in the production of cotton in the United States, concentrated mostly in the South. Cotton production expanded from 750,000 bales in 1830 to 2.85 million bales in 1850. As a result, the region became even more dependent on plantations that used black slave labor, with plantation agriculture becoming the largest sector of its economy. While it took a single laborer about ten hours to separate a single pound of fiber from the seeds, a team of two or three slaves using a cotton gin could produce around fifty pounds of cotton in just one day. The number of slaves rose in concert with the increase in cotton production, increasing from around 700,000 in 1790 to around 3.2 million in 1850. The invention of the cotton gin led to increased demands for slave labor in the American South, reversing the economic decline that had occurred in the region during the late 18th century. The cotton gin thus "transformed cotton as a crop and the American South into the globe's first agricultural powerhouse".
The invention of the cotton gin led to an increase in the use of slaves on Southern plantations. Because of that inadvertent effect on American slavery, which ensured that the South's economy developed in the direction of plantation-based agriculture (while encouraging the growth of the textile industry elsewhere, such as in the North), the invention of the cotton gin is frequently cited as one of the indirect causes of the American Civil War.
Modern cotton gins
In modern cotton production, cotton arrives at industrial cotton gins either in trailers, in compressed rectangular "modules" weighing up to 10 metric tons each or in polyethylene wrapped round modules similar to a bale of hay produced during the picking process by the most recent generation of cotton pickers. Trailer cotton (i.e. cotton not compressed into modules) arriving at the gin is sucked in via a pipe, approximately in diameter, that is swung over the cotton. This pipe is usually manually operated but is increasingly automated in modern cotton plants. The need for trailers to haul the product to the gin has been drastically reduced since the introduction of modules. If the cotton is shipped in modules, the module feeder breaks the modules apart using spiked rollers and extracts the largest pieces of foreign material from the cotton. The module feeder's loose cotton is then sucked into the same starting point as the trailer cotton. | Cotton gin | Wikipedia | 483 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
The cotton then enters a dryer, which removes excess moisture. The cylinder cleaner uses six or seven rotating, spiked cylinders to break up large clumps of cotton. Finer foreign material, such as soil and leaves, passes through rods or screens for removal. The stick machine uses centrifugal force to remove larger foreign matter, such as sticks and burrs, while the cotton is held by rapidly rotating saw cylinders.
The gin stand uses the teeth of rotating saws to pull the cotton through a series of "ginning ribs", which pull the fibers from the seeds which are too large to pass through the ribs. The cleaned seed is then removed from the gin via an auger conveyor system. The seed is reused for planting or is sent to an oil mill to be further processed into cottonseed oil and cottonseed meal. The lint cleaners again use saws and grid bars, this time to separate immature seeds and any remaining foreign matter from the fibers. The bale press then compresses the cotton into bales for storage and shipping. Modern gins can process up to of cotton per hour.
Modern cotton gins create a substantial amount of cotton gin residue (CGR) consisting of sticks, leaves, dirt, immature bolls, and cottonseed. Research is currently under way to investigate the use of this waste in producing ethanol. Due to fluctuations in the chemical composition in processing, there is difficulty in creating a consistent ethanol process, but there is potential to further maximize the utilization of waste in cotton production. | Cotton gin | Wikipedia | 313 | 47710 | https://en.wikipedia.org/wiki/Cotton%20gin | Technology | Farm and garden machinery | null |
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.
The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.
Direct current may be converted from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter.
Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.
History
Direct current was produced in 1800 by Italian physicist Alessandro Volta's battery, his Voltaic pile. The nature of how current flowed was not yet understood. French physicist André-Marie Ampère conjectured that current travelled in one direction from positive to negative. When French instrument maker Hippolyte Pixii built the first dynamo electric generator in 1832, he found that as the magnet used passed the loops of wire each half turn, it caused the flow of electricity to reverse, generating an alternating current. At Ampère's suggestion, Pixii later added a commutator, a type of "switch" where contacts on the shaft work with "brush" contacts to produce direct current. | Direct current | Wikipedia | 409 | 47713 | https://en.wikipedia.org/wiki/Direct%20current | Physical sciences | Electrical circuits | null |
The late 1870s and early 1880s saw electricity starting to be generated at power stations. These were initially set up to power arc lighting (a popular type of street lighting) running on very high voltage (usually higher than 3,000 volts) direct current or alternating current. This was followed by the widespread use of low voltage direct current for indoor electric lighting in business and homes after inventor Thomas Edison launched his incandescent bulb based electric "utility" in 1882. Because of the significant advantages of alternating current over direct current in using transformers to raise and lower voltages to allow much longer transmission distances, direct current was replaced over the next few decades by alternating current in power delivery. In the mid-1950s, high-voltage direct current transmission was developed, and is now an option instead of long-distance high voltage alternating current systems. For long distance undersea cables (e.g. between countries, such as NorNed), this DC option is the only technically feasible option. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct current.
Various definitions
The term DC is used to refer to power systems that use only one electrical polarity of voltage or current, and to refer to the constant, zero-frequency, or slowly varying local mean value of a voltage or current. For example, the voltage across a DC voltage source is constant as is the current through a direct current source. The DC solution of an electric circuit is the solution where all voltages and currents are constant. Any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero-mean time-varying component; the DC component is defined to be the expected value, or the average value of the voltage or current over all time.
Although DC stands for "direct current", DC often refers to "constant polarity". Under this definition, DC voltages can vary in time, as seen in the raw output of a rectifier or the fluctuating voice signal on a telephone line.
Some forms of DC (such as that produced by a voltage regulator) have almost no variations in voltage, but may still have variations in output power and current. | Direct current | Wikipedia | 461 | 47713 | https://en.wikipedia.org/wiki/Direct%20current | Physical sciences | Electrical circuits | null |
Circuits
A direct current circuit is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, and resistors. In this case, the circuit voltages and currents are independent of time. A particular circuit voltage or current does not depend on the past value of any circuit voltage or current. This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives with respect to time.
If a capacitor or inductor is added to a DC circuit, the resulting circuit is not, strictly speaking, a DC circuit. However, most such circuits have a DC solution. This solution gives the circuit voltages and currents when the circuit is in DC steady state. Such a circuit is represented by a system of differential equations. The solution to these equations usually contain a time varying or transient part as well as constant or steady state part. It is this steady state part that is the DC solution. There are some circuits that do not have a DC solution. Two simple examples are a constant current source connected to a capacitor and a constant voltage source connected to an inductor.
In electronics, it is common to refer to a circuit that is powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit even though what is meant is that the circuit is DC powered.
In a DC circuit, a power source (e.g. a battery, capacitor, etc.) has a positive and negative terminal, and likewise, the load also has a positive and negative terminal. To complete the circuit, positive charges need to flow from the power source to the load. The charges will then return to the negative terminal of the load, which will then flow back to the negative terminal of the battery, completing the circuit. If either the positive or negative terminal is disconnected, the circuit will not be complete and the charges will not flow.
In some DC circuit applications, polarity does not matter, which means you can connect positive and negative backwards and the circuit will still be complete and the load will still function normally. However, in most DC applications, polarity does matter, and connecting the circuit backwards will result in the load not working properly.
Applications
Domestic and commercial buildings
DC is commonly found in many extra-low voltage applications and some low-voltage applications, especially where these are powered by batteries or solar power systems (since both can produce only DC).
Most electronic circuits or devices require a DC power supply. | Direct current | Wikipedia | 505 | 47713 | https://en.wikipedia.org/wiki/Direct%20current | Physical sciences | Electrical circuits | null |
Domestic DC installations usually have different types of sockets, connectors, switches, and fixtures from those suitable for alternating current. This is mostly due to the lower voltages used, resulting in higher currents to produce the same amount of power.
It is usually important with a DC appliance to observe polarity, unless the device has a diode bridge to correct for this.
Automotive
Most automotive applications use DC. An automotive battery provides power for engine starting, lighting, the ignition system, the climate controls, and the infotainment system among others. The alternator is an AC device which uses a rectifier to produce DC for battery charging. Most highway passenger vehicles use nominally 12 V systems. Many heavy trucks, farm equipment, or earth moving equipment with Diesel engines use 24 volt systems. In some older vehicles, 6 V was used, such as in the original classic Volkswagen Beetle. At one point a 42 V electrical system was considered for automobiles, but this found little use. To save weight and wire, often the metal frame of the vehicle is connected to one pole of the battery and used as the return conductor in a circuit. Often the negative pole is the chassis "ground" connection, but positive ground may be used in some wheeled or marine vehicles.
In a battery electric vehicle, there are usually two separate DC systems. The "low voltage" DC system typically operates at 12V, and serves the same purpose as in an internal combustion engine vehicle. The "high voltage" system operates at 300-400V (depending on the vehicle), and provides the power for the traction motors. Increasing the voltage for the traction motors reduces the current flowing through them, increasing efficiency.
Telecommunication
Telephone exchange communication equipment uses standard −48 V DC power supply. The negative polarity is achieved by grounding the positive terminal of power supply system and the battery bank. This is done to prevent electrolysis depositions. Telephone installations have a battery system to ensure power is maintained for subscriber lines during power interruptions.
Other devices may be powered from the telecommunications DC system using a DC-DC converter to provide any convenient voltage.
Many telephones connect to a twisted pair of wires, and use a bias tee to internally separate the AC component of the voltage between the two wires (the audio signal) from the DC component of the voltage between the two wires (used to power the phone).
High-voltage power transmission | Direct current | Wikipedia | 487 | 47713 | https://en.wikipedia.org/wiki/Direct%20current | Physical sciences | Electrical circuits | null |
High-voltage direct current (HVDC) electric power transmission systems use DC for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses.
Other
Applications using fuel cells (mixing hydrogen and oxygen together with a catalyst to produce electricity and water as byproducts) also produce only DC.
Light aircraft electrical systems are typically 12 V or 24 V DC similar to automobiles. | Direct current | Wikipedia | 100 | 47713 | https://en.wikipedia.org/wiki/Direct%20current | Physical sciences | Electrical circuits | null |
A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems. Most HVDC links use voltages between 100 kV and 800 kV.
HVDC lines are commonly used for long-distance power transmission, since they require fewer conductors and incur less power loss than equivalent AC lines. HVDC also allows power transmission between AC transmission systems that are not synchronized. Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC also allows the transfer of power between grid systems running at different frequencies, such as 50 and 60 Hz. This improves the stability and economy of each grid, by allowing the exchange of power between previously incompatible networks.
The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden (ASEA) and in Germany. Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, and a 100 kV, 20 MW system between Gotland and mainland Sweden in 1954. Before the Chinese project of 2019, the longest HVDC link in the world was the Rio Madeira link in Brazil, which consists of two bipoles of ±600 kV, 3150 MW each, connecting Porto Velho in the state of Rondônia to the São Paulo area with a length of more than .
High voltage transmission
High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current:
Since the energy lost as heat in the wires is directly proportional to the square of the current using half the current at double the voltage reduces the line losses by a factor of 4. While energy lost in transmission can also be reduced by decreasing the resistance by increasing the conductor size, larger conductors are heavier and more expensive.
High voltage cannot readily be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment. Transformers are used to change the voltage levels in alternating current (AC) transmission circuits, but cannot pass DC current. Transformers made AC voltage changes practical, and AC generators were more efficient than those using DC. These advantages led to early low-voltage DC transmission systems being supplanted by AC systems around the turn of the 20th century. | High-voltage direct current | Wikipedia | 510 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Practical conversion of current between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, power semiconductor devices including thyristors, integrated gate-commutated thyristors (IGCTs), MOS-controlled thyristors (MCTs) and insulated-gate bipolar transistors (IGBT).
History
Electromechanical systems
The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission, but only 1.5 kW was transmitted. An early method of HVDC transmission was developed by the Swiss engineer René Thury and his method, the Thury system, was put into practice by 1889 in Italy by the Acquedotto De Ferrari-Galliera company. This system used series-connected motor-generator sets to increase the voltage. Each set was insulated from electrical ground and driven by insulated shafts from a prime mover. The transmission line was operated in a constant-current mode, with up to 5,000 volts across each machine, some machines having double commutators to reduce the voltage on each commutator. This system transmitted 630 kW at 14 kV DC over a distance of . The Moutiers–Lyon system transmitted 8,600 kW of hydroelectric power a distance of , including of underground cable. This system used eight series-connected generators with dual commutators for a total voltage of 150 kV between the positive and negative poles, and operated from 1906 until 1936. Fifteen Thury systems were in operation by 1913. Other Thury systems operating at up to 100 kV DC worked into the 1930s, but the rotating machinery required high maintenance and had high energy loss.
Various other electromechanical devices were tested during the first half of the 20th century with little commercial success. One technique attempted for conversion of direct current from a high transmission voltage to lower utilization voltage was to charge series-connected batteries, then reconnect the batteries in parallel to serve distribution loads. While at least two commercial installations were tried around the turn of the 20th century, the technique was not generally useful owing to the limited capacity of batteries, difficulties in switching between series and parallel configurations, and the inherent energy inefficiency of a battery charge/discharge cycle. | High-voltage direct current | Wikipedia | 469 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Mercury arc valves
First proposed in 1914, the grid controlled mercury-arc valve became available during the period 1920 to 1940 for the rectifier and inverter functions associated with DC transmission. Starting in 1932, General Electric tested mercury-vapor valves and a 12 kV DC transmission line, which also served to convert 40 Hz generation to serve 60 Hz loads, at Mechanicville, New York. In 1941, a 60 MW, ±200 kV, buried cable link, known as the Elbe-Project, was designed for the city of Berlin using mercury arc valves but, owing to the collapse of the German government in 1945, the project was never completed. The nominal justification for the project was that, during wartime, a buried cable would be less conspicuous as a bombing target. The equipment was moved to the Soviet Union and was put into service there as the Moscow–Kashira HVDC system. The Moscow–Kashira system and the 1954 connection by Uno Lamm's group at ASEA between the mainland of Sweden and the island of Gotland marked the beginning of the modern era of HVDC transmission.
Mercury arc valves were common in systems designed up to 1972, the last mercury arc HVDC system (the Nelson River Bipole 1 system in Manitoba, Canada) having been put into service in stages between 1972 and 1977. Since then, all mercury arc systems have been either shut down or converted to use solid-state devices. The last HVDC system to use mercury arc valves was the Inter-Island HVDC link between the North and South Islands of New Zealand, which used them on one of its two poles. The mercury arc valves were decommissioned on 1 August 2012, ahead of the commissioning of replacement thyristor converters.
Thyristor valves
The development of thyristor valves for HVDC began in the late 1960s. The first complete HVDC scheme based on thyristor was the Eel River scheme in Canada, which was built by General Electric and went into service in 1972.
Since 1977, new HVDC systems have used solid-state devices, in most cases thyristors. Like mercury arc valves, thyristors require connection to an external AC circuit in HVDC applications to turn them on and off. HVDC using thyristors is also known as line-commutated converter (LCC) HVDC. | High-voltage direct current | Wikipedia | 485 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
On March 15, 1979, a 1920 MW thyristor based direct current connection between Cabora Bassa and Johannesburg () was energized. The conversion equipment was built in 1974 by Allgemeine Elektricitäts-Gesellschaft AG (AEG), and Brown, Boveri & Cie (BBC) and Siemens were partners in the project. Service interruptions of several years were a result of a civil war in Mozambique. The transmission voltage of ±533 kV was the highest in the world at the time.
Capacitor-commutated converters
Line-commutated converters have some limitations in their use for HVDC systems. This results from requiring a period of reverse voltage to affect the turn off. An attempt to address these limitations is the capacitor-commutated converter (CCC). The CCC has series capacitors inserted into the AC line connections. CCC has remained only a niche application because of the advent of voltage-source converters (VSCs) which more directly address turn-off issues.
Voltage-source converters
Widely used in motor drives since the 1980s, voltage-source converters (VSCs) started to appear in HVDC in 1997 with the experimental Hellsjön–Grängesberg project in Sweden. By the end of 2011, this technology had captured a significant proportion of the HVDC market. | High-voltage direct current | Wikipedia | 286 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
The development of higher rated insulated-gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs), and integrated gate-commutated thyristors (IGCTs), has made HVDC systems more economical and reliable. This is because modern IGBTs incorporate a short-circuit failure mode, wherein should an IGBT fail, it is mechanically shorted. Therefore, modern VSC HVDC converter stations are designed with sufficient redundancy to guarantee operation over their entire service lives. The manufacturer ABB Group calls this concept HVDC Light, while Siemens calls a similar concept HVDC PLUS (Power Link Universal System) and Alstom call their product based upon this technology HVDC MaxSine. They have extended the use of HVDC down to blocks as small as a few tens of megawatts and overhead lines as short as a few dozen kilometers. There are several different variants of VSC technology: most installations built until 2012 use pulse-width modulation in a circuit that is effectively an ultra-high-voltage motor drive. More recent installations, including HVDC PLUS and HVDC MaxSine, are based on variants of a converter called a Modular Multilevel Converter (MMC).
Multilevel converters have the advantage that they allow harmonic filtering equipment to be reduced or eliminated altogether. By way of comparison, AC harmonic filters of typical line-commutated converter stations cover nearly half of the converter station area.
With time, voltage-source converter systems will probably replace all installed simple thyristor-based systems, including the highest DC power transmission applications.
Comparison with AC
Advantages
A long-distance, point-to-point HVDC transmission scheme generally has lower overall investment cost and lower losses than an equivalent AC transmission scheme. Although HVDC conversion equipment at the terminal stations is costly, the total DC transmission-line costs over long distances are lower than for an AC line of the same distance. HVDC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect. AC systems use a higher peak voltage for the same power, increasing insulator costs. | High-voltage direct current | Wikipedia | 462 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Depending on voltage level and construction details, HVDC transmission losses are quoted at 3.5% per , about 50% less than AC (6.7%) lines at the same voltage. This is because direct current transfers only active power and thus causes lower losses than alternating current, which transfers both active and reactive power. In other words, transmitting electric AC power over long distances inevitably results in a phase shift between voltage and current. Because of this phase shift the effective Power=Current*Voltage, where * designates a vector product, decreases. Since DC power has no phase, the phase shift cannot occur in the DC case.
HVDC transmission may also be selected for other technical benefits. HVDC can transfer power between separate AC networks. HVDC power flow between separate AC systems can be automatically controlled to support either network during transient conditions, but without the risk that a major power-system collapse in one network will lead to a collapse in the second. The controllability feature is also useful where control of energy trading is needed.
Specific applications where HVDC transmission technology provides benefits include:
Undersea-cable transmission schemes (e.g. the North Sea Link, the NorNed cable between Norway and the Netherlands, Italy's SAPEI cable between Sardinia and the mainland, the Basslink between the Australian mainland and Tasmania, and the Baltic Cable between Sweden and Germany).
Endpoint-to-endpoint long-haul bulk power transmission without intermediate taps, usually to connect a remote generating plant to the main grid (e.g. the Nelson River DC Transmission System in Canada).
Increasing the capacity of an existing transmission line in situations where additional wires are difficult or expensive to install.
Power transmission and stabilization between unsynchronized AC networks, with the extreme example being an ability to transfer power between countries that use AC at different frequencies.
Stabilizing a predominantly AC power grid, without increasing prospective short-circuit current.
Integration of renewable resources such as wind into the main transmission grid. HVDC overhead lines for onshore wind integration projects and HVDC cables for offshore projects have been proposed in North America and Europe for both technical and economic reasons. DC grids with multiple VSCs are one of the technical solutions for pooling offshore wind energy and transmitting it to load centers located far away onshore. | High-voltage direct current | Wikipedia | 472 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Cable systems
Long undersea or underground high-voltage cables have a high electrical capacitance compared with overhead transmission lines since the live conductors within the cable are surrounded by a relatively thin layer of insulation (the dielectric), and a metal sheath. The geometry is that of a long coaxial capacitor. The total capacitance increases with the length of the cable. This capacitance is in a parallel circuit with the load. Where alternating current is used for cable transmission, additional current must flow in the cable to charge this cable capacitance. Another way to look at this is to realize, that such capacitance causes a phase shift between voltage and current, and thus decrease of the transmitted power, which is a vector product of voltage and current. Additional energy losses also occur as a result of dielectric losses in the cable insulation. For a sufficiently long AC cable, the entire current-carrying ability of the conductor would be needed to supply the charging current alone. This cable capacitance issue limits the length and power-carrying ability of AC power cables.
However, if direct current is used, the cable capacitance is charged only when the cable is first energized or if the voltage level changes; there is no additional current required. DC powered cables are limited only by their temperature rise and Ohm's law. Although some leakage current flows through the dielectric insulator, this effect is also present in AC systems and is small compared to the cable's rated current.
Overhead line systems
The capacitive effect of long underground or undersea cables in AC transmission applications also applies to AC overhead lines, although to a much lesser extent. Nevertheless, for a long AC overhead transmission line, the current flowing just to charge the line capacitance can be significant, and this reduces the capability of the line to carry useful current to the load at the remote end. Another factor that reduces the useful current-carrying ability of AC lines is the skin effect, which causes a nonuniform distribution of current over the cross-sectional area of the conductor. Transmission line conductors operating with direct current suffer from neither constraint. Therefore, for the same conductor losses (or heating effect), a given conductor can carry more power to the load when operating with HVDC than AC. | High-voltage direct current | Wikipedia | 477 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Finally, depending upon the environmental conditions and the performance of overhead line insulation operating with HVDC, it may be possible for a given transmission line to operate with a constant HVDC voltage that is approximately the same as the peak AC voltage for which it is designed and insulated. The power delivered in an AC system is defined by the root mean square (RMS) of an AC voltage, but RMS is only about 71% of the peak voltage. Therefore, if the HVDC line can operate continuously with an HVDC voltage that is the same as the peak voltage of the AC equivalent line, then for a given current (where HVDC current is the same as the RMS current in the AC line), the power transmission capability when operating with HVDC is approximately 40% higher than the capability when operating with AC.
Asynchronous connections
Because HVDC allows power transmission between unsynchronized AC distribution systems, it can help increase system stability, by preventing cascading failures from propagating from one part of a wider power transmission grid to another. Changes in load that would cause portions of an AC network to become unsynchronized and to separate, would not similarly affect a DC link, and the power flow through the DC link would tend to stabilize the AC network. The magnitude and direction of power flow through a DC link can be directly controlled and changed as needed to support the AC networks at either end of the DC link.
Disadvantages
The disadvantages of HVDC are in conversion, switching, control, availability, and maintenance.
HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to the extra conversion equipment. Single-pole systems have availability of about 98.5%, with about a third of the downtime unscheduled due to faults. Fault-tolerant bipole systems provide high availability for 50% of the link capacity, but availability of the full capacity is about 97% to 98%.
The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance. The cost of the converters may not be offset by reductions in line construction cost and power line loss.
Operating an HVDC scheme requires many spare parts to be kept, often exclusively for one system, as HVDC systems are less standardized than AC systems and technology changes more quickly. | High-voltage direct current | Wikipedia | 505 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
In contrast to AC systems, realizing multi-terminal systems is complex (especially with line commutated converters), as is expanding existing schemes to multi-terminal systems. Controlling power flow in a multi-terminal DC system requires good communication between all the terminals; power flow must be actively regulated by the converter control system instead of relying on the inherent impedance and phase angle properties of an AC transmission line. Multi-terminal systems are therefore rare. only two are in service: the Quebec – New England Transmission between Radisson, Sandy Pond, and Nicolet and the Sardinia–mainland Italy link which was modified in 1989 to also provide power to the island of Corsica.
High-voltage DC circuit breaker
HVDC circuit breakers are difficult to build because of arcing: under AC, the voltage inverts and in doing so crosses zero volts dozens of times a second. An AC arc will self-extinguish at one of these zero-crossing points because there cannot be an arc where there is no potential difference. DC will never cross zero volts and never self-extinguish, so arc distance and duration is far greater with DC than the same voltage AC. This means some mechanism must be included in the circuit breaker to force current to zero and extinguish the arc, otherwise arcing and contact wear would be too great to allow reliable switching.
In November 2012, ABB announced the first ultrafast HVDC circuit breaker. Mechanical circuit breakers are too slow for use in HVDC grids, although they have been used for years in other applications. Conversely, semiconductor breakers are fast enough but have a high resistance when conducting, wasting energy and generating heat in normal operation. The ABB breaker combines semiconductor and mechanical breakers to produce a hybrid breaker with both a fast break time and a low resistance in normal operation.
Costs
Generally, vendors of HVDC systems, such as GE Vernova, Siemens and ABB, do not specify pricing details of particular projects; such costs are typically proprietary information between the supplier and the client. Costs vary widely depending on the specifics of the project (such as power rating, circuit length, overhead vs. cabled route, land costs, site seismology, and AC network improvements required at either terminal). A detailed analysis of DC vs. AC transmission costs may be required in situations where there is no obvious technical advantage to DC, and economical reasoning alone drives the selection.
However, some practitioners have provided some information: | High-voltage direct current | Wikipedia | 506 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
An April 2010 announcement for a 2,000 MW, line between Spain and France is estimated at €700 million. This includes the cost of a tunnel through the Pyrenees.
Conversion process
Converter
At the heart of an HVDC converter station, the equipment that performs the conversion between AC and DC is referred to as the converter. Almost all HVDC converters are inherently capable of converting from AC to DC (rectification) and from DC to AC (inversion), although in many HVDC systems, the system as a whole is optimized for power flow in only one direction. Irrespective of how the converter itself is designed, the station that is operating (at a given time) with power flow from AC to DC is referred to as the rectifier and the station that is operating with power flow from DC to AC is referred to as the inverter.
Early HVDC systems used electromechanical conversion (the Thury system) but all HVDC systems built since the 1940s have used electronic converters. Electronic converters for HVDC are divided into two main categories:
Line-commutated converters
Voltage-sourced converters
Line-commutated converters
Most of the HVDC systems in operation today are based on line-commutated converters (LCCs).
The basic LCC configuration uses a three-phase bridge rectifier known as a six-pulse bridge, containing six electronic switches, each connecting one of the three phases to one of the two DC rails. A complete switching element is usually referred to as a valve, irrespective of its construction. However, with a phase change only every 60°, considerable harmonic distortion is produced at both the DC and AC terminals when this arrangement is used.
An enhancement of this arrangement uses 12 valves in a twelve-pulse bridge. The AC is split into two separate three-phase supplies before transformation. One of the sets of supplies is then configured to have a star (wye) secondary, and the other a delta secondary, establishing a 30° phase difference between the two sets of three phases. With twelve valves connecting each of the two sets of three phases to the two DC rails, there is a phase change every 30°, and harmonics are considerably reduced. For this reason, the twelve-pulse system has become standard on most line-commutated converter HVDC systems built since the 1970s. | High-voltage direct current | Wikipedia | 502 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
With line commutated converters, the converter has only one degree of freedom the firing angle, which represents the time delay between the voltage across a valve becoming positive (at which point the valve would start to conduct if it were made from diodes) and the thyristors being turned on. The DC output voltage of the converter steadily becomes less positive as the firing angle is increased: firing angles of up to 90° correspond to rectification and result in positive DC voltages, while firing angles above 90° correspond to inversion and result in negative DC voltages. The practical upper limit for the firing angle is about 150–160° because above this, the valve would have insufficient turnoff time.
Early LCC systems used mercury-arc valves, which were rugged but required high maintenance. Because of this, many mercury-arc HVDC systems were built with bypass switchgear across each six-pulse bridge so that the HVDC scheme could be operated in six-pulse mode for short maintenance periods. The last mercury arc system was shut down in 2012.
The thyristor valve was first used in HVDC systems in 1972. The thyristor is a solid-state semiconductor device similar to the diode, but with an extra control terminal that is used to switch the device on at a particular instant during the AC cycle. Because the voltages in HVDC systems, up to 800 kV in some cases, far exceed the breakdown voltages of the thyristors used, HVDC thyristor valves are built using large numbers of thyristors in series. Additional passive components such as grading capacitors and resistors need to be connected in parallel with each thyristor in order to ensure that the voltage across the valve is evenly shared between the thyristors. The thyristor plus its grading circuits and other auxiliary equipment is known as a thyristor level. | High-voltage direct current | Wikipedia | 387 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Each thyristor valve will typically contain tens or hundreds of thyristor levels, each operating at a different (high) potential with respect to earth. The command information to turn on the thyristors therefore cannot simply be sent using a wire connection it needs to be isolated. The isolation method can be magnetic but is usually optical. Two optical methods are used: indirect and direct optical triggering. In the indirect optical triggering method, low-voltage control electronics send light pulses along optical fibers to the high-side control electronics, which derives its power from the voltage across each thyristor. The alternative direct optical triggering method dispenses with most of the high-side electronics, instead using light pulses from the control electronics to switch light-triggered thyristors (LTTs).
In a line-commutated converter, the DC current (usually) cannot change direction; it flows through a large inductance and can be considered almost constant. On the AC side, the converter behaves approximately as a current source, injecting both grid-frequency and harmonic currents into the AC network. For this reason, a line commutated converter for HVDC is also considered as a current-source inverter.
Voltage-sourced converters
Because thyristors can only be turned on (not off) by control action, the control system has only one degree of freedom – when to turn on the thyristor. This is an important limitation in some circumstances. | High-voltage direct current | Wikipedia | 301 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
With some other types of semiconductor devices such as the insulated-gate bipolar transistor (IGBT), both turn-on and turn-off can be controlled, giving a second degree of freedom. As a result, they can be used to make self-commutated converters. In such converters, the electric polarity of DC voltage is usually fixed and the DC voltage, being smoothed by a large capacitance, can be considered constant. For this reason, an HVDC converter using IGBTs is usually referred to as a voltage-sourced converter. The additional controllability gives many advantages, notably the ability to switch the IGBTs on and off many times per cycle in order to improve the harmonic performance. Being self-commutated, the converter no longer relies on synchronous machines in the AC system for its operation. A voltage-sourced converter can therefore feed power to an AC network consisting only of passive loads, something which is impossible with LCC HVDC.
HVDC systems based on voltage-sourced converters normally use the six-pulse connection because the converter produces much less harmonic distortion than a comparable LCC and the twelve-pulse connection is unnecessary.
Most of the VSC HVDC systems built until 2012 were based on the two-level converter, which can be thought of as a six-pulse bridge in which the thyristors have been replaced by IGBTs with inverse-parallel diodes and the DC smoothing reactors have been replaced by DC smoothing capacitors. Such converters derive their name from the discrete, two voltage levels at the AC output of each phase that correspond to the electrical potentials of the positive and negative DC terminals. Pulse-width modulation (PWM) is usually used to improve the harmonic distortion of the converter.
Some HVDC systems have been built with three-level converters, but today most new VSC HVDC systems are being built with some form of multilevel converter, most commonly the modular multilevel converter (MMC), in which each valve consists of a number of independent converter submodules, each containing its own storage capacitor. The IGBTs in each submodule either bypass the capacitor or connect it into the circuit, allowing the valve to synthesize a stepped voltage with very low levels of harmonic distortion.
Converter transformers | High-voltage direct current | Wikipedia | 500 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
At the AC side of each converter, a bank of transformers, often three physically separated single-phase transformers, isolate the station from the AC supply, to provide a local earth, and to ensure the correct eventual DC voltage. The output of these transformers is then connected to the converter.
Converter transformers for LCC HVDC schemes are quite specialized because of the high levels of harmonic currents that flow through them, and because the secondary winding insulation experiences a permanent DC voltage, which affects the design of the insulating structure inside the tank. In LCC systems, the transformers also need to provide the 30° phase shift required for harmonic cancellation.
Converter transformers for VSC HVDC systems are usually simpler and more conventional in design than those for LCC HVDC systems.
Reactive power
A major drawback of HVDC systems using line-commutated converters is that the converters inherently consume reactive power. The AC current flowing into the converter from the AC system lags behind the AC voltage so that, irrespective of the direction of active power flow, the converter always absorbs reactive power, behaving in the same way as a shunt reactor. The reactive power absorbed is at least under ideal conditions and can be higher than this when the converter is operating at higher than usual firing or extinction angle, or reduced DC voltage.
Although at HVDC converter stations connected directly to power stations some of the reactive power may be provided by the generators themselves, in most cases the reactive power consumed by the converter must be provided by banks of shunt capacitors connected at the AC terminals of the converter. The shunt capacitors are usually connected directly to the grid voltage but in some cases may be connected to a lower voltage via a tertiary winding on the converter transformer.
Since the reactive power consumed depends on the active power being transmitted, the shunt capacitors usually need to be subdivided into a number of switchable banks (typically four per converter) in order to prevent a surplus of reactive power being generated at low transmitted power.
The shunt capacitors are almost always provided with tuning reactors and, where necessary, damping resistors so that they can perform a dual role as harmonic filters.
VSCs, on the other hand, can either produce or consume reactive power on demand, with the result that usually no separate shunt capacitors are needed (other than those required purely for filtering).
Harmonics and filtering | High-voltage direct current | Wikipedia | 507 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
All power electronic converters generate some degree of harmonic distortion on the AC and DC systems to which they are connected, and HVDC converters are no exception.
With the recently developed modular multilevel converter (MMC), levels of harmonic distortion may be practically negligible, but with line-commutated converters and simpler types of VSCs, considerable harmonic distortion may be produced on both the AC and DC sides of the converter. As a result, harmonic filters are nearly always required at the AC terminals of such converters, and in HVDC transmission schemes using overhead lines, may also be required on the DC side.
Filters for line-commutated converters
The basic building-block of a line-commutated HVDC converter is the six-pulse bridge. This arrangement produces very high levels of harmonic distortion by acting as a current source injecting harmonic currents of order 6n±1 into the AC system and generating harmonic voltages of order 6n superimposed on the DC voltage.
It is very costly to provide harmonic filters capable of suppressing such harmonics, so a variant known as the twelve-pulse bridge (consisting of two six-pulse bridges in series with a 30° phase shift between them) is nearly always used. With the twelve-pulse arrangement, harmonics are still produced but only at orders 12n±1 on the AC side and 12n on the DC side. The task of suppressing such harmonics is still challenging, but manageable.
Line-commutated converters for HVDC are usually provided with combinations of harmonic filters designed to deal with the 11th and 13th harmonics on the AC side, and 12th harmonic on the DC side. Sometimes, high-pass filters may be provided to deal with 23rd, 25th, 35th, 37th... on the AC side and 24th, 36th... on the DC side. Sometimes, the AC filters may also need to provide damping at lower-order, noncharacteristic harmonics such as 3rd or 5th harmonics. | High-voltage direct current | Wikipedia | 422 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
The task of designing AC harmonic filters for HVDC converter stations is complex and computationally intensive, since in addition to ensuring that the converter does not produce an unacceptable level of voltage distortion on the AC system, it must be ensured that the harmonic filters do not resonate with some component elsewhere in the AC system. A detailed knowledge of the harmonic impedance of the AC system, at a wide range of frequencies, is needed in order to design the AC filters.
DC filters are required only for HVDC transmission systems involving overhead lines. Voltage distortion is not a problem in its own right, since consumers do not connect directly to the DC terminals of the system, so the main design criterion for the DC filters is to ensure that the harmonic currents flowing in the DC lines do not induce interference in nearby open-wire telephone lines. With the rise in digital mobile telecommunications systems, which are much less susceptible to interference, DC filters are becoming less important for HVDC systems.
Filters for voltage-sourced converters
Some types of voltage-sourced converters may produce such low levels of harmonic distortion that no filters are required at all. However, converter types such as the two-level converter, used with pulse-width modulation (PWM), still require some filtering, albeit less than on line-commutated converter systems.
With such converters, the harmonic spectrum is generally shifted to higher frequencies than with line-commutated converters. This usually allows the filter equipment to be smaller. The dominant harmonic frequencies are sidebands of the PWM frequency and multiples thereof. In HVDC applications, the PWM frequency is typically around 1 to 2 kHz.
Configurations
Monopole
In a monopole configuration one of the terminals of the rectifier is connected to earth ground. The other terminal, at high voltage relative to ground, is connected to a transmission line. The earthed terminal may be connected to the corresponding connection at the inverting station by means of a second conductor.
If no metallic return conductor is installed, current flows in the earth (or water) between two electrodes. This arrangement is a type of single-wire earth return system. | High-voltage direct current | Wikipedia | 445 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
The electrodes are usually located some tens of kilometers from the stations and are connected to the stations via a medium-voltage electrode line. The design of the electrodes themselves depends on whether they are located on land, on the shore or at sea. For the monopolar configuration with earth return, the earth current flow is unidirectional, which means that the design of one of the electrodes (the cathode) can be relatively simple, although the design of anode electrode is quite complex.
For long-distance transmission, earth return can be considerably cheaper than alternatives using a dedicated neutral conductor, but it can lead to problems such as:
Electrochemical corrosion of long buried metal objects such as pipelines
Underwater earth-return electrodes in seawater may produce chlorine or otherwise affect water chemistry
An unbalanced current path may result in a net magnetic field, which can affect magnetic navigational compasses for ships passing over an underwater cable.
These effects can be eliminated with installation of a metallic return conductor between the two ends of the monopolar transmission line. Since one terminal of the converters is connected to earth, the return conductor need not be insulated for the full transmission voltage which makes it less costly than the high-voltage conductor. The decision of whether or not to use a metallic return conductor is based upon economic, technical and environmental factors.
Modern monopolar systems for pure overhead lines carry typically 1.5 GW. If underground or underwater cables are used, the typical value is 600 MW.
Most monopolar systems are designed for future bipolar expansion. Transmission line towers may be designed to carry two conductors, even if only one is used initially for the monopole transmission system. The second conductor is either unused, used as electrode line or connected in parallel with the other (as in case of Baltic Cable).
Symmetrical monopole
An alternative is to use two high-voltage conductors, operating at about half of the DC voltage, with only a single converter at each end. In this arrangement, known as the symmetrical monopole, the converters are earthed only via a high impedance and there is no earth current. The symmetrical monopole arrangement is uncommon with line-commutated converters (the NorNed interconnector being a rare example) but is very common with Voltage Sourced Converters when cables are used.
Bipolar | High-voltage direct current | Wikipedia | 479 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
In bipolar transmission a pair of conductors is used, each at a high potential with respect to ground, in opposite polarity. Since these conductors must be insulated for the full voltage, transmission line cost is higher than a monopole with a return conductor. However, there are a number of advantages to bipolar transmission which can make it an attractive option.
Under normal load, negligible earth-current flows, as in the case of monopolar transmission with a metallic earth-return. This reduces earth return loss and environmental effects.
When a fault develops in a line, with earth return electrodes installed at each end of the line, approximately half the rated power can continue to flow using the earth as a return path, operating in monopolar mode.
Since for a given total power rating each conductor of a bipolar line carries only half the current of monopolar lines, the cost of the second conductor is reduced compared to a monopolar line of the same rating.
In very adverse terrain, the second conductor may be carried on an independent set of transmission towers, so that some power may continue to be transmitted even if one line is damaged.
A bipolar system may also be installed with a metallic earth return conductor.
Bipolar systems may carry as much as 4 GW at voltages of ±660 kV with a single converter per pole, as on the Ningdong–Shandong project in China. With a power rating of 2,000 MW per twelve-pulse converter, the converters for that project were (as of 2010) the most powerful HVDC converters ever built. Even higher powers can be achieved by connecting two or more twelve-pulse converters in series in each pole, as is used in the ±800 kV Xiangjiaba–Shanghai project in China, which uses two twelve-pulse converter bridges in each pole, each rated at 400 kV DC and 1,600 MW.
Submarine cable installations initially commissioned as a monopole may be upgraded with additional cables and operated as a bipole.
A bipolar scheme can be implemented so that the polarity of one or both poles can be changed. This allows the operation as two parallel monopoles. If one conductor fails, transmission can still continue at reduced capacity. Losses may increase if ground electrodes and lines are not designed for the extra current in this mode. To reduce losses in this case, intermediate switching stations may be installed, at which line segments can be switched off or parallelized. This was done at Inga–Shaba HVDC. | High-voltage direct current | Wikipedia | 512 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Back to back
A back-to-back station (or B2B for short) is a plant in which both converters are in the same area, usually in the same building. The length of the direct current line is kept as short as possible. HVDC back-to-back stations are used for
coupling of electricity grids of different frequencies (as in Japan and South America; and the GCC interconnector between Saudi Arabia (60 Hz) and rest of GCC countries (50 Hz) completed in 2009)
coupling two networks of the same nominal frequency but no fixed phase relationship (as until 1995/96 in Etzenricht, Dürnrohr, Vienna, and the Vyborg HVDC scheme).
different frequency and phase number (for example, as a replacement for traction current converter plants)
The DC voltage in the intermediate circuit can be selected freely at HVDC back-to-back stations because of the short conductor length. The DC voltage is usually selected to be as low as possible, in order to build a small valve hall and to reduce the number of thyristors connected in series in each valve. For this reason, at HVDC back-to-back stations, valves with the highest available current rating (in some cases, up to 4,500 A) are used.
Multi-terminal systems
The most common configuration of an HVDC link consists of two converter stations connected by an overhead power line or undersea cable.
Multi-terminal HVDC links, connecting more than two points, are rare. The configuration of multiple terminals can be series, parallel, or hybrid (a mixture of series and parallel). Parallel configuration tends to be used for large capacity stations, and series for lower capacity stations. An example is the 2,000 MW Quebec - New England Transmission system opened in 1992, which is currently the largest multi-terminal HVDC system in the world.
Multi-terminal systems are difficult to realize using line commutated converters because reversals of power are effected by reversing the polarity of DC voltage, which affects all converters connected to the system. With Voltage Sourced Converters, power reversal is achieved instead by reversing the direction of current, making parallel-connected multi-terminals systems much easier to control. For this reason, multi-terminal systems are expected to become much more common in the near future. | High-voltage direct current | Wikipedia | 492 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
China is expanding its grid to keep up with increased power demand, while addressing environmental targets. China Southern Power Grid started a three terminals VSC HVDC pilot project in 2011. The project has designed ratings of ±160 kV/200 MW-100 MW-50 MW and will be used to bring wind power generated on Nanao island into the mainland Guangdong power grid through of combination of HVDC land cables, sea cables and overhead lines. This project was put into operation on December 19, 2013.
In India, the multi-terminal North-East Agra project is planned for commissioning in 2015–2017. It is rated 6,000 MW, and it transmits power on a ±800 kV bipolar line from two converter stations, at Biswanath Chariali and Alipurduar, in the east to a converter at Agra, a distance of .
Other arrangements
Cross-Skagerrak consisted since 1993 of 3 poles, from which 2 were switched in parallel and the third used an opposite polarity with a higher transmission voltage. This configuration ended in 2014 when poles 1 and 2 again were rebuilt to work in bipole and pole 3 (LCC) works in bipole with a new pole 4 (VSC). This is the first HVDC transmission where LCC and VSC poles cooperate in a bipole.
A similar arrangement was the HVDC Inter-Island in New Zealand after a capacity upgrade in 1992, in which the two original converters (using mercury-arc valves) were parallel-switched feeding the same pole and a new third (thyristor) converter installed with opposite polarity and higher operation voltage. This configuration ended in 2012 when the two old converters were replaced with a single, new, thyristor converter.
A scheme patented in 2004 is intended for conversion of existing AC transmission lines to HVDC. Two of the three circuit conductors are operated as a bipole. The third conductor is used as a parallel monopole, equipped with reversing valves (or parallel valves connected in reverse polarity). This allows heavier currents to be carried by the bipole conductors, and full use of the installed third conductor for energy transmission. High currents can be circulated through the line conductors even when load demand is low, for removal of ice. , no tripole conversions are in operation, although a transmission line in India has been converted to bipole HVDC (HVDC Sileru-Barsoor). | High-voltage direct current | Wikipedia | 503 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
Corona discharge
Corona discharge is the creation of ions in a fluid (such as air) by the presence of a strong electric field. Electrons are torn from neutral air, and either the positive ions or the electrons are attracted to the conductor, while the charged particles drift. This effect can cause considerable power loss, create audible and radio-frequency interference, generate toxic compounds such as oxides of nitrogen and ozone, and bring forth arcing.
Both AC and DC transmission lines can generate coronas, in the former case in the form of oscillating particles, in the latter a constant wind. Due to the space charge formed around the conductors, an HVDC system may have about half the loss per unit length of a high voltage AC system carrying the same amount of power. With monopolar transmission the choice of polarity of the energized conductor leads to a degree of control over the corona discharge. In particular, the polarity of the ions emitted can be controlled, which may have an environmental impact on ozone creation. Negative coronas generate considerably more ozone than positive coronas, and generate it further downwind of the power line, creating the potential for health effects. The use of a positive voltage will reduce the ozone impacts of monopole HVDC power lines.
Applications
Overview
The controllability of a current-flow through HVDC rectifiers and inverters, their application in connecting unsynchronized networks, and their applications in efficient submarine cables mean that HVDC interconnectors are often used at national or regional boundaries for the exchange of power (in North America, HVDC connections divide much of Canada and the United States into several electrical regions that cross national borders, although the purpose of these connections is still to connect unsynchronized AC grids to each other). Offshore windfarms also require undersea cables, and their turbines are unsynchronized. In very long-distance connections between two locations, such as power transmission from a large hydroelectric power plant at a remote site to an urban area, HVDC transmission systems may appropriately be used; several schemes of these kind have been built. For interconnectors to Siberia, Canada, India, and the Scandinavian North, the decreased line-costs of HVDC also make it applicable, see List of HVDC projects. Other applications are noted throughout this article. | High-voltage direct current | Wikipedia | 486 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
AC network interconnectors
AC transmission lines can interconnect only synchronized AC networks with the same frequency with limits on the allowable phase difference between the two ends of the line. Many areas that wish to share power have unsynchronized networks. The power grids of the UK, Northern Europe and continental Europe are not united into a single synchronized network. Japan has 50 Hz and 60 Hz networks. Continental North America, while operating at 60 Hz throughout, is divided into regions which are unsynchronized: East, West, Texas, Quebec, and Alaska. Brazil and Paraguay, which share the enormous Itaipu Dam hydroelectric plant, operate on 60 Hz and 50 Hz respectively. However, HVDC systems make it possible to interconnect unsynchronized AC networks, and also add the possibility of controlling AC voltage and reactive power flow.
A generator connected to a long AC transmission line may become unstable and fall out of synchronization with a distant AC power system. An HVDC transmission link may make it economically feasible to use remote generation sites. Wind farms located off-shore may use HVDC systems to collect power from multiple unsynchronized generators for transmission to the shore by an underwater cable.
In general, however, an HVDC power line will interconnect two AC regions of the power-distribution grid. Machinery to convert between AC and DC power adds a considerable cost in power transmission. The conversion from AC to DC is known as rectification, and from DC to AC as inversion. Above a certain break-even distance (about for submarine cables, and perhaps for overhead cables), the lower cost of the HVDC electrical conductors outweighs the cost of the electronics.
The conversion electronics also present an opportunity to effectively manage the power grid by means of controlling the magnitude and direction of power flow. An additional advantage of the existence of HVDC links, therefore, is potential increased stability in the transmission grid.
Renewable electricity superhighways | High-voltage direct current | Wikipedia | 411 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
A number of studies have highlighted the potential benefits of very wide area super grids based on HVDC since they can mitigate the effects of intermittency by averaging and smoothing the outputs of large numbers of geographically dispersed wind farms or solar farms. Czisch's study concludes that a grid covering the fringes of Europe could bring 100% renewable power (70% wind, 30% biomass) at close to today's prices. There has been debate over the technical feasibility of this proposal and the political risks involved in energy transmission across a large number of international borders.
The construction of such green power superhighways is advocated in a white paper that was released by the American Wind Energy Association and the Solar Energy Industries Association in 2009. Clean Line Energy Partners is developing four HVDC lines in the U.S. for long-distance electric power transmission.
In January 2009, the European Commission proposed €300 million to subsidize the development of HVDC links between Ireland, Britain, the Netherlands, Germany, Denmark, and Sweden, as part of a wider €1.2 billion package supporting links to offshore wind farms and cross-border interconnectors throughout Europe. Meanwhile, the recently founded Union of the Mediterranean has embraced a Mediterranean Solar Plan to import large amounts of concentrated solar power into Europe from North Africa and the Middle East. Japan-Taiwan-Philippines HVDC interconnector was proposed in 2020. The purpose of this interconnector is to facilitate cross-border renewable power trading with Indonesia and Australia, in preparation for the future Asian Pacific Super Grid.
Advancements in UHVDC
UHVDC (ultrahigh-voltage direct-current) is shaping up to be the latest technological front in high voltage DC transmission technology. UHVDC is defined as DC voltage transmission of above 800 kV (HVDC is generally just 100 to 800 kV).
One of the problems with current UHVDC supergrids is that – although less than AC transmission or DC transmission at lower voltages – they still suffer from power loss as the length is extended. A typical loss for 800 kV lines is 2.6% over . Increasing the transmission voltage on such lines reduces the power loss, but until recently, the interconnectors required to bridge the segments were prohibitively expensive. However, with advances in manufacturing, it is becoming more and more feasible to build UHVDC lines. | High-voltage direct current | Wikipedia | 492 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
In 2010, ABB Group built the world's first 800 kV UHVDC in China. The Zhundong–Wannan UHVDC line with 1100 kV, length and 12 GW capacity was completed in 2018. As of 2020, at least thirteen UHVDC transmission lines in China have been completed.
While the majority of recent UHVDC technology deployment is in China, it has also been deployed in South America as well as other parts of Asia. In India, a , 800 kV, 6 GW line between Raigarh and Pugalur is expected to be completed in 2019. In Brazil, the Xingu-Estreito line over with 800 kV and 4 GW was completed in 2017, and the Xingu-Rio line over with 800 kV and 4 GW was completed in 2019, both to transmit the energy from Belo Monte Dam. As of 2020, no UHVDC line (≥ 800 kV) exists in Europe or North America.
A 1,100 kV link in China was completed in 2019 over a distance of with a power capacity of 12 GW. With this dimension, intercontinental connections become possible which could help to deal with the fluctuations of wind power and photovoltaics. | High-voltage direct current | Wikipedia | 249 | 47716 | https://en.wikipedia.org/wiki/High-voltage%20direct%20current | Technology | Electricity transmission and distribution | null |
The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI). It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second. It is used to define the elementary charge e.
Definition
The SI defines the coulomb as "the quantity of electricity carried in 1 second by a current of 1 ampere". Then the value of the elementary charge e is defined to be . Since the coulomb is the reciprocal of the elementary charge,
it is approximately and is thus not an integer multiple of the elementary charge.
The coulomb was previously defined in terms of the force between two wires. The coulomb was originally defined, using the latter definition of the ampere, as .
The 2019 redefinition of the ampere and other SI base units fixed the numerical value of the elementary charge when expressed in coulombs and therefore fixed the value of the coulomb when expressed as a multiple of the fundamental charge.
SI prefixes
Like other SI units, the coulomb can be modified by adding a prefix that multiplies it by a power of 10.
Conversions
The magnitude of the electrical charge of one mole of elementary charges (approximately , the Avogadro number) is known as a faraday unit of charge (closely related to the Faraday constant). One faraday equals In terms of the Avogadro constant (NA), one coulomb is equal to approximately × NA elementary charges.
Every farad of capacitance can hold one coulomb per volt across the capacitor.
One ampere hour equals , hence = .
One statcoulomb (statC), the obsolete CGS electrostatic unit of charge (esu), is approximately or about one-third of a nanocoulomb.
In everyday terms
The charges in static electricity from rubbing materials together are typically a few microcoulombs.
The amount of charge that travels through a lightning bolt is typically around 15 C, although for large bolts this can be up to 350 C.
The amount of charge that travels through a typical alkaline AA battery from being fully charged to discharged is about = ≈ .
A typical smartphone battery can hold ≈ .
Name and history | Coulomb | Wikipedia | 463 | 47719 | https://en.wikipedia.org/wiki/Coulomb | Physical sciences | Electromagnetism | null |
By 1878, the British Association for the Advancement of Science had defined the volt, ohm, and farad, but not the coulomb. In 1881, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force, the ampere as the unit for electric current, and the coulomb as the unit of electric charge.
At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one ampere dissipates one watt of power.
The coulomb (later "absolute coulomb" or "abcoulomb" for disambiguation) was part of the EMU system of units. The "international coulomb" based on laboratory specifications for its measurement was introduced by the IEC in 1908. The entire set of "reproducible units" was abandoned in 1948 and the "international coulomb" became the modern coulomb. | Coulomb | Wikipedia | 222 | 47719 | https://en.wikipedia.org/wiki/Coulomb | Physical sciences | Electromagnetism | null |
The Brooklyn Bridge is a hybrid cable-stayed/suspension bridge in New York City, spanning the East River between the boroughs of Manhattan and Brooklyn. Opened on May 24, 1883, the Brooklyn Bridge was the first fixed crossing of the East River. It was also the longest suspension bridge in the world at the time of its opening, with a main span of and a deck above Mean High Water. The span was originally called the New York and Brooklyn Bridge or the East River Bridge but was officially renamed the Brooklyn Bridge in 1915.
Proposals for a bridge connecting Manhattan and Brooklyn were first made in the early 19th century, which eventually led to the construction of the current span, designed by John A. Roebling. The project's chief engineer, his son Washington Roebling, contributed further design work, assisted by the latter's wife, Emily Warren Roebling. Construction started in 1870 and was overseen by the New York Bridge Company, which in turn was controlled by the Tammany Hall political machine. Numerous controversies and the novelty of the design prolonged the project over thirteen years. After opening, the Brooklyn Bridge underwent several reconfigurations, having carried horse-drawn vehicles and elevated railway lines until 1950. To alleviate increasing traffic flows, additional bridges and tunnels were built across the East River. Following gradual deterioration, the Brooklyn Bridge was renovated several times, including in the 1950s, 1980s, and 2010s.
The Brooklyn Bridge is the southernmost of four vehicular bridges directly connecting Manhattan Island and Long Island, with the Manhattan Bridge, the Williamsburg Bridge, and the Queensboro Bridge to the north. Only passenger vehicles and pedestrian and bicycle traffic are permitted. A major tourist attraction since its opening, the Brooklyn Bridge has become an icon of New York City. Over the years, the bridge has been used as the location of various stunts and performances, as well as several crimes, attacks and vandalism. The Brooklyn Bridge is designated a National Historic Landmark, a New York City landmark, and a National Historic Civil Engineering Landmark.
Description
The Brooklyn Bridge, an early example of a steel-wire suspension bridge, uses a hybrid cable-stayed/suspension bridge design, with both vertical and diagonal suspender cables. Its stone towers are neo-Gothic, with characteristic pointed arches. The New York City Department of Transportation (NYCDOT), which maintains the bridge, says that its original paint scheme was "Brooklyn Bridge Tan" and "Silver", but other accounts state that it was originally entirely "Rawlins Red".
Deck | Brooklyn Bridge | Wikipedia | 503 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
To provide sufficient clearance for shipping in the East River, the Brooklyn Bridge incorporates long approach viaducts on either end to raise it from low ground on both shores. Including approaches, the Brooklyn Bridge is a total of long when measured between the curbs at Park Row in Manhattan and Sands Street in Brooklyn. A separate measurement of is sometimes given; this is the distance from the curb at Centre Street in Manhattan.
Suspension span
The main span between the two suspension towers is long and wide. The bridge "elongates and contracts between the extremes of temperature from 14 to 16 inches". Navigational clearance is above Mean High Water (MHW). A 1909 Engineering Magazine article said that, at the center of the span, the height above MHW could fluctuate by more than due to temperature and traffic loads, while more rigid spans had a lower maximum deflection.
The side spans, between each suspension tower and each side's suspension anchorages, are long. At the time of construction, engineers had not yet discovered the aerodynamics of bridge construction, and bridge designs were not tested in wind tunnels. John Roebling designed the Brooklyn Bridge's truss system to be six to eight times as strong as he thought it needed to be. As such, the open truss structure supporting the deck is, by its nature, subject to fewer aerodynamic problems. However, due to a supplier's fraudulent substitution of inferior-quality wire in the initial construction, the bridge was reappraised at the time as being only four times as strong as necessary.
The main span and side spans are supported by a structure containing trusses that run parallel to the roadway, each of which is deep. Originally there were six trusses, but two were removed during a late-1940s renovation. The trusses allow the Brooklyn Bridge to hold a total load of , a design consideration from when it originally carried heavier elevated trains. These trusses are held up by suspender ropes, which hang downward from each of the four main cables. Crossbeams run between the trusses at the top, and diagonal and vertical stiffening beams run on the outside and inside of each roadway. | Brooklyn Bridge | Wikipedia | 436 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
An elevated pedestrian-only promenade runs in between the two roadways and above them. It typically runs below the level of the crossbeams, except at the areas surrounding each tower. Here, the promenade rises to just above the level of the crossbeams, connecting to a balcony that slightly overhangs the two roadways. The path is generally wide. The iron railings were produced by Janes & Kirtland, a Bronx iron foundry that also made the United States Capitol dome and the Bow Bridge in Central Park.
Approaches
Each of the side spans is reached by an approach ramp. The approach ramp from the Brooklyn side is shorter than the approach ramp from the Manhattan side. The approaches are supported by Renaissance-style arches made of masonry; the arch openings themselves were filled with brick walls, with small windows within. The approach ramp contains nine arch or iron-girder bridges across side streets in Manhattan and Brooklyn.
Underneath the Manhattan approach, a series of brick slopes or "banks" was developed into a skate park, the Brooklyn Banks, in the late 1980s. The park uses the approach's support pillars as obstacles. In the mid-2010s, the Brooklyn Banks were closed to the public because the area was being used as a storage site during the bridge's renovation. The skateboarding community has attempted to save the banks on multiple occasions; after the city destroyed the smaller banks in the 2000s, the city government agreed to keep the larger banks for skateboarding. When the NYCDOT removed the bricks from the banks in 2020, skateboarders started an online petition. In the 2020s, local resident Rosa Chang advocated for the space under the Manhattan approach to be converted into a recreational area known as Gotham Park. Some of the space under the Manhattan approach reopened in May 2023 as a park called the Arches; this was followed in November 2024 by another section of parkland.
Cables | Brooklyn Bridge | Wikipedia | 382 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The Brooklyn Bridge contains four main cables, which descend from the tops of the suspension towers and help support the deck. Two are located to the outside of the bridge's roadways, while two are in the median of the roadways. Each main cable measures in diameter and contains 5,282 parallel, galvanized steel wires wrapped closely together in a cylindrical shape. These wires are bundled in 19 individual strands, with 278 wires to a strand. This was the first use of bundling in a suspension bridge and took several months for workers to tie together. Since the 2000s, the main cables have also supported a series of 24-watt LED lighting fixtures, referred to as "necklace lights" due to their shape.
In addition, either 1,088, 1,096, or 1,520 galvanized steel wire suspender cables hang downward from the main cables. Another 400 cable stays extend diagonally from the towers. The vertical suspender cables and diagonal cable stays hold up the truss structure around the bridge deck. The bridge's suspenders originally used wire rope, which was replaced in the 1980s with galvanized steel made by Bethlehem Steel. The vertical suspender cables measure long, and the diagonal stays measure long.
Anchorages
Each side of the bridge contains an anchorage for the main cables. The anchorages are trapezoidal limestone structures located slightly inland of the shore, measuring at the base and at the top. Each anchorage weighs . The Manhattan anchorage rests on a foundation of bedrock while the Brooklyn anchorage rests on clay.
The anchorages both have four anchor plates, one for each of the main cables, which are located near ground level and parallel to the ground. The anchor plates measure , with a thickness of and weigh each. Each anchor plate is connected to the respective main cable by two sets of nine eyebars, each of which is about long and up to thick. The chains of eyebars curve downward from the cables toward the anchor plates, and the eyebars vary in size depending on their position. | Brooklyn Bridge | Wikipedia | 412 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The anchorages also contain numerous passageways and compartments. Starting in 1876, in order to fund the bridge's maintenance, the New York City government made the large vaults under the bridge's Manhattan anchorage available for rent, and they were in constant use during the early 20th century. The vaults were used to store wine, as they were kept at a consistent temperature due to a lack of air circulation. The Manhattan vault was called the "Blue Grotto" because of a shrine to the Virgin Mary next to an opening at the entrance. The vaults were closed for public use in the late 1910s and 1920s during World War I and Prohibition but were reopened thereafter. When New York magazine visited one of the cellars in 1978, it discovered a "fading inscription" on a wall reading: "Who loveth not wine, women and song, he remaineth a fool his whole life long." Leaks found within the vault's spaces necessitated repairs during the late 1980s and early 1990s. By the late 1990s, the chambers were being used to store maintenance equipment.
Towers
The bridge's two suspension towers are tall with a footprint of at the high water line. They are built of limestone, granite, and Rosendale cement. The limestone was quarried at the Clark Quarry in Essex County, New York. The granite blocks were quarried and shaped on Vinalhaven Island, Maine, under a contract with the Bodwell Granite Company, and delivered from Maine to New York by schooner. The Manhattan tower contains of masonry, while the Brooklyn tower has of masonry. There are 56 LED lamps mounted onto the towers.
Each tower contains a pair of Gothic Revival pointed arches, through which the roadways run. The arch openings are tall and wide. The tops of the towers are located above the floor of each arch opening, while the floors of the openings are above mean water level, giving the towers a total height of above mean high water. | Brooklyn Bridge | Wikipedia | 390 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Caissons
The towers rest on underwater caissons made of southern yellow pine and filled with cement. Inside both caissons were spaces for construction workers. The Manhattan side's caisson is slightly larger, measuring and located below high water, while the Brooklyn side's caisson measures and is located below high water. The caissons were designed to hold at least the weight of the towers which would exert a pressure of when fully built, but the caissons were over-engineered for safety. During an accident on the Brooklyn side, when air pressure was lost and the partially-built towers dropped full-force down, the caisson sustained an estimated pressure of with only minor damage. Most of the timber used in the bridge's construction, including in the caissons, came from mills at Gascoigne Bluff on St. Simons Island, Georgia.
The Brooklyn side's caisson, which was built first, originally had a height of and a ceiling composed of five layers of timber, each layer tall. Ten more layers of timber were later added atop the ceiling, and the entire caisson was wrapped in tin and wood for further protection against flooding. The thickness of the caisson's sides was at both the bottom and the top. The caisson had six chambers: two each for dredging, supply shafts, and airlocks.
The caisson on the Manhattan side was slightly different because it had to be installed at a greater depth. To protect against the increased air pressure at that depth, the Manhattan caisson had 22 layers of timber on its roof, seven more than its Brooklyn counterpart had. The Manhattan caisson also had fifty pipes for sand removal, a fireproof iron-boilerplate interior, and different airlocks and communication systems.
History
Planning | Brooklyn Bridge | Wikipedia | 364 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Proposals for a bridge between the then-separate cities of Brooklyn and New York had been suggested as early as 1800. At the time, the only travel between the two cities was by a number of ferry lines. Engineers presented various designs, such as chain or link bridges, though these were never built because of the difficulties of constructing a high enough fixed-span bridge across the extremely busy East River. There were also proposals for tunnels under the East River, but these were considered prohibitively expensive. German immigrant engineer John Augustus Roebling proposed building a suspension bridge over the East River in 1857. He had previously designed and constructed shorter suspension bridges, such as Roebling's Delaware Aqueduct in Lackawaxen, Pennsylvania, and the Niagara Suspension Bridge. In 1867, Roebling erected what became the John A. Roebling Suspension Bridge over the Ohio River between Cincinnati, Ohio, and Covington, Kentucky.
In February 1867, the New York State Senate passed a bill that allowed the construction of a suspension bridge from Brooklyn to Manhattan. Two months later, the New York and Brooklyn Bridge Company was incorporated with a board of directors (later converted to a board of trustees). There were twenty trustees in total: eight each appointed by the mayors of New York and Brooklyn, as well as the mayors of each city and the auditor and comptroller of Brooklyn. The company was tasked with constructing what was then known as the New York and Brooklyn Bridge. Alternatively, the span was just referred to as the "Brooklyn Bridge", a name originating in a January 25, 1867, letter to the editor sent to the Brooklyn Daily Eagle. The act of incorporation, which became law on April 16, 1867, authorized the cities of New York (now Manhattan) and Brooklyn to subscribe to $5 million in capital stock, which would fund the bridge's construction. | Brooklyn Bridge | Wikipedia | 370 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Roebling was subsequently named the chief engineer of the work and, by September 1867, had presented a master plan. According to the plan, the bridge would be longer and taller than any suspension bridge previously built. It would incorporate roadways and elevated rail tracks, whose tolls and fares would provide the means to pay for the bridge's construction. It would also include a raised promenade that served as a leisurely pathway. The proposal received much acclaim in both cities, and residents predicted that the New York and Brooklyn Bridge's opening would have as much of an impact as the Suez Canal, the first transatlantic telegraph cable or the first transcontinental railroad. By early 1869, however, some individuals started to criticize the project, saying either that the bridge was too expensive, or that the construction process was too difficult.
To allay concerns about the design of the New York and Brooklyn Bridge, Roebling set up a "Bridge Party" in March 1869, where he invited engineers and members of U.S. Congress to see his other spans. Following the bridge party in April, Roebling and several engineers conducted final surveys. During the process, it was determined that the main span would have to be raised from above MHW, requiring several changes to the overall design. In June 1869, while conducting these surveys, Roebling sustained a crush injury to his foot when a ferry pinned it against a piling. After amputation of his crushed toes, he developed a tetanus infection that left him incapacitated and resulted in his death the following month. Washington Roebling, John Roebling's 32-year-old son, was then hired to fill his father's role. Tammany Hall leader William M. Tweed also became involved in the bridge's construction because, as a major landowner in New York City, he had an interest in the project's completion. The New York and Brooklyn Bridge Company—later known simply as the New York Bridge Company—was actually overseen by Tammany Hall, and it approved Roebling's plans and designated him as chief engineer of the project.
Construction
Caissons | Brooklyn Bridge | Wikipedia | 432 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Construction of the Brooklyn Bridge began on January 2, 1870. The first work entailed the construction of two caissons, upon which the suspension towers would be built. The Brooklyn side's caisson was built at the Webb & Bell shipyard in Greenpoint, Brooklyn, and was launched into the river on March 19, 1870. Compressed air was pumped into the caisson, and workers entered the space to dig the sediment until it sank to the bedrock. As one sixteen-year-old from Ireland, Frank Harris, described the fearful experience:The six of us were working naked to the waist in the small iron chamber with the temperature of about 80 degrees Fahrenheit: In five minutes the sweat was pouring from us, and all the while we were standing in icy water that was only kept from rising by the terrific pressure. No wonder the headaches were blinding. Once the caisson had reached the desired depth, it was to be filled in with vertical brick piers and concrete. However, due to the unexpectedly high concentration of large boulders atop the riverbed, the Brooklyn caisson took several months to sink to the desired depth. Furthermore, in December 1870, its timber roof caught fire, delaying construction further. The "Great Blowout", as the fire was called, delayed construction for several months, since the holes in the caisson had to be repaired. On March 6, 1871, the repairs were finished, and the caisson had reached its final depth of ; it was filled with concrete five days later. Overall, about 264 individuals were estimated to have worked in the caisson every day, but because of high worker turnover, the final total was thought to be about 2,500 men in total. In spite of this, only a few workers were paralyzed. At its final depth, the caisson's air pressure was . | Brooklyn Bridge | Wikipedia | 373 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The Manhattan side's caisson was the next structure to be built. To ensure that it would not catch fire like its counterpart had, the Manhattan caisson was lined with fireproof plate iron. It was launched from Webb & Bell's shipyard on May 11, 1871, and maneuvered into place that September. Due to the extreme underwater air pressure inside the much deeper Manhattan caisson, many workers became sick with "the bends"—decompression sickness—during this work, despite the incorporation of airlocks (which were believed to help with decompression sickness at the time). This condition was unknown at the time and was first called "caisson disease" by the project physician, Andrew Smith. Between January 25 and May 31, 1872, Smith treated 110 cases of decompression sickness, while three workers died from the disease. When iron probes underneath the Manhattan caisson found the bedrock to be even deeper than expected, Washington Roebling halted construction due to the increased risk of decompression sickness. After the Manhattan caisson reached a depth of with an air pressure of , Washington deemed the sandy subsoil overlying the bedrock beneath to be sufficiently firm, and subsequently infilled the caisson with concrete in July 1872.
Washington Roebling himself suffered a paralyzing injury as a result of caisson disease shortly after ground was broken for the Brooklyn tower foundation. His debilitating condition left him unable to supervise the construction in person, so he designed the caissons and other equipment from his apartment, directing "the completion of the bridge through a telescope from his bedroom." His wife, Emily Warren Roebling, not only provided written communications between her husband and the engineers on site, but also understood mathematics, calculations of catenary curves, strengths of materials, bridge specifications, and the intricacies of cable construction. She spent the next 11 years helping supervise the bridge's construction, taking over much of the chief engineer's duties, including day-to-day supervision and project management.
Towers | Brooklyn Bridge | Wikipedia | 415 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
After the caissons were completed, piers were constructed on top of each of them upon which masonry towers would be built. The towers' construction was a complex process that took four years. Since the masonry blocks were heavy, the builders transported them to the base of the towers using a pulley system with a continuous -diameter steel wire rope, operated by steam engines at ground level. The blocks were then carried up on a timber track alongside each tower and maneuvered into the proper position using a derrick atop the towers. The blocks sometimes vibrated the ropes because of their weight, but only once did a block fall.
Construction on the suspension towers started in mid-1872, and by the time work was halted for the winter in late 1872, parts of each tower had already been built. By mid-1873, there was substantial progress on the towers' construction. The Brooklyn side's tower had reached a height of above mean high water (MHW), while the tower on the Manhattan side had reached above MHW. The arches of the Brooklyn tower were completed by August 1874. The tower was substantially finished by December 1874 with the erection of saddle plates for the main cables at the top of the tower. However, the ornamentation on the Brooklyn tower could not be completed until the Manhattan tower was finished. The last stone on the Brooklyn tower was raised in June 1875 and the Manhattan tower was completed in July 1876. The saddle plates atop both towers were also raised in July 1876. The work was dangerous: by 1876, three workers had died having fallen from the towers, while nine other workers were killed in other accidents.
In 1875, while the towers were being constructed, the project had depleted its original $5 million budget. Two bridge commissioners, one each from Brooklyn and Manhattan, petitioned New York state lawmakers to allot another $8 million for construction. Ultimately, the legislators passed a law authorizing the allotment with the condition that the cities would buy the stock of Brooklyn Bridge's private stockholders.
Work proceeded concurrently on the anchorages on each side. The Brooklyn anchorage broke ground in January 1873 and was subsequently substantially completed in August 1875. The Manhattan anchorage was built in less time, having started in May 1875, it was mostly completed in July 1876. The anchorages could not be fully completed until the main cables were spun, at which point another would be added to the height of each anchorage. | Brooklyn Bridge | Wikipedia | 488 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Cables
The first temporary wire was stretched between the towers on August 15, 1876, using chrome steel provided by the Chrome Steel Company of Brooklyn. The wire was then stretched back across the river, and the two ends were spliced to form a traveler, a lengthy loop of wire connecting the towers, which was driven by a steam hoisting engine at ground level. The wire was one of two that were used to create a temporary footbridge for workers while cable spinning was ongoing. The next step was to send an engineer across the completed traveler wire in a boatswain's chair slung from the wire, to ensure it was safe enough. The bridge's master mechanic, E.F. Farrington, was selected for this task, and an estimated crowd of 10,000 people on both shores watched him cross. A second traveler wire was then stretched across the span, a task that was completed by August 30. The temporary footbridge, located some above the elevation of the future deck, was completed in February 1877.
By December 1876, a steel contract for the permanent cables still had not been awarded. There was disagreement over whether the bridge's cables should use the as-yet-untested Bessemer steel or the well-proven crucible steel. Until a permanent contract was awarded, the builders ordered of wire in the interim, 10 tons each from three companies, including Washington Roebling's own steel mill in Brooklyn. In the end, it was decided to use number 8 Birmingham gauge (approximately 4 mm or 0.165 inches in diameter) crucible steel, and a request for bids was distributed, to which eight companies responded. In January 1877, a contract for crucible steel was awarded to J. Lloyd Haigh, who was associated with bridge trustee Abram Hewitt, whom Roebling distrusted. | Brooklyn Bridge | Wikipedia | 370 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The spinning of the wires required the manufacture of large coils of it which were galvanized but not oiled when they left the factory. The coils were delivered to a yard near the Brooklyn anchorage. There they were dipped in linseed oil, hoisted to the top of the anchorage, dried out and spliced into a single wire, and finally coated with red zinc for further galvanizing. There were thirty-two drums at the anchorage yard, eight for each of the four main cables. Each drum had a capacity of of wire. The first experimental wire for the main cables was stretched between the towers on May 29, 1877, and spinning began two weeks later. All four main cables were being strung by that July. During that time, the temporary footbridge was unofficially opened to members of the public, who could receive a visitor's pass; by August 1877 several thousand visitors from around the world had used the footbridge. The visitor passes ceased that September after a visitor had an epileptic seizure and nearly fell off.
As the wires were being spun, work also commenced on the demolition of buildings on either side of the river for the Brooklyn Bridge's approaches; this work was mostly complete by September 1877. The following month, initial contracts were awarded for the suspender wires, which would hang down from the main cables and support the deck. By May 1878, the main cables were more than two-thirds complete. However, the following month, one of the wires slipped, killing two people and injuring three others. In 1877, Hewitt wrote a letter urging against the use of Bessemer steel in the bridge's construction. Bids had been submitted for both crucible steel and Bessemer steel; John A. Roebling's Sons submitted the lowest bid for Bessemer steel, but at Hewitt's direction, the contract was awarded to Haigh. | Brooklyn Bridge | Wikipedia | 382 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
A subsequent investigation discovered that Haigh had substituted inferior quality wire in the cables. Of eighty rings of wire that were tested, only five met standards, and it was estimated that Haigh had earned $300,000 from the deception. At this point, it was too late to replace the cables that had already been constructed. Roebling determined that the poorer wire would leave the bridge only four times as strong as necessary, rather than six to eight times as strong. The inferior-quality wire was allowed to remain and 150 extra wires were added to each cable. To avoid public controversy, Haigh was not fired, but instead was required to personally pay for higher-quality wire. The contract for the remaining wire was awarded to the John A. Roebling's Sons, and by October 5, 1878, the last of the main cables' wires went over the river.
Nearing completion
After the suspender wires had been placed, workers began erecting steel crossbeams to support the roadway as part of the bridge's overall superstructure. Construction on the bridge's superstructure started in March 1879, but, as with the cables, the trustees initially disagreed on whether the steel superstructure should be made of Bessemer or crucible steel. That July, the trustees decided to award a contract for of Bessemer steel to the Edgemoor (or Edge Moor) Iron Works, based in Philadelphia, to be delivered by 1880. The trustees later passed another resolution for another of Bessemer steel. However, by February 1880 the steel deliveries had not started. That October, the bridge trustees questioned Edgemoor's president about the delay in steel deliveries. Despite Edgemoor's assurances that the contract would be fulfilled, the deliveries still had not been completed by November 1881. Brooklyn mayor Seth Low, who became part of the board of trustees in 1882, became the chairman of a committee tasked to investigate Edgemoor's failure to fulfill the contract. When questioned, Edgemoor's president stated that the delays were the fault of another contractor, the Cambria Iron Company, who was manufacturing the eyebars for the bridge trusses; at that point, the contract was supposed to be complete by October 1882. | Brooklyn Bridge | Wikipedia | 444 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Further complicating the situation, Washington Roebling had failed to appear at the trustees' meeting in June 1882, since he had gone to Newport, Rhode Island. After the news media discovered this, most of the newspapers called for Roebling to be fired as chief engineer, except for the Daily State Gazette of Trenton, New Jersey, and the Brooklyn Daily Eagle. Some of the longstanding trustees, including Henry C. Murphy, James S. T. Stranahan, and William C. Kingsley, were willing to vouch for Roebling, since construction progress on the Brooklyn Bridge was still ongoing. However, Roebling's behavior was considered suspect among the younger trustees who had joined the board more recently.
Construction on the bridge itself was noted in formal reports that Murphy presented each month to the mayors of New York and Brooklyn. For example, Murphy's report in August 1882 noted that the month's progress included 114 intermediate cords erected within a week, as well as 72 diagonal stays, 60 posts, and numerous floor beams, bridging trusses, and stay bars. By early 1883, the Brooklyn Bridge was considered mostly completed and was projected to open that June. Contracts for bridge lighting were awarded by February 1883, and a toll scheme was approved that March.
Opposition
There was substantial opposition to the bridge's construction from shipbuilders and merchants located to the north, who argued that the bridge would not provide sufficient clearance underneath for ships. In May 1876, these groups, led by Abraham Miller, filed a lawsuit in the United States District Court for the Southern District of New York against the cities of New York and Brooklyn.
In 1879, an Assembly Sub-Committee on Commerce and Navigation began an investigation into the Brooklyn Bridge. A seaman who had been hired to determine the height of the span, testified to the committee about the difficulties that ship masters would experience in bringing their ships under the bridge when it was completed. Another witness, Edward Wellman Serrell, a civil engineer, said that the calculations of the bridge's assumed strength were incorrect. The Supreme Court decided in 1883 that the Brooklyn Bridge was a lawful structure.
Opening | Brooklyn Bridge | Wikipedia | 432 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The New York and Brooklyn Bridge was opened for use on May 24, 1883. Thousands of people attended the opening ceremony, and many ships were present in the East River for the occasion. Officially, Emily Warren Roebling was the first to cross the bridge. The bridge opening was also attended by U.S. president Chester A. Arthur and New York mayor Franklin Edson, who crossed the bridge and shook hands with Brooklyn mayor Seth Low at the Brooklyn end. Abram Hewitt gave the principal address.
Though Washington Roebling was unable to attend the ceremony (and rarely visited the site again), he held a celebratory banquet at his house on the day of the bridge opening. Further festivity included the performance by a band, gunfire from ships, and a fireworks display. On that first day, a total of 1,800 vehicles and 150,300 people crossed the span. Less than a week after the Brooklyn Bridge opened, ferry crews reported a sharp drop in patronage, while the bridge's toll operators were processing over a hundred people a minute. However, cross-river ferries continued to operate until 1942.
The bridge had cost in 1883 dollars (about US$ in ) to build, of which Brooklyn paid two-thirds. The bonds to fund the construction would not be paid off until 1956. An estimated 27 men died during its construction. Since the New York and Brooklyn Bridge was the only bridge across the East River at that time, it was also called the East River Bridge. Until the construction of the nearby Williamsburg Bridge in 1903, the New York and Brooklyn Bridge was the longest suspension bridge in the world, 20% longer than any built previously. | Brooklyn Bridge | Wikipedia | 334 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
At the time of opening, the Brooklyn Bridge was not complete; the proposed public transit across the bridge was still being tested, while the Brooklyn approach was being completed. On May 30, 1883, six days after the opening, a woman falling down a stairway at the Brooklyn approach caused a stampede which resulted in at least twelve people being crushed and killed. In subsequent lawsuits, the Brooklyn Bridge Company was acquitted of negligence. However, the company did install emergency phone boxes and additional railings, and the trustees approved a fireproofing plan for the bridge. Public transit service began with the opening of the New York and Brooklyn Bridge Railway, a cable car service, on September 25, 1883. On May 17, 1884, one of the circus master P. T. Barnum's most famous attractions, Jumbo the elephant, led a parade of 21 elephants over the Brooklyn Bridge. This helped to lessen doubts about the bridge's stability while also promoting Barnum's circus.
1880s to 1910s
Patronage across the Brooklyn Bridge increased in the years after it opened; a million people paid to cross in the six first months. The bridge carried 8.5 million people in 1884, its first full year of operation; this number doubled to 17 million in 1885 and again to 34 million in 1889. Many of these people were cable car passengers. Additionally, about 4.5 million pedestrians a year were crossing the bridge for free by 1892.
The first proposal to make changes to the bridge was sent in only two and a half years after it opened, when Linda Gilbert suggested glass steam-powered elevators and an observatory be added to the bridge and a fee charged for use, which would in part fund the bridge's upkeep and in part fund her prison reform charity. This proposal was considered but not acted upon. Numerous other proposals were made during the first fifty years of the bridge's life. Trolley tracks were added in the center lanes of both roadways in 1898, allowing trolleys to use the bridge as well. That year, the formerly separate City of Brooklyn was unified with New York City, and the Brooklyn Bridge fell under city control. | Brooklyn Bridge | Wikipedia | 430 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Concerns about the Brooklyn Bridge's safety were raised during the turn of the century. In 1898, traffic backups due to a dead horse caused one of the truss cords to buckle. There were more significant worries after twelve suspender cables snapped in 1901, though a thorough investigation found no other defects. After the 1901 incident, five inspectors were hired to examine the bridge each day, a service that cost $250,000 a year. The Brooklyn Rapid Transit Company, which operated routes across the Brooklyn Bridge, issued a notice in 1905 saying that the bridge had reached its transit capacity.
By 1890, due to the popularity of the Brooklyn Bridge, there were proposals to construct other bridges across the East River between Manhattan and Long Island. Although a second deck for the Brooklyn Bridge was proposed, it was thought to be infeasible because doing so would overload the bridge's structural capacity. The first new bridge across the East River, the Williamsburg Bridge, opened upstream in 1903 and connected Williamsburg, Brooklyn, with the Lower East Side of Manhattan. This was followed by the Queensboro Bridge between Queens and Manhattan in March 1909, and the Manhattan Bridge between Brooklyn and Manhattan in December 1909. Several subway, railroad, and road tunnels were also constructed, which helped to accelerate the development of Manhattan, Brooklyn, and Queens.
1910s to 1940s
Though carriages and cable-car customers had paid tolls ever since the bridge's opening, pedestrians were spared from the tolls originally. By the first decade of the 20th century, pedestrians were also paying tolls. Tolls on all four bridges across the East River—the Brooklyn Bridge, as well as the Manhattan, Williamsburg, and Queensboro bridges to the north—were abolished in July 1911 as part of a populist policy initiative headed by New York City mayor William Jay Gaynor. The city government passed a bill to officially name the structure the "Brooklyn Bridge" in January 1915. | Brooklyn Bridge | Wikipedia | 386 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Ostensibly in an attempt to reduce traffic on nearby city streets, Grover Whalen, the commissioner of Plant and Structures, banned motor vehicles from the Brooklyn Bridge on July 6, 1922. The real reason for the ban was an incident the same year where two cables slipped due to high traffic loads. Both Whalen and Roebling called for the renovation of the Brooklyn Bridge and the construction of a parallel bridge, though the parallel bridge was never built. Whalen's successor William Wirt Mills announced in 1924 that a new wood-block pavement would be installed, permitting motor vehicles to use the bridge again; motor traffic was again allowed on the bridge starting on May 12, 1925.
As part of an experiment, starting in November 1946, the Manhattan-bound roadway carried Brooklyn-bound traffic during the evening rush hours. The experiment ended after two months due to complaints about congestion.
Mid- to late 20th century
Upgrades
The first major upgrade to the Brooklyn Bridge commenced in 1948, when a contract to entirely reconstruct the approach ramps was awarded to David B. Steinman. The renovation was expected to double the capacity of the bridge's roadways to nearly 6,000 cars per hour, at a projected cost of $7 million. The renovation included the demolition of both the elevated and the trolley tracks on the roadways, the removal of trusses separating the inner elevated tracks from the existing vehicle lanes and the widening of each roadway from two to three lanes, as well as the construction of a new steel-and-concrete floor. In addition, new ramps were added to Adams Street, Cadman Plaza, and the Brooklyn Queens Expressway (BQE) on the Brooklyn side, and to Park Row on the Manhattan side. The bridge was briefly closed to all traffic for the first time ever in January 1950, and the trolley tracks closed that March to allow the widening work to occur. During the construction project, one roadway at a time was closed, allowing reduced traffic flows to cross the bridge in one direction only. | Brooklyn Bridge | Wikipedia | 403 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The widened south roadway was completed in May 1951, followed by the north roadway in October 1953. The restoration was finished in May 1954 with the completion of the reconstructed elevated promenade. While the rebuilding of the span was ongoing, a fallout shelter was constructed beneath the Manhattan approach in anticipation of the Cold War. The abandoned space in one of the masonry arches was stocked with emergency survival supplies for a potential nuclear attack by the Soviet Union; these supplies remained in place half a century later. In addition, defensive barriers were added to the bridge as a safeguard against sabotage.
Simultaneous with the rebuilding of the Brooklyn Bridge, a double-decked viaduct for the BQE was being built through an existing steel overpass of the bridge's Brooklyn approach ramp. The segment of the BQE from Brooklyn Bridge south to Atlantic Avenue opened in June 1954, but the direct ramp from the northbound BQE to the Manhattan-bound Brooklyn Bridge did not open until 1959. The city also widened the Adams Street approach in Brooklyn, between the bridge and Fulton Street, from between 1954 and 1955. Subsequently, Boerum Place from Fulton Street south to Atlantic Avenue was also widened. This required the demolition of the old Kings County courthouse. The towers were cleaned in 1958 and the Brooklyn anchorage was repaired the next year.
On the Manhattan side, the city approved a controversial rebuilding of the Manhattan entrance plaza in 1953. The project, which would add a grade-separated junction over Park Row, was hotly contested because it would require the demolition of 21 structures, including the old New York World Building. The reconstruction also necessitated the relocation of 410 families on Park Row. In December 1956, the city started a two-year renovation of the plaza. This required the closure of one roadway at a time, as was done during the rebuilding of the bridge itself. Work on redeveloping the area around the Manhattan approach started in the mid-1960s. At the same time, plans were announced for direct ramps to the elevated FDR Drive to alleviate congestion at the approach. The ramp from FDR Drive to the Brooklyn Bridge was opened in 1968, followed by the ramp from the bridge to FDR Drive the next year. A single ramp from the Manhattan-bound Brooklyn Bridge to northbound Park Row was constructed in 1970. A repainting of the bridge was announced two years later in advance of its 90th anniversary.
Deterioration and late-20th century repair | Brooklyn Bridge | Wikipedia | 484 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The Brooklyn Bridge gradually deteriorated due to age and neglect. While it had 200 full-time dedicated maintenance workers before World War II, that number dropped to five by the late 20th century, and the city as a whole only had 160 bridge maintenance workers. In 1974, heavy vehicles such as vans and buses were banned from the bridge to prevent further erosion of the concrete roadway. A report in The New York Times four years later noted that the cables were visibly fraying and the pedestrian promenade had holes in it. The city began planning to replace all the Brooklyn Bridge's cables at a cost of $115 million, as part of a larger project to renovate all four toll-free East River spans. By 1980, the Brooklyn Bridge was in such dire condition that it faced imminent closure. In some places, half of the strands in the cables were broken.
In June 1981, two of the diagonal stay cables snapped, killing a pedestrian. Subsequently, the anchorages were found to have developed rust, and an emergency cable repair was necessitated less than a month later after another cable developed slack. Following the incident, the city accelerated the timetable of its proposed cable replacement, and it commenced a $153 million rehabilitation of the Brooklyn Bridge in advance of the 100th anniversary. As part of the project, the bridge's original suspender cables installed by J. Lloyd Haigh were replaced by Bethlehem Steel in 1986, marking the cables' first replacement since construction. In addition, the staircase at Washington Street in Brooklyn was renovated, the stairs from Tillary and Adams Streets were replaced with a ramp, and the short flights of steps from the promenade to each tower's balcony were removed. In a smaller project, the bridge was floodlit at night starting in 1982 to highlight its architectural features. | Brooklyn Bridge | Wikipedia | 355 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Additional problems persisted, and in 1993, high levels of lead were discovered near the bridge's towers. Further emergency repairs were undertaken in mid-1999 after small concrete shards began falling from the bridge into the East River. The concrete deck had been installed during the 1950s renovations and had a lifespan of about 60 years. The Park Row exit from the bridge's westbound lanes was closed as a safety measure after the September 11, 2001, attacks on the nearby World Trade Center. That section of Park Row had been closed off since it ran right underneath 1 Police Plaza, the headquarters of the New York City Police Department (NYPD). In early 2003, to save money on electricity, the NYCDOT turned off the bridge's "necklace lights" at night. They were turned back on later that year after several private entities made donations to fund the lights.
21st century
After the 2007 collapse of the I-35W bridge in Minneapolis, public attention focused on the condition of bridges across the U.S. The New York Times reported that the Brooklyn Bridge approach ramps had received a "poor" rating during an inspection in 2007. However, a NYCDOT spokesman said that the poor rating did not indicate a dangerous state but rather implied it required renovation. In 2010, the NYCDOT began renovating the approaches and deck, as well as repainting the suspension span. Work included widening two approach ramps from one to two lanes by re-striping a new prefabricated ramp; raising clearance over the eastbound BQE at York Street; seismic retrofitting; replacement of rusted railings and safety barriers; and road deck resurfacing. The work necessitated detours for four years. At the time, the project was scheduled to be completed in 2014; but completion was later delayed to 2015, then again to 2017. The project's cost also increased from $508 million in 2010 to $811 million in 2016. | Brooklyn Bridge | Wikipedia | 391 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
In August 2016, the NYCDOT announced that it would conduct a seven-month, $370,000 study to verify if the bridge could support a heavier upper deck that consisted of an expanded bicycle and pedestrian path. By then, about 10,000 pedestrians and 3,500 cyclists used the pathway on an average weekday. Work on the pedestrian entrance on the Brooklyn side was underway by 2017. The NYCDOT also indicated in 2016 that it planned to reinforce the Brooklyn Bridge's foundations to prevent it from sinking, as well as repair the masonry arches on the approach ramps, which had been damaged by Hurricane Sandy four years earlier. In July 2018, the New York City Landmarks Preservation Commission approved a further renovation of the Brooklyn Bridge's suspension towers and approach ramps. That December, the federal government gave the city $25 million in funding, which would pay for a $337 million rehabilitation of the bridge approaches and the suspension towers. Work started in late 2019 and was scheduled to be completed in four years. This restoration included removing bricks from the arches and putting fresh concrete behind them, using mortar from the same upstate quarries as the original mortar. The granite arches were also cleaned, revealing the original gray color of the stone, which had long been hidden by grime. Additionally, 56 LED lamps were installed on the bridge at a cost of $2.4 million.
In early 2020, City Council speaker Corey Johnson and the nonprofit Van Alen Institute hosted an international contest to solicit plans for the redesign of the bridge's walkway. Ultimately, in January 2021, the city decided to install a two-way protected bike path on the Manhattan-bound roadway, replacing the leftmost vehicular lane. The bike lane would allow the existing promenade to be used exclusively by pedestrians. Work on the bike lane started in June 2021, and the new path was completed on September 14, 2021. Despite the addition of the bike path, the bridge's walkway was still frequently overcrowded, prompting the city to propose in mid-2023 that street vendors be banned from the bridge and others citywide. All vendors were banned from the bridge at the beginning of January 2024. The same month, the bridge's new LED lights were illuminated for the first time. | Brooklyn Bridge | Wikipedia | 454 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
A plan for congestion pricing in New York City was approved in mid-2023, allowing the Metropolitan Transportation Authority to toll drivers who enter Manhattan south of 60th Street. Congestion pricing was implemented in January 2025. Most traffic to and from FDR Drive is exempt from the toll, but all other Manhattan-bound drivers pay a toll, which varies based on the time of day.
Usage
Vehicular traffic
Horse-drawn carriages have been allowed to use the Brooklyn Bridge's roadways since its opening. Originally, each of the two roadways carried two lanes of a different direction of traffic. The lanes were relatively narrow at only wide. In July 1922, motor vehicles were banned from the bridge; the ban lasted until May 1925.
After 1950, the main roadway carried six lanes of automobile traffic, three in each direction. It was then reduced to five lanes with the addition of a two-way bike lane on the Manhattan-bound side in 2021. Because of the roadway's posted height restriction of and weight restriction of , commercial vehicles and buses are prohibited from using the Brooklyn Bridge. The weight restrictions prohibit heavy passenger vehicles such as pickup trucks and SUVs from using the bridge, though this is not often enforced in practice.
On the Brooklyn side, vehicles can enter the bridge from Tillary/Adams Streets to the south, Sands/Pearl Streets to the west, and exit 28B of the eastbound Brooklyn-Queens Expressway. In Manhattan, cars can enter from both the northbound and southbound FDR Drive, as well as Park Row to the west, Chambers/Centre Streets to the north, and Pearl Street to the south. However, the exit from the bridge to northbound Park Row was closed after the September 11 attacks because of increased security concerns: that section of Park Row ran under One Police Plaza, the NYPD headquarters.
Exit list
Vehicular access to the bridge is provided by a complex series of ramps on both sides of the bridge. There are two entrances to the bridge's pedestrian promenade on either side. The current configuration was constructed from the mid-1950s up until the early 1970s. After 9/11, the ramp onto Park Row was restricted to public traffic, there are no plans to reopen it.
Rail traffic
Formerly, rail traffic operated on the Brooklyn Bridge as well. Cable cars and elevated railroads used the bridge until 1944, while trolleys ran until 1950.
Cable cars and elevated railroads | Brooklyn Bridge | Wikipedia | 483 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The New York and Brooklyn Bridge Railway, a cable car service, began operating on September 25, 1883; it ran on the inner lanes of the bridge, between terminals at the Manhattan and Brooklyn ends. Since Washington Roebling believed that steam locomotives would put excessive loads upon the structure of the Brooklyn Bridge, the cable car line was designed as a steam/cable-hauled hybrid. They were powered from a generating station under the Brooklyn approach. The cable cars could not only regulate their speed on the % upward and downward approaches, but also maintain a constant interval between each other. There were 24 cable cars in total.
Initially, the service ran with single-car trains, but patronage soon grew so much that by October 1883, two-car trains were in use. The line carried three million people in the first six months, nine million in 1884, and nearly 20 million in 1885 following the opening of the Brooklyn Union Elevated Railroad. Accordingly, the track layout was rearranged and more trains were ordered. At the same time, there were highly controversial plans to extend the elevated railroads onto the Brooklyn Bridge, under the pretext of extending the bridge itself. After disputes, the trustees agreed to build two elevated routes to the bridge on the Brooklyn side. Patronage continued to increase, and in 1888, the tracks were lengthened and even more cars were constructed to allow for four-car cable car trains. Electric wires for the trolleys were added by 1895, allowing for the potential future decommissioning of the steam/cable system. The terminals were rebuilt once more in July 1895, and, following the implementation of new electric cars in late 1896, the steam engines were dismantled and sold.
Following the unification of the cities of New York and Brooklyn in 1898, the New York and Brooklyn Bridge Railway ceased to be a separate entity that June and the Brooklyn Rapid Transit Company (BRT) assumed control of the line. The BRT started running through-services of elevated trains, which ran from Park Row Terminal in Manhattan to points in Brooklyn via the Sands Street station on the Brooklyn side. Before reaching Sands Street (at Tillary Street for Fulton Street Line trains, and at Bridge Street for Fifth Avenue Line and Myrtle Avenue Line trains), elevated trains bound for Manhattan were uncoupled from their steam locomotives. The elevated trains were then coupled to the cable cars, which would pull the passenger carriages across the bridge. | Brooklyn Bridge | Wikipedia | 483 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The BRT did not run any elevated train through services from 1899 to 1901. Due to increased patronage after the opening of the Interborough Rapid Transit Company (IRT)'s first subway line, the Park Row station was rebuilt in 1906. In the early 20th century, there were plans for Brooklyn Bridge elevated trains to run underground to the BRT's proposed Chambers Street station in Manhattan, though the connection was never opened. The overpass across William Street was closed in 1913 to make way for the proposed connection. In 1929, the overpass was reopened after it became clear that the connection would not be built.
After the IRT's Joralemon Street Tunnel and the Williamsburg Bridge tracks opened in 1908, the Brooklyn Bridge no longer held a monopoly on rail service between Manhattan and Brooklyn, and cable service ceased. New subway lines from the IRT and from the BRT's successor Brooklyn–Manhattan Transit Corporation (BMT), built in the 1910s and 1920s, posed significant competition to the Brooklyn Bridge rail services. With the opening of the Independent Subway System in 1932 and the subsequent unification of all three companies into a single entity in 1940, the elevated services started to decline, and the Park Row and Sands Street stations were greatly reduced in size. The Fifth Avenue and Fulton Street services across the Brooklyn Bridge were discontinued in 1940 and 1941 respectively, and the elevated tracks were abandoned permanently with the withdrawal of Myrtle Avenue services in 1944.
Trolleys
A plan for trolley service across the Brooklyn Bridge was presented in 1895. Two years later, the Brooklyn Bridge trustees agreed to a plan where trolleys could run across the bridge under ten-year contracts. Trolley service, which began in 1898, ran on what are now the two middle lanes of each roadway (shared with other traffic). When cable service was withdrawn in 1908, the trolley tracks on the Brooklyn side were rebuilt to alleviate congestion. Trolley service on the middle lanes continued until the elevated lines stopped using the bridge in 1944, when they moved to the protected center tracks. On March 5, 1950, the streetcars also stopped running, and the bridge was redesigned exclusively for automobile traffic.
Walkway | Brooklyn Bridge | Wikipedia | 430 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The Brooklyn Bridge has an elevated promenade open to pedestrians in the center of the bridge, located above the automobile lanes. The promenade is usually located below the height of the girders, except at the approach ramps leading to each tower's balcony. The path is generally wide, though this is constrained by obstacles such as protruding cables, benches, and stairways, which create "pinch points" at certain locations. The path narrows to at the locations where the main cables descend to the level of the promenade. Further exacerbating the situation, these "pinch points" are some of the most popular places to take pictures. As a result, in 2016, the NYCDOT announced that it planned to double the promenade's width.
A center line was painted to separate cyclists from pedestrians in 1971, creating one of the city's first dedicated bike lanes. Initially, the northern side of the promenade was used by pedestrians and the southern side by cyclists. In 2000, these were swapped, with cyclists taking the northern side and pedestrians taking the southern side. On September 14, 2021, the DOT closed off the inner-most car lane on the Manhattan-bound side with protective barriers and fencing to create a new bike path. Cyclists are now prohibited from the upper pedestrian lane.
Pedestrian access to the bridge from the Brooklyn side is from either the median of Adams Street at its intersection with Tillary Street or a staircase near Prospect Street between Cadman Plaza East and West. In Manhattan, the pedestrian walkway is accessible from crosswalks at the intersection of the bridge and Centre Street, or through a staircase leading to Park Row.
Emergency use
While the bridge has always permitted the passage of pedestrians, the promenade facilitates movement when other means of crossing the East River have become unavailable. During transit strikes by the Transport Workers Union in 1980 and 2005, people commuting to work used the bridge; they were joined by Mayors Ed Koch and Michael Bloomberg, who crossed as a gesture to the affected public. Pedestrians also walked across the bridge as an alternative to suspended subway services following the 1965, 1977, and 2003 blackouts, and after the September 11 attacks. | Brooklyn Bridge | Wikipedia | 429 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
During the 2003 blackouts, many crossing the bridge reported a swaying motion. The higher-than-usual pedestrian load caused this swaying, which was amplified by the tendency of pedestrians to synchronize their footfalls with a sway. Several engineers expressed concern about how this would affect the bridge, although others noted that the bridge did withstand the event and that the redundancies in its design—the inclusion of the three support systems (suspension system, diagonal stay system, and stiffening truss)—make it "probably the best secured bridge against such movements going out of control". In designing the bridge, John Roebling had stated that the bridge would sag but not fall, even if one of these structural systems were to fail altogether.
Notable events
Stunts
There have been several notable jumpers from the Brooklyn Bridge. The first person was Robert Emmet Odlum, brother of women's rights activist Charlotte Odlum Smith, on May 19, 1885. He struck the water at an angle and died shortly afterwards from internal injuries. Steve Brodie supposedly dropped from underneath the bridge in July 1886 and was briefly arrested for it, though there is some doubt about whether he actually jumped. Larry Donovan made a slightly higher jump from the railing a month afterward. The first known person to jump from the bridge with the intention of suicide was Francis McCarey in 1892. A lesser known early jumper was James Duffy of County Cavan, Ireland, who on April 15, 1895, asked several men to watch him jump from the bridge. Duffy jumped and was not seen again. Additionally, the cartoonist Otto Eppers jumped and survived in 1910, and was then tried and acquitted for attempted suicide. The Brooklyn Bridge has since developed a reputation as a suicide bridge due to the number of jumpers who do so intending to kill themselves, though exact statistics are difficult to find.
Other notable feats have taken place on or near the bridge. In 1919, Giorgio Pessi piloted what was then one of the world's largest airplanes, the Caproni Ca.5, under the bridge. In 1993, bridge jumper Thierry Devaux illegally performed eight acrobatic bungee jumps above the East River close to the Brooklyn tower.
Crimes and terrorism | Brooklyn Bridge | Wikipedia | 448 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
On March 1, 1994, Lebanese-born Rashid Baz opened fire on a van carrying members of the Chabad-Lubavitch Orthodox Jewish Movement, striking 16-year-old student Ari Halberstam and three others traveling on the bridge. Halberstam died five days later from his wounds, and Baz was later convicted of murder. He was apparently acting out of revenge for the Hebron massacre of Palestinian Muslims a few days prior to the incident. After initially classifying the killing as one committed out of road rage, the Justice Department reclassified the case in 2000 as a terrorist attack. The entrance ramp to the bridge on the Manhattan side was dedicated as the Ari Halberstam Memorial Ramp in 1995.
Several potential attacks or disasters have also been averted. In 1979, police disarmed a stick of dynamite placed under the Brooklyn approach, and an artist in Manhattan was arrested that year after another bombing attempt. In 2003, truck driver Iyman Faris was sentenced to about 20 years in prison for providing material support to Al-Qaeda, after an earlier plot to destroy the bridge by cutting through its support wires with blowtorches was thwarted.
Arrests
At 9:00 a.m. on May 19, 1977, artist Jack Bashkow climbed one of the towers for Bridging, a "media sculpture" by the performance group Art Corporation of America Inc. Seven artists climbed the largest bridges connected to Manhattan "to replace violence and fear in mass media for one day". When each of the artists had reached the tops of the bridges, they ignited bright-yellow flares at the same moment, resulting in rush hour traffic disruption, media attention, and the arrest of the climbers, though the charges were later dropped. Called "the first social-sculpture to use mass-media as art" by conceptual artist Joseph Beuys, the event was on the cover of the New York Post, received international attention, and received ABC Eyewitness News' 1977 Best News of the Year award. John Halpern documented the incident in the film Bridging, 1977. Halpern attempted another "bridging" "social sculpture" in 1979, when he planted a radio receiver, gunpowder and fireworks in a bucket atop one of the towers. The piece was later discovered by police, leading to his arrest for possessing a bomb. | Brooklyn Bridge | Wikipedia | 475 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
On October 1, 2011, more than 700 protesters with the Occupy Wall Street movement were arrested while attempting to march across the bridge on the roadway. Protesters disputed the police account of the events and claimed that the arrests were the result of being trapped on the bridge by the NYPD. The majority of the arrests were subsequently dismissed.
On July 22, 2014, the two American flags on the flagpoles atop each tower were found to have been replaced by bleached-white American flags. Initially, cannabis activism was suspected as a motive, but on August 12, 2014, two Berlin artists claimed responsibility for hoisting the two white flags, having switched out the original flags with their replicas. The artists said that the flags were meant to celebrate "the beauty of public space" and the anniversary of the death of German-born John Roebling, and they denied that it was an "anti-American statement".
Anniversary celebrations
The 50th-anniversary celebrations on May 24, 1933, included a ceremony featuring an airplane show, ships, and fireworks, as well as a banquet. During the centennial celebrations on May 24, 1983, a flotilla of ships visited the harbor, officials held parades, and Grucci Fireworks held a fireworks display that evening. For the centennial, the Brooklyn Museum exhibited a selection of the original drawings made for the bridge's construction, including those by Washington Roebling. Media coverage of the centennial was declared "the public relations triumph of 1983" by Inc.
The 125th anniversary of the bridge's opening was celebrated by a five-day event on May 22–26, 2008, which included a live performance by the Brooklyn Philharmonic, a special lighting of the bridge's towers, and a fireworks display. Other events included a film series, historical walking tours, information tents, a series of lectures and readings, a bicycle tour of Brooklyn, a miniature golf course featuring Brooklyn icons, and other musical and dance performances. Just before the anniversary celebrations, artist Paul St George installed the Telectroscope, a video link on the Brooklyn side of the bridge that connected to a matching device on London's Tower Bridge. A renovated pedestrian connection to Dumbo, Brooklyn, was also reopened before the anniversary celebrations. | Brooklyn Bridge | Wikipedia | 448 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Impact
At the time of construction, contemporaries marveled at what technology was capable of, and the bridge became a symbol of the era's optimism. John Perry Barlow wrote in the late 20th century of the "literal and genuinely religious leap of faith" embodied in the bridge's construction, saying that the "Brooklyn Bridge required of its builders faith in their ability to control technology".
Historical designations and plaques
The Brooklyn Bridge has been listed as a National Historic Landmark since January 29, 1964, and was subsequently added to the National Register of Historic Places on October 15, 1966. The bridge has also been a New York City designated landmark since August 24, 1967, and was designated a National Historic Civil Engineering Landmark in 1972. In addition, it was placed on UNESCO's list of tentative World Heritage Sites in 2017.
A bronze plaque is attached to the Manhattan anchorage, which was constructed on the site of the Samuel Osgood House at 1 Cherry Street in Manhattan. Named after Samuel Osgood, a Massachusetts politician and lawyer, it was built in 1770 and served as the first U.S. presidential mansion. The Osgood House was demolished in 1856.
Another plaque on the Manhattan side of the pedestrian promenade, installed by the city in 1975, indicates the bridge's status as a city landmark.
Culture
The Brooklyn Bridge has had an impact on idiomatic American English. For example, references to "selling the Brooklyn Bridge" are frequent in American culture, sometimes presented as a historical reality but more often as an expression meaning an idea that strains credulity. George C. Parker and William McCloundy were two early 20th-century con men who may have perpetrated this scam successfully, particularly on new immigrants, although the author of The Brooklyn Bridge: A Cultural History wrote, "No evidence exists that the bridge has ever been sold to a 'gullible outlander'".
As a tourist attraction, the Brooklyn Bridge is a popular site for clusters of love locks, wherein a couple inscribes a date and their initials onto a lock, attach it to the bridge, and throw the key into the water as a sign of their love. The practice is illegal in New York City and the NYPD can give violators a $100 fine. NYCDOT workers periodically remove the love locks from the bridge at a cost of $100,000 per year. | Brooklyn Bridge | Wikipedia | 479 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
To highlight the Brooklyn Bridge's cultural status, the city proposed building a Brooklyn Bridge museum near the bridge's Brooklyn end in the 1970s. Though the museum was ultimately not constructed, as many as 10,000 drawings and documents relating to it were found in a carpenter shop in Williamsburg in 1976. These documents were given to the New York City Municipal Archives, where they are normally located, though a selection of them were displayed at the Whitney Museum of American Art when they were discovered.
Media
The bridge is often featured in wide shots of the New York City skyline in television and film and has been depicted in numerous works of art. Fictional works have used the Brooklyn Bridge as a setting; for instance, the dedication of a portion of the bridge, and the bridge itself, were key components in the 2001 film Kate & Leopold. Furthermore, the Brooklyn Bridge has also served as an icon of America, with mentions in numerous songs, books, and poems. Among the most notable of these works is that of American Modernist poet Hart Crane, who used the Brooklyn Bridge as a central metaphor and organizing structure for his second book of poetry, The Bridge (1930).
The Brooklyn Bridge has also been lauded for its architecture. One of the first positive reviews was "The Bridge As A Monument", a Harper's Weekly piece written by architecture critic Montgomery Schuyler and published a week after the bridge's opening. In the piece, Schuyler wrote: "It so happens that the work which is likely to be our most durable monument, and to convey some knowledge of us to the most remote posterity, is a work of bare utility; not a shrine, not a fortress, not a palace, but a bridge." Architecture critic Lewis Mumford cited the piece as the impetus for serious architectural criticism in the U.S. He wrote that in the 1920s the bridge was a source of "joy and inspiration" in his childhood, and that it was a profound influence in his adolescence. Later critics would regard the Brooklyn Bridge as a work of art, as opposed to an engineering feat or a means of transport. Not all critics appreciated the bridge, however. Henry James, writing in the early 20th century, cited the bridge as an ominous symbol of the city's transformation into a "steel-souled machine room". | Brooklyn Bridge | Wikipedia | 467 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
The construction of the Brooklyn Bridge is detailed in numerous media sources, including David McCullough's 1972 book The Great Bridge and Ken Burns's 1981 documentary Brooklyn Bridge. It is also described in Seven Wonders of the Industrial World, a BBC docudrama series with an accompanying book, as well as Chief Engineer: Washington Roebling, The Man Who Built the Brooklyn Bridge, a biography published in 2017. | Brooklyn Bridge | Wikipedia | 82 | 47742 | https://en.wikipedia.org/wiki/Brooklyn%20Bridge | Technology | Transport infrastructure | null |
Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors. Its name signifies that transistors perform both the logic function (the first "transistor") and the amplifying function (the second "transistor"), as opposed to earlier resistor–transistor logic (RTL) and diode–transistor logic (DTL).
TTL integrated circuits (ICs) were widely used in applications such as computers, industrial controls, test equipment and instrumentation, consumer electronics, and synthesizers.
After their introduction in integrated circuit form in 1963 by Sylvania Electric Products, TTL integrated circuits were manufactured by several semiconductor companies. The 7400 series by Texas Instruments became particularly popular. TTL manufacturers offered a wide range of logic gates, flip-flops, counters, and other circuits. Variations of the original TTL circuit design offered higher speed or lower power dissipation to allow design optimization. TTL devices were originally made in ceramic and plastic dual in-line package(s) and in flat-pack form. Some TTL chips are now also made in surface-mount technology packages.
TTL became the foundation of computers and other digital electronics. Even after Very-Large-Scale Integration (VLSI) CMOS integrated circuit microprocessors made multiple-chip processors obsolete, TTL devices still found extensive use as glue logic interfacing between more densely integrated components.
History
TTL was invented in 1961 by James L. Buie of TRW, which declared it "particularly suited to the newly developing integrated circuit design technology." The original name for TTL was transistor-coupled transistor logic (TCTL). The first commercial integrated-circuit TTL devices were manufactured by Sylvania in 1963, called the Sylvania Universal High-Level Logic family (SUHL). The Sylvania parts were used in the controls of the Phoenix missile. TTL became popular with electronic systems designers after Texas Instruments introduced the 5400 series of ICs, with military temperature range, in 1964 and the later 7400 series, specified over a narrower range and with inexpensive plastic packages, in 1966. | Transistor–transistor logic | Wikipedia | 454 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
The Texas Instruments 7400 family became an industry standard. Compatible parts were made by Motorola, AMD, Fairchild, Intel, Intersil, Signetics, Mullard, Siemens, SGS-Thomson, Rifa, National Semiconductor, and many other companies, even in the Eastern Bloc (Soviet Union, GDR, Poland, Czechoslovakia, Hungary, Romania — for details see 7400 series). Not only did others make compatible TTL parts, but compatible parts were made using many other circuit technologies as well. At least one manufacturer, IBM, produced non-compatible TTL circuits for its own use; IBM used the technology in the IBM System/38, IBM 4300, and IBM 3081.
The term "TTL" is applied to many successive generations of bipolar logic, with gradual improvements in speed and power consumption over about two decades. The most recently introduced family 74Fxx is still sold today (as of 2019), and was widely used into the late 90s. 74AS/ALS Advanced Schottky was introduced in 1985. As of 2008, Texas Instruments continues to supply the more general-purpose chips in numerous obsolete technology families, albeit at increased prices. Typically, TTL chips integrate no more than a few hundred transistors each. Functions within a single package generally range from a few logic gates to a microprocessor bit-slice. TTL also became important because its low cost made digital techniques economically practical for tasks previously done by analog methods.
The Kenbak-1, ancestor of the first personal computers, used TTL for its CPU instead of a microprocessor chip, which was not available in 1971. The Datapoint 2200 from 1970 used TTL components for its CPU and was the basis for the 8008 and later the x86 instruction set. The 1973 Xerox Alto and 1981 Star workstations, which introduced the graphical user interface, used TTL circuits integrated at the level of arithmetic logic units (ALUs) and bitslices, respectively. Most computers used TTL-compatible "glue logic" between larger chips well into the 1990s. Until the advent of programmable logic, discrete bipolar logic was used to prototype and emulate microarchitectures under development.
Implementation
Fundamental TTL gate | Transistor–transistor logic | Wikipedia | 459 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
TTL inputs are the emitters of bipolar transistors. In the case of NAND inputs, the inputs are the emitters of multiple-emitter transistors, functionally equivalent to multiple transistors where the bases and collectors are tied together. The output is buffered by a common emitter amplifier.
Inputs both logical ones. When all the inputs are held at high voltage, the base–emitter junctions of the multiple-emitter transistor are reverse-biased. Unlike DTL, a small “collector” current (approximately 10 μA) is drawn by each of the inputs. This is because the transistor is in reverse-active mode. An approximately constant current flows from the positive rail, through the resistor and into the base of the multiple emitter transistor. This current passes through the base–emitter junction of the output transistor, allowing it to conduct and pulling the output voltage low (logical zero).
An input logical zero. Note that the base–collector junction of the multiple-emitter transistor and the base–emitter junction of the output transistor are in series between the bottom of the resistor and ground. If one input voltage becomes zero, the corresponding base–emitter junction of the multiple-emitter transistor is in parallel with these two junctions. A phenomenon called current steering means that when two voltage-stable elements with different threshold voltages are connected in parallel, the current flows through the path with the smaller threshold voltage. That is, current flows out of this input and into the zero (low) voltage source. As a result, no current flows through the base of the output transistor, causing it to stop conducting and the output voltage becomes high (logical one). During the transition the input transistor is briefly in its active region; so it draws a large current away from the base of the output transistor and thus quickly discharges its base. This is a critical advantage of TTL over DTL that speeds up the transition over a diode input structure.
The main disadvantage of TTL with a simple output stage is the relatively high output resistance at output logical "1" that is completely determined by the output collector resistor. It limits the number of inputs that can be connected (the fanout). Some advantage of the simple output stage is the high voltage level (up to VCC) of the output logical "1" when the output is not loaded.
Open collector wired logic | Transistor–transistor logic | Wikipedia | 510 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
A common variation omits the collector resistor of the output transistor, making an open-collector output. This allows the designer to fabricate wired logic by connecting the open-collector outputs of several logic gates together and providing a single external pull-up resistor. If any of the logic gates becomes logic low (transistor conducting), the combined output will be low. Examples of this type of gate are the 7401 and 7403 series. Open-collector outputs of some gates have a higher maximum voltage, such as 15 V for the 7426, useful when driving non-TTL loads.
TTL with a "totem-pole" output stage
To solve the problem with the high output resistance of the simple output stage the second schematic adds to this a "totem-pole" ("push–pull") output. It consists of the two n-p-n transistors V3 and V4, the "lifting" diode V5 and the current-limiting resistor R3 (see the figure on the right). It is driven by applying the same current steering idea as above.
When V2 is "off", V4 is "off" as well and V3 operates in active region as a voltage follower producing high output voltage (logical "1").
When V2 is "on", it activates V4, driving low voltage (logical "0") to the output. Again there is a current-steering effect: the series combination of V2's C-E junction and V4's B-E junction is in parallel with the series of V3 B-E, V5's anode-cathode junction, and V4 C-E. The second series combination has the higher threshold voltage, so no current flows through it, i.e. V3 base current is deprived. Transistor V3 turns "off" and it does not impact on the output.
In the middle of the transition, the resistor R3 limits the current flowing directly through the series connected transistor V3, diode V5 and transistor V4 that are all conducting. It also limits the output current in the case of output logical "1" and short connection to the ground. The strength of the gate may be increased without proportionally affecting the power consumption by removing the pull-up and pull-down resistors from the output stage. | Transistor–transistor logic | Wikipedia | 501 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
The main advantage of TTL with a "totem-pole" output stage is the low output resistance at output logical "1". It is determined by the upper output transistor V3 operating in active region as an emitter follower. The resistor R3 does not increase the output resistance since it is connected in the V3 collector and its influence is compensated by the negative feedback. A disadvantage of the "totem-pole" output stage is the decreased voltage level (no more than 3.5 V) of the output logical "1" (even if the output is unloaded). The reasons for this reduction are the voltage drops across the V3 base–emitter and V5 anode–cathode junctions.
Interfacing considerations
Like DTL, TTL is a current-sinking logic since a current must be drawn from inputs to bring them to a logic 0 voltage level. The driving stage must absorb up to 1.6 mA from a standard TTL input while not allowing the voltage to rise to more than 0.4 volts. The output stage of the most common TTL gates is specified to function correctly when driving up to 10 standard input stages (a fanout of 10). TTL inputs are sometimes simply left floating to provide a logical "1", though this usage is not recommended. | Transistor–transistor logic | Wikipedia | 272 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
Standard TTL circuits operate with a 5-volt power supply. A TTL input signal is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal, and "high" when between 2 V and VCC (5 V), and if a voltage signal ranging between 0.8 V and 2.0 V is sent into the input of a TTL gate, there is no certain response from the gate and therefore it is considered "uncertain" (precise logic levels vary slightly between sub-types and by temperature). TTL outputs are typically restricted to narrower limits of between 0.0 V and 0.4 V for a "low" and between 2.4 V and VCC for a "high", providing at least 0.4 V of noise immunity. Standardization of the TTL levels is so ubiquitous that complex circuit boards often contain TTL chips made by many different manufacturers selected for availability and cost, compatibility being assured. Two circuit board units off the same assembly line on different successive days or weeks might have a different mix of brands of chips in the same positions on the board; repair is possible with chips manufactured years later than original components. Within usefully broad limits, logic gates can be treated as ideal Boolean devices without concern for electrical limitations. The 0.4 V noise margins are adequate because of the low output impedance of the driver stage, that is, a large amount of noise power superimposed on the output is needed to drive an input into an undefined region.
In some cases (e.g., when the output of a TTL logic gate needs to be used for driving the input of a CMOS gate), the voltage level of the "totem-pole" output stage at output logical "1" can be increased closer to VCC by connecting an external resistor between the V4 collector and the positive rail. It pulls up the V5 cathode and cuts-off the diode. However, this technique actually converts the sophisticated "totem-pole" output into a simple output stage having significant output resistance when driving a high level (determined by the external resistor). | Transistor–transistor logic | Wikipedia | 443 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
Packaging
Like most integrated circuits of the period 1963–1990, commercial TTL devices are usually packaged in dual in-line packages (DIPs), usually with 14 to 24 pins, for through-hole or socket mounting. Epoxy plastic (PDIP) packages were often used for commercial temperature range components, while ceramic packages (CDIP) were used for military temperature range parts.
Beam-lead chip dies without packages were made for assembly into larger arrays as hybrid integrated circuits. Parts for military and aerospace applications were packaged in flatpacks, a form of surface-mount package, with leads suitable for welding or soldering to printed circuit boards. Today, many TTL-compatible devices are available in surface-mount packages, which are available in a wider array of types than through-hole packages.
TTL is particularly well suited to bipolar integrated circuits because additional inputs to a gate merely required additional emitters on a shared base region of the input transistor. If individually packaged transistors were used, the cost of all the transistors would discourage one from using such an input structure. But in an integrated circuit, the additional emitters for extra gate inputs add only a small area.
At least one computer manufacturer, IBM, built its own flip chip integrated circuits with TTL; these chips were mounted on ceramic multi-chip modules.
Comparison with other logic families
TTL devices consume substantially more power than equivalent CMOS devices at rest, but power consumption does not increase with clock speed as rapidly as for CMOS devices. Compared to contemporary ECL circuits, TTL uses less power and has easier design rules but is substantially slower. Designers can combine ECL and TTL devices in the same system to achieve best overall performance and economy, but level-shifting devices are required between the two logic families. TTL is less sensitive to damage from electrostatic discharge than early CMOS devices.
Due to the output structure of TTL devices, the output impedance is asymmetrical between the high and low state, making them unsuitable for driving transmission lines. This drawback is usually overcome by buffering the outputs with special line-driver devices where signals need to be sent through cables. ECL, by virtue of its symmetric low-impedance output structure, does not have this drawback. | Transistor–transistor logic | Wikipedia | 464 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
The TTL "totem-pole" output structure often has a momentary overlap when both the upper and lower transistors are conducting, resulting in a substantial pulse of current drawn from the power supply. These pulses can couple in unexpected ways between multiple integrated circuit packages, resulting in reduced noise margin and lower performance. TTL systems usually have a decoupling capacitor for every one or two IC packages, so that a current pulse from one TTL chip does not momentarily reduce the supply voltage to another.
Since the mid 1980s, several manufacturers supply CMOS logic equivalents with TTL-compatible input and output levels, usually bearing part numbers similar to the equivalent TTL component and with the same pinouts. For example, the 74HCT00 series provides many drop-in replacements for bipolar 7400 series parts, but uses CMOS technology.
Sub-types
Successive generations of technology produced compatible parts with improved power consumption or switching speed, or both. Although vendors uniformly marketed these various product lines as TTL with Schottky diodes, some of the underlying circuits, such as used in the LS family, could rather be considered DTL.
Variations of and successors to the basic TTL family, which has a typical gate propagation delay of 10ns and a power dissipation of 10 mW per gate, for a power–delay product (PDP) or switching energy of about 100 pJ, include: | Transistor–transistor logic | Wikipedia | 289 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
Low-power TTL (L), which traded switching speed (33ns) for a reduction in power consumption (1 mW) (now essentially replaced by CMOS logic)
High-speed TTL (H), with faster switching than standard TTL (6ns) but significantly higher power dissipation (22 mW)
Schottky TTL (S), introduced in 1969, which used Schottky diode clamps at gate inputs to prevent charge storage and improve switching time. These gates operated more quickly (3ns) but had higher power dissipation (19 mW)
Low-power Schottky TTL (LS) – used the higher resistance values of low-power TTL and the Schottky diodes to provide a good combination of speed (9.5 ns) and reduced power consumption (2 mW), and PDP of about 20 pJ. Probably the most common type of TTL, these were used as glue logic in microcomputers, essentially replacing the former H, L, and S sub-families.
Fast (F) and Advanced-Schottky (AS) variants of LS from Fairchild and TI, respectively, circa 1985, with "Miller-killer" circuits to speed up the low-to-high transition. These families achieved PDPs of 10 pJ and 4 pJ, respectively, the lowest of all the TTL families.
Low-voltage TTL (LVTTL) for 3.3-volt power supplies and memory interfacing.
Most manufacturers offer commercial and extended temperature ranges: for example Texas Instruments 7400 series parts are rated from 0 to 70 °C, and 5400 series devices over the military-specification temperature range of −55 to +125 °C.
Special quality levels and high-reliability parts are available for military and aerospace applications.
Radiation-hardened devices (for example from the SNJ54 series) are offered for space applications. | Transistor–transistor logic | Wikipedia | 403 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
Applications
Before the advent of VLSI devices, TTL integrated circuits were a standard method of construction for the processors of minicomputer and midrange mainframe computers, such as the DEC VAX and Data General Eclipse; however some computer families were based on proprietary components (e.g. Fairchild CTL) while supercomputers and high-end mainframes used emitter-coupled logic. They were also used for equipment such as machine tool numerical controls, printers and video display terminals, and as microprocessors became more functional for "glue logic" applications, such as address decoders and bus drivers, which tie together the function blocks realized in VLSI elements. The Gigatron TTL is a more recent (2018) example of a processor built entirely with TTL integrated circuits.
Analog applications
While originally designed to handle logic-level digital signals, a TTL inverter can be biased as an analog amplifier. Connecting a resistor between the output and the input biases the TTL element as a negative feedback amplifier. Such amplifiers may be useful to convert analog signals to the digital domain but would not ordinarily be used where analog amplification is the primary purpose. TTL inverters can also be used in crystal oscillators where their analog amplification ability is significant.
A TTL gate may operate inadvertently as an analog amplifier if the input is connected to a slowly changing input signal that traverses the unspecified region from 0.8 V to 2 V. The output can be erratic when the input is in this range. A slowly changing input like this can also cause excess power dissipation in the output circuit. If such an analog input must be used, there are specialized TTL parts with Schmitt trigger inputs available that will reliably convert the analog input to a digital value, effectively operating as a one bit A to D converter. | Transistor–transistor logic | Wikipedia | 390 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
Serial signaling
TTL serial refers to single-ended serial communication using raw transistor voltage levels: "low" for 0 and "high" for 1. UART over TTL serial is a common debug interface for embedded devices. Handheld devices such as graphing calculators and GPS receivers and fishfinders also commonly use UART with TTL. TTL serial is only a de facto standard: there are no strict electrical guidelines. Driver–receiver modules interface between TTL and longer-range serial standards: one example is the MAX232, which converts from and to RS-232.
Differential TTL is TTL serial carried over a differential pair with complement levels, providing much enhanced noise tolerance. Both RS-422 and RS-485 signals can be produced using TTL levels.
ccTalk is based on TTL voltage levels. | Transistor–transistor logic | Wikipedia | 173 | 47769 | https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor%20logic | Technology | Semiconductors | null |
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, such as a central processing unit (CPU), is called an implementation of that ISA.
In general, an ISA defines the supported instructions, data types, registers, the hardware support for managing main memory, fundamental features (such as the memory consistency, addressing modes, virtual memory), and the input/output model of implementations of the ISA.
An ISA specifies the behavior of machine code running on implementations of that ISA in a fashion that does not depend on the characteristics of that implementation, providing binary compatibility between implementations. This enables multiple implementations of an ISA that differ in characteristics such as performance, physical size, and monetary cost (among other things), but that are capable of running the same machine code, so that a lower-performance, lower-cost machine can be replaced with a higher-cost, higher-performance machine without having to replace software. It also enables the evolution of the microarchitectures of the implementations of that ISA, so that a newer, higher-performance implementation of an ISA can run software that runs on previous generations of implementations.
If an operating system maintains a standard and compatible application binary interface (ABI) for a particular ISA, machine code will run on future implementations of that ISA and operating system. However, if an ISA supports running multiple operating systems, it does not guarantee that machine code for one operating system will run on another operating system, unless the first operating system supports running machine code built for the other operating system.
An ISA can be extended by adding instructions or other capabilities, or adding support for larger addresses and data values; an implementation of the extended ISA will still be able to execute machine code for versions of the ISA without those extensions. Machine code using those extensions will only run on implementations that support those extensions.
The binary compatibility that they provide makes ISAs one of the most fundamental abstractions in computing.
Overview
An instruction set architecture is distinguished from a microarchitecture, which is the set of processor design techniques used, in a particular processor, to implement the instruction set. Processors with different microarchitectures can share a common instruction set. For example, the Intel Pentium and the AMD Athlon implement nearly identical versions of the x86 instruction set, but they have radically different internal designs. | Instruction set architecture | Wikipedia | 501 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
The concept of an architecture, distinct from the design of a specific machine, was developed by Fred Brooks at IBM during the design phase of System/360.
Some virtual machines that support bytecode as their ISA such as Smalltalk, the Java virtual machine, and Microsoft's Common Language Runtime, implement this by translating the bytecode for commonly used code paths into native machine code. In addition, these virtual machines execute less frequently used code paths by interpretation (see: Just-in-time compilation). Transmeta implemented the x86 instruction set atop VLIW processors in this fashion.
Classification of ISAs
An ISA may be classified in a number of different ways. A common classification is by architectural complexity. A complex instruction set computer (CISC) has many specialized instructions, some of which may only be rarely used in practical programs. A reduced instruction set computer (RISC) simplifies the processor by efficiently implementing only the instructions that are frequently used in programs, while the less common operations are implemented as subroutines, having their resulting additional processor execution time offset by infrequent use.
Other types include very long instruction word (VLIW) architectures, and the closely related and explicitly parallel instruction computing (EPIC) architectures. These architectures seek to exploit instruction-level parallelism with less hardware than RISC and CISC by making the compiler responsible for instruction issue and scheduling.
Architectures with even less complexity have been studied, such as the minimal instruction set computer (MISC) and one-instruction set computer (OISC). These are theoretically important types, but have not been commercialized.
Instructions
Machine language is built up from discrete statements or instructions. On the processing architecture, a given instruction may specify:
opcode (the instruction to be performed) e.g. add, copy, test
any explicit operands:
registers
literal/constant values
addressing modes used to access memory
More complex operations are built up by combining these simple instructions, which are executed sequentially, or as otherwise directed by control flow instructions.
Instruction types
Examples of operations common to many instruction sets include: | Instruction set architecture | Wikipedia | 428 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
Data handling and memory operations
Set a register to a fixed constant value.
Copy data from a memory location or a register to a memory location or a register (a machine instruction is often called move; however, the term is misleading). They are used to store the contents of a register, the contents of another memory location or the result of a computation, or to retrieve stored data to perform a computation on it later. They are often called load or store operations.
Read or write data from hardware devices.
Arithmetic and logic operations
Add, subtract, multiply, or divide the values of two registers, placing the result in a register, possibly setting one or more condition codes in a status register.
, in some ISAs, saving operand fetch in trivial cases.
Perform bitwise operations, e.g., taking the conjunction and disjunction of corresponding bits in a pair of registers, taking the negation of each bit in a register.
Compare two values in registers (for example, to see if one is less, or if they are equal).
s for arithmetic on floating-point numbers.
Control flow operations
Branch to another location in the program and execute instructions there.
Conditionally branch to another location if a certain condition holds.
Indirectly branch to another location.
Call another block of code, while saving the location of the next instruction as a point to return to.
Coprocessor instructions
Load/store data to and from a coprocessor or exchanging with CPU registers.
Perform coprocessor operations.
Complex instructions
Processors may include "complex" instructions in their instruction set. A single "complex" instruction does something that may take many instructions on other computers. Such instructions are typified by instructions that take multiple steps, control multiple functional units, or otherwise appear on a larger scale than the bulk of simple instructions implemented by the given processor. Some examples of "complex" instructions include:
transferring multiple registers to or from memory (especially the stack) at once
moving large blocks of memory (e.g. string copy or DMA transfer)
complicated integer and floating-point arithmetic (e.g. square root, or transcendental functions such as logarithm, sine, cosine, etc.)
s, a single instruction performing an operation on many homogeneous values in parallel, possibly in dedicated SIMD registers
performing an atomic test-and-set instruction or other read–modify–write atomic instruction
instructions that perform ALU operations with an operand from memory rather than a register | Instruction set architecture | Wikipedia | 509 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
Complex instructions are more common in CISC instruction sets than in RISC instruction sets, but RISC instruction sets may include them as well. RISC instruction sets generally do not include ALU operations with memory operands, or instructions to move large blocks of memory, but most RISC instruction sets include SIMD or vector instructions that perform the same arithmetic operation on multiple pieces of data at the same time. SIMD instructions have the ability of manipulating large vectors and matrices in minimal time. SIMD instructions allow easy parallelization of algorithms commonly involved in sound, image, and video processing. Various SIMD implementations have been brought to market under trade names such as MMX, 3DNow!, and AltiVec.
Instruction encoding
On traditional architectures, an instruction includes an opcode that specifies the operation to perform, such as add contents of memory to register—and zero or more operand specifiers, which may specify registers, memory locations, or literal data. The operand specifiers may have addressing modes determining their meaning or may be in fixed fields. In very long instruction word (VLIW) architectures, which include many microcode architectures, multiple simultaneous opcodes and operands are specified in a single instruction.
Some exotic instruction sets do not have an opcode field, such as transport triggered architectures (TTA), only operand(s).
Most stack machines have "0-operand" instruction sets in which arithmetic and logical operations lack any operand specifier fields; only instructions that push operands onto the evaluation stack or that pop operands from the stack into variables have operand specifiers. The instruction set carries out most ALU actions with postfix (reverse Polish notation) operations that work only on the expression stack, not on data registers or arbitrary main memory cells. This can be very convenient for compiling high-level languages, because most arithmetic expressions can be easily translated into postfix notation. | Instruction set architecture | Wikipedia | 392 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
Conditional instructions often have a predicate field—a few bits that encode the specific condition to cause an operation to be performed rather than not performed. For example, a conditional branch instruction will transfer control if the condition is true, so that execution proceeds to a different part of the program, and not transfer control if the condition is false, so that execution continues sequentially. Some instruction sets also have conditional moves, so that the move will be executed, and the data stored in the target location, if the condition is true, and not executed, and the target location not modified, if the condition is false. Similarly, IBM z/Architecture has a conditional store instruction. A few instruction sets include a predicate field in every instruction; this is called branch predication.
Number of operands
Instruction sets may be categorized by the maximum number of operands explicitly specified in instructions.
(In the examples that follow, a, b, and c are (direct or calculated) addresses referring to memory cells, while reg1 and so on refer to machine registers.)
C = A+B | Instruction set architecture | Wikipedia | 218 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
0-operand (zero-address machines), so called stack machines: All arithmetic operations take place using the top one or two positions on the stack: push a, push b, add, pop c.
C = A+B needs four instructions. For stack machines, the terms "0-operand" and "zero-address" apply to arithmetic instructions, but not to all instructions, as 1-operand push and pop instructions are used to access memory.
1-operand (one-address machines), so called accumulator machines, include early computers and many small microcontrollers: most instructions specify a single right operand (that is, constant, a register, or a memory location), with the implicit accumulator as the left operand (and the destination if there is one): load a, add b, store c.
C = A+B needs three instructions.
2-operand — many CISC and RISC machines fall under this category:
CISC — move A to C; then add B to C.
C = A+B needs two instructions. This effectively 'stores' the result without an explicit store instruction.
CISC — Often machines are limited to one memory operand per instruction: load a,reg1; add b,reg1; store reg1,c; This requires a load/store pair for any memory movement regardless of whether the add result is an augmentation stored to a different place, as in C = A+B, or the same memory location: A = A+B.
C = A+B needs three instructions.
RISC — Requiring explicit memory loads, the instructions would be: load a,reg1; load b,reg2; add reg1,reg2; store reg2,c.
C = A+B needs four instructions.
3-operand, allowing better reuse of data:
CISC — It becomes either a single instruction: add a,b,c
C = A+B needs one instruction.
CISC — Or, on machines limited to two memory operands per instruction, move a,reg1; add reg1,b,c;
C = A+B needs two instructions.
RISC — arithmetic instructions use registers only, so explicit 2-operand load/store instructions are needed: load a,reg1; load b,reg2; add reg1+reg2->reg3; store reg3,c; | Instruction set architecture | Wikipedia | 505 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
C = A+B needs four instructions.
Unlike 2-operand or 1-operand, this leaves all three values a, b, and c in registers available for further reuse.
more operands—some CISC machines permit a variety of addressing modes that allow more than 3 operands (registers or memory accesses), such as the VAX "POLY" polynomial evaluation instruction. | Instruction set architecture | Wikipedia | 80 | 47772 | https://en.wikipedia.org/wiki/Instruction%20set%20architecture | Technology | Computer architecture concepts | null |
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