Search This Blog

Monday, May 29, 2023

War of the currents

From Wikipedia, the free encyclopedia

American inventor and businessman Thomas Edison established the first investor-owned electric utility in 1882, basing its infrastructure on DC power.
 
American entrepreneur and engineer George Westinghouse introduced a rival AC-based power distribution network in 1886

The war of the currents was a series of events surrounding the introduction of competing electric power transmission systems in the late 1880s and early 1890s. It grew out of two lighting systems developed in the late 1870s and early 1880s; arc lamp street lighting running on high-voltage alternating current (AC), and large-scale low-voltage direct current (DC) indoor incandescent lighting being marketed by Thomas Edison's company. In 1886, the Edison system was faced with new competition: an alternating current system initially introduced by George Westinghouse's company that used transformers to step down from a high voltage so AC could be used for indoor lighting. Using high voltage allowed an AC system to transmit power over longer distances from more efficient large central generating stations. As the use of AC spread rapidly with other companies deploying their own systems, the Edison Electric Light Company claimed in early 1888 that high voltages used in an alternating current system were hazardous, and that the design was inferior to, and infringed on the patents behind, their direct current system.

In the spring of 1888, a media furor arose over electrical fatalities caused by pole-mounted high-voltage AC lines, attributed to the greed and callousness of the arc lighting companies that operated them. In June of that year Harold P. Brown, a New York electrical engineer, claimed the AC-based lighting companies were putting the public at risk using high-voltage systems installed in a slipshod manner. Brown also claimed that alternating current was more dangerous than direct current and tried to prove this by publicly killing animals with both currents, with technical assistance from Edison Electric. The Edison company and Brown colluded further in their parallel goals to limit the use of AC with attempts to push through legislation to severely limit AC installations and voltages. Both also colluded with Westinghouse's chief AC rival, the Thomson-Houston Electric Company, to make sure the first electric chair was powered by a Westinghouse AC generator.

By the early 1890s the war was winding down. Further deaths caused by AC lines in New York City forced electric companies to fix safety problems. Thomas Edison no longer controlled Edison Electric and subsidiary companies were beginning to add AC to the systems they were building. Mergers reduced competition between companies, including the merger of Edison Electric with their largest competitor, Thomson-Houston, forming General Electric in 1892. Edison Electric's merger with their chief alternating current rival brought an end to the war of the currents and created a new company that now controlled three quarters of the US electrical business. Westinghouse won the bid to supply electrical power for the World's Columbian Exposition in 1893 and won the major part of the contract to build Niagara Falls hydroelectric project later that year (partially splitting the contract with General Electric). DC commercial power distribution systems declined rapidly in numbers throughout the 20th century; the last DC utility in New York City was shut down in 2007.

Background

Very bright arc lighting (such as this one in 1882 New York) could only be used outdoors or in large indoor spaces where they could be mounted high out of people's sight line.

The war of the currents grew out of the development of two lighting systems; arc lighting running on alternating current and incandescent lighting running on direct current. Both were supplanting gas lighting systems, with arc lighting taking over large area/street lighting, and incandescent lighting replacing gas for business and residential indoor lighting.

Arc lighting

By the late 1870s, arc lamp systems were beginning to be installed in cities, powered by central generating plants. Arc lighting was capable of lighting streets, factory yards, or the interior of large buildings. Arc lamp systems used high voltages (above 3,000 volts) to supply current to multiple series-connected lamps, and some ran better on alternating current.

1880 saw the installation of large-scale arc lighting systems in several US cities including a central station set up by the Brush Electric Company in December 1880 to supply a 2-mile (3.2 km) length of Broadway in New York City with a 3,500–volt demonstration arc lighting system. The disadvantages of arc lighting were: it was maintenance intensive, buzzed, flickered, constituted a fire hazard, was really only suitable for outdoor lighting, and, at the high voltages used, was dangerous to work with.

Edison's DC company

Workmen burying Edison DC power lines under the streets in New York City in 1882. This costly practice played to Edison's favor in public perceptions after several deaths were caused by overhead high voltage AC lines.

In 1878 inventor Thomas Edison saw a market for a system that could bring electric lighting directly into a customer's business or home, a niche not served by arc lighting systems. By 1882 the investor-owned utility Edison Illuminating Company was established in New York City. Edison designed his utility to compete with the then established gas lighting utilities, basing it on a relatively low 110-volt direct current supply to power a high resistance incandescent lamp he had invented for the system. Edison direct current systems would be sold to cities throughout the United States, making it a standard with Edison controlling all technical development and holding all the key patents. Direct current worked well with incandescent lamps, which were the principal load of the day. Direct-current systems could be directly used with storage batteries, providing valuable load-leveling and backup power during interruptions of generator operation. Direct-current generators could be easily paralleled, allowing economical operation by using smaller machines during periods of light load and improving reliability. Edison had invented a meter to allow customers to be billed for energy proportional to consumption, but this meter worked only with direct current. Direct current also worked well with electric motors, an advantage DC held throughout the 1880s. The primary drawback with the Edison direct current system was that it ran at 110 volts from generation to its final destination giving it a relatively short useful transmission range: to keep the size of the expensive copper conductors down generating plants had to be situated in the middle of population centers and could only supply customers less than a mile from the plant.

AC transformer development in Europe

The Hungarian "ZBD" Team (Károly Zipernowsky, Ottó Bláthy, Miksa Déri). They were the inventors of the first high efficiency, closed core shunt connection transformer. The three also invented the modern power distribution system: Instead of former series connection they connect transformers that supply the appliances in parallel to the main line.

Alternating current had been under development with contributions by Guillaume Duchenne (1850s), the dynamo work of Zénobe Gramme, Ganz Works (1870s), Sebastian Ziani de Ferranti (1880s), Lucien Gaulard, and Galileo Ferraris. Starting in the 1880s alternating current gained its key advantage over direct current with the development of functional transformers that allowed the voltage to be "stepped up" to much higher transmission voltages and then dropped down to a lower end user voltage for business and residential use. The high voltages allowed a central generating station to supply a large area, up to 7-mile (11 km) long circuits.

Using induction coils to transfer power between electrical circuits had been around for 40 years with Pavel Yablochkov using them in his lighting system in 1876 and Lucien Gaulard and John Dixon Gibbs using the principle to create a "step down" transformer in 1882, but the design was not very efficient. A prototype of the high efficiency, closed core shunt connection transformer was made by the Hungarian "Z.B.D." team (composed of Károly Zipernowsky, Ottó Bláthy and Miksa Déri) at Ganz Works in 1884. The new Z.B.D. transformers were 3.4 times more efficient than the open core bipolar devices of Gaulard and Gibbs. Transformers in use today are designed based on principles discovered by the three engineers. Their patents included another major related innovation: the use of parallel connected (as opposed to series connected) power distribution. Ottó Bláthy also invented the first AC electricity meter. The reliability of this type of AC technology received impetus after the Ganz Works electrified Rome, a large metropolis, in 1886.

Westinghouse enters the AC business

Westinghouse Electric Company 1888 catalog advertising their "Alternating System".

In North America the inventor and entrepreneur George Westinghouse entered the electric lighting business in 1884 when he started to develop a DC system and hired William Stanley, Jr. to work on it. Westinghouse became aware of the new European transformer based AC systems in 1885 when he read about them in the UK technical journal Engineering. He grasped that AC combined with transformers meant greater economies of scale could be achieved with large centralized power plants transmitting stepped up voltage very long distances to be used in arc lighting as well as lower voltage home and commercial incandescent lighting supplied via a "step down" transformer at the other end. Westinghouse saw a way to build a truly competitive system instead of simply building another barely competitive DC lighting system using patents just different enough to get around the Edison patents. The Edison DC system of centralized DC plants with their short transmission range also meant there was a patchwork of un-supplied customers between Edison's plants that Westinghouse could easily supply with AC power.

William Stanley developed the first practical AC transformer for Westinghouse and helped build the first AC systems.

Westinghouse purchased the US patents rights to the Gaulard-Gibbs transformer and imported several of those as well as Siemens AC generators to begin experimenting with an AC-based lighting system in Pittsburgh. William Stanley used the Gaulard-Gibbs design and designs from the ZBD Transformer to develop the first practical transformer. The Westinghouse Electric Company was formed at the beginning of 1886. In March 1886 Stanley, with Westinghouse's backing, installed the first multiple-voltage AC power system, a demonstration incandescent lighting system, in Great Barrington, Massachusetts. Expanded to the point where it could light 23 businesses along main street with very little power loss over 4000 feet, the system used transformers to step 500 AC volts at the street down to 100 volts to power incandescent lamps at each location. By fall of 1886 Westinghouse, Stanley, and Oliver B. Shallenberger had built the first commercial AC power system in the US in Buffalo, New York.

The spread of AC

By the end of 1887 Westinghouse had 68 alternating current power stations to Edison's 121 DC-based stations. To make matters worse for Edison, the Thomson-Houston Electric Company of Lynn, Massachusetts (another competitor offering AC- and DC-based systems) had built 22 power stations. Thomson-Houston was expanding their business while trying to avoid patent conflicts with Westinghouse, arranging deals such as coming to agreements over lighting company territory, paying a royalty to use the Stanley AC transformer patent, and allowing Westinghouse to use their Sawyer-Man incandescent bulb patent. Besides Thomson-Houston and Brush there were other competitors at the time included the United States Illuminating Company and the Waterhouse Electric Light Company. All of the companies had their own electric power systems, arc lighting systems, and even incandescent lamp designs for domestic lighting, leading to constant lawsuits and patent battles between themselves and with Edison.

Safety concerns

The myriad of telephone, telegraph, and power lines over the streets of New York City in a photo of the Great Blizzard of 1888. An AC charged broken wire from the storm led to the electrocution of a boy that spring.

Elihu Thomson of Thomson-Houston was concerned about AC safety and put a great deal of effort into developing a lightning arrestor for high-tension power lines as well as a magnetic blowout switch that could shut the system down in a power surge, a safety feature the Westinghouse system did not have. Thomson also worried about what would happen with the equipment after they sold it, assuming customers would follow a risky practice of installing as many lights and generators as they could get away with. He also thought the idea of using AC lighting in residential homes was too dangerous and had the company hold back on that type of installation until a safer transformer could be developed.

Due to the hazards presented by high voltage electrical lines most European cities and the city of Chicago in the US required them to be buried underground. The City of New York did not require burying and had little in the way of regulation so by the end of 1887 the mishmash of overhead wires for telephone, telegraph, fire and burglar alarm systems in Manhattan were now mixed with haphazardly strung AC lighting system wires carrying up to 6,000 volts. Insulation on power lines was rudimentary, with one electrician referring to it as having as much value "as a molasses covered rag", and exposure to the elements was eroding it over time. A third of the wires were simply abandoned by defunct companies and slowly deteriorating, causing damage to, and shorting out the other lines. Besides being an eyesore, New Yorkers were annoyed when a large March 1888 snowstorm (the Great Blizzard of 1888) tore down a large number of the lines, cutting off utilities in the city. This spurred on the idea of having these lines moved underground but it was stopped by a court injunction obtained by Western Union. Legislation to give all the utilities 90 days to move their lines into underground conduits supplied by the city was slowly making its way through the government but that was also being fought in court by the United States Illuminating Company, who claimed their AC lines were perfectly safe.

Edison's anti-AC stance

As AC systems continued to spread into territories covered by DC systems, with the companies seeming to impinge on Edison patents including incandescent lighting, things got worse for the company. The price of copper was rising, adding to the expense of Edison's low voltage DC system, which required much heavier copper wires than higher voltage AC systems. Thomas Edison's own colleagues and engineers were trying to get him to consider AC. Edison's sales force was continually losing bids in municipalities that opted for cheaper AC systems and Edison Electric Illuminating Company president Edward Hibberd Johnson pointed out that if the company stuck with an all DC system it would not be able to do business in small towns and even mid-sized cities. Edison Electric had a patent option on the ZBD transformer, and a confidential in house report recommended that the company go AC, but Thomas Edison was against the idea.

After Westinghouse installed his first large scale system, Edison wrote in a November 1886 private letter to Edward Johnson, "Just as certain as death Westinghouse will kill a customer within six months after he puts in a system of any size, He has got a new thing and it will require a great deal of experimenting to get it working practically." Edison seemed to hold a view that the very high voltage used in AC systems was too dangerous and that it would take many years to develop a safe and workable system. Safety and avoiding the bad press of killing a customer had been one of the goals in designing his DC system and he worried that a death caused by a mis-installed AC system could hold back the use of electricity in general. Edison's understanding of how AC systems worked seemed to be extensive. He noted what he saw as inefficiencies and that, combined with the capital costs in trying to finance very large generating plants, led him to believe there would be very little cost savings in an AC venture. Edison was also of the opinion that DC was a superior system (a fact that he was sure the public would come to recognize) and inferior AC technology was being used by other companies as a way to get around his DC patents.

In February 1888 Edison Electric president Edward Johnson published an 84-page pamphlet titled "A Warning from the Edison Electric Light Company" and sent it to newspapers and to companies that had purchased or were planning to purchase electrical equipment from Edison competitors, including Westinghouse and Thomson-Houston, stating that the competitors were infringing on Edison's incandescent light and other electrical patents. It warned that purchasers could find themselves on the losing side of a court case if those patents were upheld. The pamphlet also emphasized the safety and efficiency of direct current, with the claim DC had not caused a single death, and included newspaper stories of accidental electrocutions caused by alternating current.

Execution by electricity

A June 30, 1888 Scientific American illustration of what the new electric chair might look like.

As arc lighting systems spread so did stories of how the high voltages involved were killing people, usually unwary linemen, a strange new phenomenon that seemed to instantaneously strike a victim dead. One such story in 1881 of a drunken dock worker dying after he grabbed a large electric dynamo led Buffalo, New York dentist Alfred P. Southwick to seek some application for the curious phenomenon. He worked with local physician George E. Fell and the Buffalo ASPCA, electrocuting hundreds of stray dogs, to come up with a method to euthanize animals via electricity. Southwick's 1882 and 1883 articles on how electrocution could be a replacement for hanging, using a restraint similar to a dental chair (an electric chair) caught the attention of New York State politicians who, following a series of botched hangings, were desperately seeking an alternative. An 1886 commission appointed by New York governor David B. Hill, which including Southwick, recommended in 1888 that executions be carried out by electricity using the electric chair.

There were early indications that this new form of execution would become mixed up with the war of currents. As part of their fact-finding, the commission sent out surveys to hundreds of experts on law and medicine, seeking their opinions, as well as contacting electrical experts, including Elihu Thomson and Thomas Edison. In late 1887, when death penalty commission member Southwick contacted Edison, the inventor stated he was against capital punishment and wanted nothing to do with the matter. After further prompting, Edison hit out at his chief electric power competitor, George Westinghouse, in what may have been the opening salvo in the war of currents, stating in a December 1887 letter to Southwick that it would be best to use current generated by "'alternating machines,' manufactured principally in this country by Geo. Westinghouse". Soon after the execution by electricity bill passed in June 1888, Edison was asked by a New York government official what means would be the best way to implement the state's new form of execution. "Hire out your criminals as linemen to the New York electric lighting companies" was Edison's tongue-in-cheek answer.

Anti-AC backlash

As the number of deaths attributed to high voltage lighting around the country continued to mount, a cluster of deaths in New York City in the spring of 1888 related to AC arc lighting set off a media frenzy against the "deadly arc-lighting current" and the seemingly callous lighting companies that used it. These deaths included a 15-year-old boy killed on April 15 by a broken telegraph line that had been energized with alternating current from a United States Illuminating Company line; a clerk killed two weeks later by an AC line; and a Brush Electric Company lineman killed in May by the AC line he was cutting. The press in New York seemed to switch overnight from stories about electric lights vs gas lighting to "death by wire" incidents, with each new report seeming to fan public resentment against high voltage AC and the dangerously tangled overhead electrical wires in the city.

Harold Brown's crusade

Electrical engineer Harold Pitney Brown emerged in June 1888 as an anti-AC crusader.

At this point an electrical engineer named Harold P. Brown, who at that time seemed to have no connection to the Edison company, sent a June 5, 1888 letter to the editor of the New York Post claiming the root of the problem was the alternating current (AC) system being used. Brown argued that the AC system was inherently dangerous and "damnable" and asked why the "public must submit to constant danger from sudden death" just so utilities could use a cheaper AC system.

At the beginning of attacks on AC, Westinghouse, in a June 7, 1888 letter, tried to defuse the situation. He invited Edison to visit him in Pittsburgh and said "I believe there has been a systemic attempt on the part of some people to do a great deal of mischief and create as great a difference as possible between the Edison Company and The Westinghouse Electric Co., when there ought to be an entirely different condition of affairs". Edison thanked him but said "My laboratory work consumes the whole of my time".

On June 8, Brown was lobbying in person before the New York Board of Electrical Control, asking that his letter to the paper be read into the meeting's record and demanding severe regulations on AC including limiting voltage to 300 volts, a level that would make AC next to useless for transmission. There were many rebuttals to Brown's claims in the newspapers and letters to the board, with people pointing out he was showing no scientific evidence that AC was more dangerous than DC. Westinghouse pointed out in letters to various newspapers the number of fires caused by DC equipment and suggested that Brown was obviously being controlled by Edison, something Brown continually denied.

A July edition of The Electrical Journal covered Brown's appearance before the New York Board of Electrical Control and the debate in technical societies over the merits of DC and AC and noted that:

The battle of the currents is being fought this week in New York.

At a July meeting Board of Electrical Control, Brown's criticisms of AC and even his knowledge of electricity was challenged by other electrical engineers, some of whom worked for Westinghouse. At this meeting, supporters of AC provided anecdotal stories from electricians on how they had survived shocks from AC at voltages up to 1000 volts and argued that DC was the more dangerous of the two.

Brown's demonstrations

Brown, determined to prove alternating current was more dangerous than direct current, at some point contacted Thomas Edison to see if he could make use of equipment to conduct experiments. Edison immediately offered to assist Brown in his crusade against AC companies. Before long, Brown was loaned space and equipment at Edison's West Orange, New Jersey laboratory, as well as laboratory assistant Arthur Kennelly.

Brown paid local children to collect stray dogs off the street for his experiments with direct and alternating current. After much experimentation killing a series of dogs, Brown held a public demonstration on July 30 in a lecture room at Columbia College. With many participants shouting for the demonstration to stop and others walking out, Brown subjected a caged dog to several shocks with increasing levels of direct current up to 1,000 volts, which the dog survived. Brown then applied 330 volts of alternating current which killed the dog. Four days later he held a second demonstration to answer critics' claims that the DC probably weakened the dog before it died. In this second demonstration, three dogs were killed in quick succession with 300 volts of AC. Brown wrote to a colleague that he was sure this demonstration would get the New York Board of Electrical Control to limit AC installations to 300 volts. Brown's campaign to restrict AC to 300 volts was unsuccessful but legislation did come close to passing in Ohio and Virginia.

Collusion with Edison

What brought Brown to the forefront of the debate over AC and his motives remain unclear, but historians note there grew to be some form of collusion between the Edison company and Brown. Edison records seem to show it was Edison Electric Light treasurer Francis S. Hastings who came up with the idea of using Brown and several New York physicians to attack Westinghouse and the other AC companies in retaliation for what Hastings thought were unscrupulous bids by Westinghouse for lighting contracts in Denver and Minneapolis. Hasting brought Brown and Edison together and was in continual contact with Brown. Edison Electric seemed to be footing the bill for some of Brown's publications on the dangers of AC. In addition, Thomas Edison himself sent a letter to the city government of Scranton, Pennsylvania recommending Brown as an expert on the dangers of AC. Some of this collusion was exposed in letters stolen from Brown's office and published in August 1889.

Patents and mergers

Nikola Tesla's induction motor patent was acquired by Westinghouse in July 1888 with plans to incorporate it in a completely integrated AC system.

During this period Westinghouse continued to pour money and engineering resources into the goal of building a completely integrated AC system. To gain control of the Sawyer-Man lamp patents he bought Consolidated Electric Light in 1887. He bought the Waterhouse Electric Light Company in 1888 and the United States Illuminating Company in 1890, giving Westinghouse their own arc lighting systems as well as control over all the major incandescent lamp patents not controlled by Edison. In April 1888 Westinghouse engineer Oliver B. Shallenberger developed an induction meter that used a rotating magnetic field for measuring alternating current, giving the company a way to calculate how much electricity a customer used. In July 1888 Westinghouse paid a substantial amount to license Nikola Tesla's US patents for a poly-phase AC induction motor and obtained a patent option on Galileo Ferraris' induction motor design. Although the acquisition of a feasible AC motor gave Westinghouse a key patent in building a completely integrated AC system, the general shortage of cash the company was going through by 1890 meant development had to be put on hold for a while. The difficulties of obtaining funding for such a capital intensive business was becoming a serious problem for the company and 1890 saw the first of several attempts by investor J. P. Morgan to take over Westinghouse Electric.

Thomson-Houston was continuing to expand, buying seven smaller electric companies including a purchase of the Brush Electric Company in 1889. By 1890 Thomson-Houston controlled the majority of the arc lighting systems in the US and a collection of its own US AC patents. Several of the business deals between Thomson-Houston and Westinghouse fell apart and in April 1888 a judge rolled back part of Westinghouse's original Gaulard Gibbs patent, stating it only covered transformers linked in series.

With the help of the financier Henry Villard the Edison group of companies also went through a series of mergers: Edison Lamp Company, a lamp manufacturer in East Newark, New Jersey; Edison Machine Works, a manufacturer of dynamos and large electric motors in Schenectady, New York; Bergmann & Company, a manufacturer of electric lighting fixtures, sockets, and other electric lighting devices; and Edison Electric Light Company, the patent-holding company and the financial arm backed by J.P. Morgan and the Vanderbilt family for Edison's lighting experiments, merged. The new company, Edison General Electric Company, was formed in January 1889 with the help of Drexel, Morgan & Co. and Grosvenor Lowrey with Villard as president. It later included the Sprague Electric Railway & Motor Company.

The peak of the war

Through the fall of 1888 a battle of words with Brown specifically attacking Westinghouse continued to escalate. In November George Westinghouse challenged Brown's assertion in the pages of the Electrical Engineer that the Westinghouse AC systems had caused 30 deaths. The magazine investigated the claim and found at most only two of the deaths could be attributed to Westinghouse installations.

Associating AC and Westinghouse with the electric chair

Although New York had a criminal procedure code that specified electrocution via an electric chair, it did not spell out the type of electricity, the amount of current, or its method of supply, since these were still relative unknowns. The New York Medico-Legal Society, an informal society composed of doctors and lawyers, was given the task of working out the details and in late 1888 through early 1889 conducted a series of animal experiments on voltage amounts, electrode design and placement, and skin conductivity. During this time they sought the advice of Harold Brown as a consultant. This ended up expanding the war of currents into the development of the chair and the general debate over capital punishment in the US.

After the Medico-Legal Society formed their committee in September 1888 chairman Frederick Peterson, who had been an assistant at Brown's July 1888 public electrocution of dogs with AC at Columbia College, had the results of those experiments submitted to the committee. The claims that AC was more deadly than DC and was the best current to use was questioned with some committee members pointing out that Brown's experiments were not scientifically carried out and were on animals smaller than a human being. At their November meeting the committee recommended 3000 volts although the type of electricity, direct current or alternating current, was not determined.

Harold Brown demonstrating the killing power of AC to the New York Medico-Legal Society by electrocuting a horse at Thomas Edison's West Orange laboratory.

In order to more conclusively prove to the committee that AC was more deadly than DC, Brown contacted Edison Electric Light treasurer Francis S. Hastings to arrange the use of the West Orange laboratory. There on December 5, 1888 Brown set up an experiment with members of the press, members of the Medico-Legal Society, the chairman of the death penalty commission, and Thomas Edison looking on. Brown used alternating current for all of his tests on animals larger than a human, including 4 calves and a lame horse, all dispatched with 750 volts of AC. Based on these results the Medico-Legal Society's December meeting recommended the use of 1000–1500 volts of alternating current for executions and newspapers noted the AC used was half the voltage used in the power lines over the streets of American cities.

Westinghouse criticized these tests as a skewed self-serving demonstration designed to be a direct attack on alternating current. On December 13 in a letter to the New York Times, Westinghouse spelled out where Brown's experiments were wrong and claimed again that Brown was being employed by the Edison company. Brown's December 18 letter refuted the claims and Brown even challenged Westinghouse to an electrical duel, with Brown agreeing to be shocked by ever-increasing amounts of DC power if Westinghouse submitted himself to the same amount of increasing AC power, first to quit loses. Westinghouse declined the offer.

In March 1889 when members of the Medico-Legal Society embarked on another series of tests to work out the details of electrode composition and placement they turned to Brown for technical assistance. Edison treasurer Hastings tried unsuccessfully to obtain a Westinghouse AC generator for the test. They ended up using Edison's West Orange laboratory for the animal tests.

Also in March, Superintendent of Prisons Austin Lathrop asked Brown if he could supply the equipment needed for the executions as well as design the electric chair. Brown turned down the job of designing the chair but did agree to fulfill the contract to supply the necessary electrical equipment. The state refused to pay up front, and Brown apparently turned to Edison Electric as well as Thomson-Houston Electric Company to help obtaining the equipment. This became another behind-the-scenes maneuver to acquire Westinghouse AC generators to supply the current, apparently with the help of the Edison company and Westinghouse's chief AC rival, Thomson-Houston. Thomson-Houston arranged to acquire three Westinghouse AC generators by replacing them with new Thomson-Houston AC generators. Thomson-Houston president Charles Coffin had at least two reasons for obtaining the Westinghouse generators; he did not want his company's equipment to be associated with the death penalty and he wanted to use one to prove a point, paying Brown to set up a public efficiency test to show that Westinghouse's sales claim of manufacturing 50% more efficient generators was false.

That spring Brown published "The Comparative Danger to Life of the Alternating and Continuous Electrical Current" detailing the animal experiments done at Edison's lab and claiming they showed AC was far deadlier than DC. This 61-page professionally printed booklet (probably paid for by the Edison company) was sent to government officials, newspapers, and businessmen in towns with populations greater than 5000 inhabitants.

In May 1889 when New York had its first criminal sentenced to be executed in the electric chair, a street merchant named William Kemmler, there was a great deal of discussion in the editorial column of the New York Times as to what to call the then-new form of execution. The term "Westinghoused" was put forward as well as "Gerrycide" (after death penalty commission head Elbridge Gerry), and "Browned". The Times hated the word that was eventually adopted, electrocution, describing it as being pushed forward by "pretentious ignoramuses". One of Edison's lawyers wrote to his colleague expressing an opinion that Edison's preference for dynamort, ampermort and electromort were not good terms but thought Westinghoused was the best choice.

The Kemmler appeal

After William Kemmler was sentenced to death in the electric chair his appeal was financed by Westinghouse, an attempt to prevent Westinghouse AC generators from being used in an execution, by repealing the electrocution law.

William Kemmler was sentenced to die in the electric chair around June 24, 1889, but before the sentence could be carried out an appeal was filed on the grounds that it constituted cruel and unusual punishment under the U.S. Constitution. It became obvious to the press and everyone involved that the politically connected (and expensive) lawyer who filed the appeal, William Bourke Cockran, had no connection to the case but did have connection to the Westinghouse company, obviously paying for his services.

During fact-finding hearings held around the state beginning on July 9 in New York City, Cockran used his considerable skills as a cross-examiner and orator to attack Brown, Edison, and their supporters. His strategy was to show that Brown had falsified his test on the killing power of AC and to prove that electricity would not cause certain death and simply lead to torturing the condemned. In cross examination he questioned Brown's lack of credentials in the electrical field and brought up possible collusion between Brown and Edison, which Brown again denied. Many witnesses were called by both sides to give firsthand anecdotal accounts about encounters with electricity and evidence was given by medical professionals on the human body's nervous system and the electrical conductivity of skin. Brown was accused of fudging his tests on animals, hiding the fact that he was using lower current DC and high-current AC. When the hearing convened for a day at Edison's West Orange lab to witness demonstrations of skin resistance to electricity, Brown almost got in a fight with a Westinghouse representative, accusing him of being in the Edison laboratory to conduct industrial espionage. Newspapers noted the often contradictory testimony was raising public doubts about the electrocution law but after Edison took the stand many accepted assurances from the "wizard of Menlo Park" that 1000 volts of AC would easily kill any man.

After the gathered testimony was submitted and the two sides presented their case, Judge Edwin Day ruled against Kemmler's appeal on October 9 and US Supreme Court denied Kemmler's appeal on May 23, 1890.

When the chair was first used, on August 6, 1890, the technicians on hand misjudged the voltage needed to kill William Kemmler. After the first jolt of electricity Kemmler was found to be still breathing. The procedure had to be repeated and a reporter on hand described it as "an awful spectacle, far worse than hanging." George Westinghouse commented: "They would have done better using an axe."

Brown's collusion exposed

On August 25, 1889 the New York Sun ran a story headlined:

"For Shame, Brown! – Disgraceful Facts About the Electric Killing Scheme; Queer Work for a State's Expert; Paid by One Electric Company to Injure Another"

The story was based on 45 letters stolen from Brown's office that spelled out Brown's collusion with Thomson-Houston and Edison Electric. The majority of the letters were correspondence between Brown and Thomson-Houston on the topic of acquiring the three Westinghouse generators for the state of New York as well as using one of them in an efficiency test. They also showed that Brown had received $5,000 from Edison Electric to purchase the surplus Westinghouse generators from Thomson-Houston. Further Edison involvement was contained in letters from Edison treasurer Hastings asking Brown to send anti-AC pamphlets to all the legislators in the state of Missouri (at the company's expense), Brown requesting that a letter of recommendation from Thomas Edison be sent to Scranton, PA, as well as Edison and Arthur Kennelly coaching Brown in his upcoming testimony in the Kemmler appeal trial.

Brown was not slowed down by this revelation and characterized his efforts to expose Westinghouse as the same as going after a grocer who sells poison and calls it sugar.

The "Electric Wire Panic"

The death of Western Union Lineman John Feeks led to laws finally being passed to move AC lines underground in New York City.

1889 saw another round of deaths attributed to alternating current including a lineman in Buffalo, New York, four linemen in New York City, and a New York fruit merchant who was killed when the display he was using came in contact with an overhead line. NYC Mayor Hugh J. Grant, in a meeting with the Board of Electrical Control and the AC electric companies, rejected the claims that the AC lines were perfectly safe saying "we get news of all who touch them through the coroners office" On October 11, 1889, John Feeks, a Western Union lineman, was high up in the tangle of overhead electrical wires working on what were supposed to be low-voltage telegraph lines in a busy Manhattan district. As the lunchtime crowd below looked on he grabbed a nearby line that, unknown to him, had been shorted many blocks away with a high-voltage AC line. The jolt entered through his bare right hand and exited his left steel studded climbing boot. Feeks was killed almost instantly, his body falling into the tangle of wire, sparking, burning, and smoldering for the better part of an hour while a horrified crowd of thousands gathered below. The source of the power that killed Feeks was not determined although United States Illuminating Company lines ran nearby.

Feeks' public death sparked a new round of people fearing the electric lines over their heads in what has been called the "Electric Wire Panic". The blame seemed to settle on Westinghouse since, Westinghouse having bought many of the lighting companies involved, people assumed Feeks' death was the fault of a Westinghouse subsidiary. Newspapers joined into the public outcry following Feeks' death, pointing out men's lives "were cheaper to this monopoly than insulated wires" and calling for the executives of AC companies to be charged with manslaughter. The October 13, 1889, New Orleans Times-Picayune noted "Death does not stop at the door, but comes right into the house, and perhaps as you are closing a door or turning on the gas you are killed." Harold Brown's reputation was rehabilitated almost overnight with newspapers and magazines seeking his opinion and reporters following him around New York City where he measured how much current was leaking from AC power lines.

The death of Feeks marked the first time Edison publicly denounced alternating current.

At the peak of the war of currents, Edison himself joined the public debate for the first time, denounced AC current in a November 1889 article in the North American Review titled "The Dangers of Electric Lighting". Edison put forward the view that burying the high-voltage lines was not a solution, and would simply move the deaths underground and be a "constant menace" that could short with other lines threatening people's homes and lives. He stated the only way to make AC safe was to limit its voltage and vowed Edison Electric would never adopt AC as long as he was in charge.

George Westinghouse was suddenly put in the role of a villain trying to defend pole-mounted AC installations that he knew were unsafe and fumbled at reporters' questions trying to point out all the other things in a large city that were more dangerous. The next month he did better in his response printed in the North American Review, pointing out that his AC/transformer system actually used lower household voltages than the Edison DC system. He also pointed out 87 deaths in one year caused by street cars and gas lighting versus only 5 accidental electrocutions and no in-home deaths attributed to AC current.

The crowd that watched Feeks contained many New York aldermen due to the site of the accident being near the New York government offices and the horrifying affair galvanized them into the action of passing the law on moving utilities underground. The electric companies involved obtained an injunction preventing their lines from being cut down immediately but shut down most of their lighting until the situation was settled, plunging many New York streets into darkness. The legislation ordering the cutting down of all of the utility lines was finally upheld by the New York Supreme Court in December. The AC lines were cut down keeping many New York City streets in darkness for the rest of the winter since little had been done by the overpaid Tammany Hall city supervisors who were supposed to see to building the underground "subways" to house them.

The current war ends

Even with the Westinghouse propaganda losses, the war of currents itself was winding down with direct current on the losing side. This was due in part to Thomas Edison himself leaving the electric power business. Edison was becoming marginalized in his own company having lost majority control in the 1889 merger that formed Edison General Electric. In 1890 he told president Henry Villard he thought it was time to retire from the lighting business and moved on to an iron ore refining project that preoccupied his time. Edison's dogmatic anti-AC values were no longer controlling the company. By 1889 Edison's Electric's own subsidiaries were lobbying to add AC power transmission to their systems and in October 1890 Edison Machine Works began developing AC-based equipment.

With Thomas Edison no longer involved with Edison General Electric, the war of currents came to a close with a financial merger. Edison president Henry Villard, who had engineered the merger that formed Edison General Electric, was continually working on the idea of merging that company with Thomson-Houston or Westinghouse. He saw a real opportunity in 1891. The market was in a general downturn causing cash shortages for all the companies concerned and Villard was in talks with Thomson-Houston, which was now Edison General Electric's biggest competitor. Thomson-Houston had a habit of saving money on development by buying, or sometimes stealing, patents. Patent conflicts were stymieing the growth of both companies and the idea of saving on some 60 ongoing lawsuits as well as saving on profit losses of trying to undercut each other by selling generating plants below cost pushed forward the idea of this merger in financial circles. Edison hated the idea and tried to hold it off but Villard thought his company, now winning its incandescent light patent lawsuits in the courts, was in a position to dictate the terms of any merger. As a committee of financiers, which included J.P. Morgan, worked on the deal in early 1892 things went against Villard. In Morgan's view Thomson-Houston looked on the books to be the stronger of the two companies and engineered a behind the scenes deal announced on April 15, 1892, that put the management of Thomson-Houston in control of the new company, now called General Electric (dropping Edison's name). Thomas Edison was not aware of the deal until the day before it happened.

The fifteen electric companies that existed five years before had merged down to two; General Electric and Westinghouse. The war of currents came to an end and this merger of the Edison company, along with its lighting patents, and the Thomson-Houston, with its AC patents, created a company that controlled three quarters of the US electrical business. From this point on General Electric and Westinghouse were both marketing alternating current systems. Edison put on a brave face noting to the media how his stock had gained value in the deal but privately he was bitter that his company and all of his patents had been turned over to the competition.

Aftermath

Even though the institutional war of currents had ended in a financial merger, the technical difference between direct and alternating current systems followed a much longer technical merger. Due to innovation in the US and Europe, alternating current's economy of scale with very large generating plants linked to loads via long-distance transmission was slowly being combined with the ability to link it up with all of the existing systems that needed to be supplied. These included single phase AC systems, poly-phase AC systems, low voltage incandescent lighting, high voltage arc lighting, and existing DC motors in factories and street cars. In the engineered universal system these technological differences were temporarily being bridged via the development of rotary converters and motor–generators that allowed the large number of legacy systems to be connected to the AC grid. These stopgaps were slowly replaced as older systems were retired or upgraded.

In May 1892 Westinghouse Electric managed to underbid General Electric on the contract to electrify the World's Columbian Exposition in Chicago and, although they made no profit, their demonstration of a safe and effective highly flexible universal alternating current system powering all of the disparate electrical systems at the Exposition led to them winning the bid at the end of that year to build an AC power station at Niagara Falls. General Electric was awarded contracts to build AC transmission lines and transformers in that project and further bids at Niagara were split with GE who were quickly catching up in the AC field due partly to Charles Proteus Steinmetz, a Prussian mathematician who was the first person to fully understand AC power from a solid mathematical standpoint. General Electric hired many talented new engineers to improve its design of transformers, generators, motors and other apparatusA three-phase three-wire transmission system had already been deployed in Europe at the International Electro-Technical Exhibition of 1891, where Mikhail Dolivo-Dobrovolsky used this system to transmit electric power over a distance of 176 km with 75% efficiency. In 1891 he also created a three-phase transformer, the short-circuited (squirrel-cage) induction motor and designed the world's first three-phase hydroelectric power plant.

Patent lawsuits were still hampering both companies and bleeding off cash, so in 1896, J. P. Morgan engineered a patent sharing agreement between the two companies that remained in force for 11 years.

In 1897 Edison sold his remaining stock in Edison Electric Illuminating of New York to finance his iron ore refining prototype plant. In 1908 Edison said to George Stanley, son of AC transformer inventor William Stanley, Jr., "Tell your father I was wrong", probably admitting he had underestimated the developmental potential of alternating current.

Remnant and existent DC systems

Some cities continued to use DC well into the 20th century. For example, central Helsinki had a DC network until the late 1940s, and Stockholm lost its dwindling DC network as late as the 1970s. A mercury-arc valve rectifier station could convert AC to DC where networks were still used. Parts of Boston, Massachusetts, along Beacon Street and Commonwealth Avenue still used 110 volts DC in the 1960s, causing the destruction of many small appliances (typically hair dryers and phonographs) used by Boston University students, who ignored warnings about the electricity supply.

New York City's electric utility company, Consolidated Edison, continued to supply direct current to customers who had adopted it early in the twentieth century, mainly for elevators. The New Yorker Hotel, constructed in 1929, had a large direct-current power plant and did not convert fully to alternating-current service until well into the 1960s. This was the building in which AC pioneer Nikola Tesla spent his last years, and where he died in 1943. New York City's Broadway theaters continued to use DC services until 1975, requiring the use of outmoded manual resistance dimmer boards operated by several stagehands. This practice ended when the musical A Chorus Line introduced computerized lighting control and thyristor (SCR) dimmers to Broadway, and New York theaters were finally converted to AC.

In January 1998, Consolidated Edison started to eliminate DC service. At that time there were 4,600 DC customers. By 2006, there were only 60 customers using DC service, and on November 14, 2007, the last direct-current distribution by Con Edison was shut down. Customers still using DC were provided with on-site AC to DC rectifiers. Pacific Gas and Electric Company still provides DC power to some locations in San Francisco, primarily for elevators, supplied by close to 200 rectifiers each providing power for 7–10 customers.

The Central Electricity Generating Board in the UK maintained a 200–volt DC generating station at Bankside Power Station in London until 1981. It exclusively powered DC printing machinery in Fleet Street, then the heart of the UK's newspaper industry. It was decommissioned later in 1981 when the newspaper industry moved into the developing docklands area further down the river (using modern AC-powered equipment).

High-voltage direct current (HVDC) systems are used for bulk transmission of energy from distant generating stations, for underwater lines, and for interconnection of separate alternating-current systems.

Diesel generator

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Diesel_generator

A Cummins diesel generator of 150 kVA temporarily parked in a tourist resort in Egypt.
 
A 200 kW Caterpillar diesel generator set in a sound attenuated enclosure used as emergency backup at a sewage treatment substation in Atlanta, United States.

A diesel generator (DG) (also known as a diesel genset) is the combination of a diesel engine with an electric generator (often an alternator) to generate electrical energy. This is a specific case of engine generator. A diesel compression-ignition engine is usually designed to run on diesel fuel, but some types are adapted for other liquid fuels or natural gas.

Diesel generating sets are used in places without connection to a power grid, or as an emergency power supply if the grid fails, as well as for more complex applications such as peak-lopping, grid support, and export to the power grid.

Diesel generator size is crucial to minimize low load or power shortages. Sizing is complicated by the characteristics of modern electronics, specifically non-linear loads. In size ranges around 50 MW and above, an open cycle gas turbine is more efficient at full load than an array of diesel engines, and far more compact, with comparable capital costs; but for regular part-loading, even at these power levels, diesel arrays are sometimes preferred to open cycle gas turbines, due to their superior efficiencies.

Diesel generator set

Diesel generator on an oil tanker.

The packaged combination of a diesel engine, a generator, and various ancillary devices (such as base, canopy, sound attenuation, control systems, circuit breakers, jacket water heaters, and starting system) is referred to as a "generating set" or a "genset" for short.

Set sizes range from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops, and offices, with the larger industrial generators from 8 kW (11 kVA) up to 2,000 kW (2,500 kVA three phase) used for office complexes, factories, and other industrial facilities. A 2,000 kW set can be housed in a 40 ft (12 m) ISO container with a fuel tank, controls, power distribution equipment and all other equipment needed to operate as a standalone power station or as a standby backup to grid power. These units, referred to as power modules, are gensets on large triple axle trailers weighing 85,000 pounds (38,555 kg) or more. A combination of these modules are used for small power stations and these may use from one to 20 units per power section, these sections can be combined to involve hundreds of power modules. In these larger sizes, the power module (engine and generator) are brought to site on trailers separately and are connected with large cables and a control cable to form a complete synchronized power plant. A number of options also exist to tailor specific needs, including control panels for autostart and mains paralleling, acoustic canopies for fixed or mobile applications, ventilation equipment, fuel supply systems, exhaust systems, etc.

Diesel generators are not only for emergency power, but may also have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators. In the UK, this program is run by the national grid and is called STOR.

Ships often also employ diesel generators, sometimes not only to provide auxiliary power for lights, fans, winches etc., but also indirectly for main propulsion. With electric propulsion ,the generators can be placed in a convenient position, to allow more cargo to be carried. Electric drives for ships were developed before World War I. Electric drives were specified in many warships built during World War II because manufacturing capacity for large reduction gears was in short supply, compared to capacity for manufacture of electrical equipment. Such a diesel-electric arrangement is also used in some very large land vehicles, such as railroad locomotives.

Generator size

Generating sets are selected based on the electrical load they are intended to supply, the electrical load's characteristics such as kW, kVA, var, harmonic content, surge currents (e.g., motor starting current) and non-linear loads. The expected duty (such as emergency, prime or continuous power)as well as environmental conditions (such as altitude, temperature, and exhaust emissions regulations) must also be considered.

Most of the larger generator set manufacturers offer software that will perform the complicated sizing calculations by simply inputting site conditions and connected electrical load characteristics.

Power plants – electrical "island" mode

One or more diesel generators operating without a connection to an electrical grid are referred to as operating in island mode. Operating generators in parallel provides the advantage of redundancy and can provide better efficiency at partial loads. The plant brings generator sets online and takes them offline depending on the demands of the system at a given time. An islanded power plant intended for a primary power source of an isolated community will often have at least three diesel generators, any two of which are rated to carry the required load. Groups of up to 20 are not uncommon.

Generators can be electrically connected through the process of synchronization. Synchronization involves matching voltage, frequency, and phase before connecting the generator to the system. Failure to synchronize before connection, could cause a high short circuit current or wear and tear on the generator or its switchgear. The synchronization process can be done automatically by an auto-synchronizer module, or manually by the instructed operator. The auto-synchronizer will read the voltage, frequency and phase parameters from the generator and busbar voltages, while regulating the speed through the engine governor or ECM (Engine Control Module).

The load can be shared among parallel running generators through load sharing. Load sharing can be achieved by using droop speed control controlled by the frequency at the generator, while it constantly adjusts the engine fuel control to shift load to and from the remaining power sources. A diesel generator will take more load when the fuel supply to its combustion system is increased, while load is released if the fuel supply is decreased.

Supporting main utility grids

In addition to their well known role as power supplies during power failures, diesel generator sets also routinely support main power grids worldwide in two distinct ways:

Grid support

Emergency standby diesel generators, such as those used in hospitals and water plants, are, as a secondary function, widely used in the US and, in the recent past, in Great Britain to support the respective national grids at times for a variety of reasons. In the UK the tenders known as the Short Term Operating Reserve have exhibited quite variable prices, and from 2012 the volume of demand-side participation, which mainly entails the use of on-site diesels, has dropped as the tendered prices fell. Some 0.5 GWe of diesels have at times been used to support the National Grid, whose peak load is about 60 GW. These are sets in the size range of 200 kW to 2 MW. This usually occurs during, for example, the sudden loss of a large conventional 660 MW plant, or a sudden unexpected rise in power demand eroding the normal spinning reserve available.

This is beneficial for both parties - the diesels have already been purchased for other reasons; but to be reliable need to be fully load tested. Grid paralleling is a convenient way of doing this. This method of operation is normally undertaken by a third-party aggregator who manages the operation of the generators and the interaction with the system operator.

These diesels can in some cases be up and running in parallel as quickly as two minutes, with no impact on the site (the office or factory need not shut down). This is far quicker than a base load power station which can take 12 hours from cold, and faster than a gas turbine, which can take several minutes. Whilst diesels are very expensive in fuel terms, they are only used a few hundred hours per year in this duty, and their availability can prevent the need for a base load station running inefficiently at part load continuously. The diesel fuel used is the fuel that would have been used in testing anyway.

In Great Britain, National Grid can generally rely upon about 2 GW of customer demand reduction via back-up diesels being self-dispatched for about 10 to 40 hours a year at times of expected peak national demand. National Grid does not control these diesels - they are run by the customer to avoid "triad" transmission network use of system (TNUoS) charges which are levied only on consumption of each site, at the three half-hours of peak national demand. It is not known in advance when the three half-hours of peak national demand (the "triad" periods) will be, so the customer must run his diesels for a good deal more half-hours a year than just three.

The total capacity of reliably operable standby generation in Britain is estimated to be around 20 GW, nearly all of which is driven by diesel engines. This is equivalent to nearly 29% of the British system peak, although only a very small fraction will ever be generating at the same time. The most plant is for large office blocks, hospitals, supermarkets, and various installations where continuous power is important such as airports. Therefore, most are in urban areas, particularly city and commercial centers. It is estimated that around 10% of the plant exceeds 1 MW, about 50% is in the 200 kW-1 MW range, and the remaining 40% is sub-200 kW. Although it is growing, only a very small proportion is believed to be used regularly for peak lopping, the vast majority just being only for standby generation. The information in this paragraph is sourced from section 6.9 of the government report : "Overcoming Barriers To Scheduling Embedded Generation To Support Distribution Networks".

Increasing use of banks of diesel generators (known as "diesel farms") is being made in Britain to balance the fluctuating output from renewable energy sources, such as wind farms.

A similar system to Great Britain's Short Term Operating Reserve operates in France. It is known as EJP; at times of grid stress, special tariffs can mobilize at least 5 GW of diesel generating sets to become available. In this case, the diesels prime function is to feed power into the grid.

During normal operation in synchronization with the electricity net, powerplants are governed with a five percent droop speed control. This means the full load speed is 100% and the no load-speed is 105%. This is required for the stable operation of the net without hunting and dropouts of power plants. Normally the speed changes are minor. Adjustments in power output are made by slowly raising the droop curve by increasing the spring pressure on a centrifugal governor. Generally, this is a basic system requirement for all powerplants because the older and newer plants have to be compatible in response to the instantaneous changes in frequency without depending on outside communication.

Cost of generating electricity

Typical operating costs

Fuel consumption is the major portion of diesel plant owning and operating cost for power applications, whereas capital cost is the primary concern for backup generators. Specific consumption varies, but a modern diesel plant will, at its near-optimal 65-70% loading, generate at least 3 kWh per litre (ca. 30% fuel efficiency ratio).

Generator sizing and rating

Rating

Generators must provide the anticipated power required reliably and without damage and this is achieved by the manufacturer giving one or more ratings to a specific generator set model. A specific model of a generator operated as a standby generator may only need to operate for a few hours per year, but the same model operated as a prime power generator must operate continuously. When running, the standby generator may be operated with a specified - e.g. 10% overload that can be tolerated for the expected short running time. The same model generator will carry a higher rating for standby service than it will for continuous duty. Manufacturers give each set a rating based on internationally agreed definitions.

These standard rating definitions are designed to allow valid comparisons among manufacturers, prevent manufacturers from misrating their machines, and guide designers.

Generator Rating Definitions

Standby Rating based on Applicable for supplying emergency power for the duration of normal power interruption. No sustained overload capability is available for this rating. (Equivalent to Fuel Stop Power in accordance with ISO3046, AS2789, DIN6271 and BS5514). Nominally rated.

Typical application - emergency power plant in hospitals, offices, factories etc. Not connected to grid.

Prime (Unlimited Running Time) Rating: Should not be used for Construction Power applications. Output available with varying load for an unlimited time. Typical peak demand 100% of prime-rated ekW with 10% of overload capability for emergency use for a maximum of 1 hour in 12. A 10% overload capability is available for limited time. (Equivalent to Prime Power in accordance with ISO8528 and Overload Power in accordance with ISO3046, AS2789, DIN6271, and BS5514). This rating is not applicable to all generator set models.

Typical application - where the generator is the sole source of power for say a remote mining or construction site, fairground, festival etc.

Base Load (Continuous) Rating based on: Applicable for supplying power continuously to a constant load up to the full output rating for unlimited hours. No sustained overload capability is available for this rating. Consult an authorized distributor for rating. (Equivalent to Continuous Power in accordance with ISO8528, ISO3046, AS2789, DIN6271, and BS5514). This rating does not apply to all generator set models

Typical application - a generator running a continuous unvarying load, or paralleled with the mains and continuously feeding power at the maximum permissible level of 8,760 hours per year. This also applies to sets used for peak shaving /grid support even though this may only occur for say 200 hours per year.

As an example if in a particular set the Standby Rating was 1000 kW, then a Prime Power rating might be 850 kW, and the Continuous Rating 800 kW. However these ratings vary according to the manufacturer and should be taken from the manufacturer's datasheet.

Often a set might be given all three ratings stamped on the data plate, but sometimes it may have only a standby rating or only a prime rating.

Sizing

Typically however it is the size of the maximum load that has to be connected and the acceptable maximum voltage drop which determines the set size, not the ratings themselves. If the set is required to start motors, then the set will have to be at least three times the largest motor, which is normally started first. This means it will be unlikely to operate anywhere near the ratings of the chosen set.

Many gen-set manufacturers have software programs that enable the correct choice of a set for any given load combination. Sizing is based on site conditions and the type of appliances, equipment, and devices that will be powered by the generator set.

Fuels

Diesel fuel is named after diesel engines, and not vice versa; diesel engines are simply compression-ignition engines, and can operate on a variety of different fuels, depending on configuration and location. Where a gas grid connection is available, gas is often used, as the gas grid will remain pressurised during almost all power cuts. This is implemented by introducing gas with the intake air and using a small amount of diesel fuel for ignition. Conversion to 100% diesel fuel operation can be achieved instantaneously.

In more rural situations, or for low load factor plants, diesel fuel derived from crude oil is a common fuel; it is less likely to freeze than heavier oils. Endurance will be limited by tank size. Diesel engines can work with the full spectrum of crude oil distillates, from natural gas, alcohols, gasoline, and wood gas to fuel oils from diesel oil to cheaper residual fuels that are like lard at room temperature, and must be heated to enable them to flow down a fuel line.

Larger engines (from about 3 MWe to 30 MWe) sometimes use heavy oils, essentially tars, derived from the end of the refining process. The slight added complexity of keeping the fuel oil heated to enable it to flow, whilst mitigating the fire risks that come from over-heating fuel, makes these fuels unpopular for smaller, often unmanned, generating stations.

Other possible fuels include: biodiesel, straight vegetable oil, animal fats and tallows, glycerine, and coal-water slurry. These should be used with caution: because of their composition, the engine must be properly adjusted or they have a detrimental effect on engine life. For example, engines using coal-water slurry are often modified with larger injectors to permit the higher density fuel to be injected in the short fraction of a second time needed. Other high viscosity fuels like tallow, vegetable oil or paraffin wax can be used with standard fuel injectors if the fuel is preheated to reduce its viscosity to the range of standard ciesel fuel. The engine designed by and built by Rudolf Diesel for the 1900 World's Fair was fueled with peanut oil rather than a petroleum product like most modern engines using his system.

Spontaneous human combustion

From Wikipedia, the free encyclopedia

Spontaneous human combustion (SHC) is the pseudoscientific concept of the spontaneous combustion of a living (or recently deceased) human body without an apparent external source of ignition. In addition to reported cases, descriptions of the alleged phenomenon appear in literature, and both types have been observed to share common characteristics in terms of circumstances and the remains of the victim.

Scientific investigations have attempted to analyze reported instances of SHC and have resulted in hypotheses regarding potential causes and mechanisms, including victim behavior and habits, alcohol consumption, and proximity to potential sources of ignition, as well as the behavior of fires that consume melted fats. Natural explanations, as well as unverified natural phenomena, have been proposed to explain reports of SHC. Current scientific consensus is that purported cases of SHC involve overlooked external sources of ignition.

Overview

"Spontaneous human combustion" refers to the death from a fire originating without an apparent external source of ignition; a belief that the fire starts within the body of the victim. This idea and the term "spontaneous human combustion" were both first proposed in 1746 by Paul Rolli, a Fellow of the Royal Society, in an article published in the Philosophical Transactions concerning the mysterious death of Countess Cornelia Zangheri Bandi. Writing in The British Medical Journal in 1938, coroner Gavin Thurston describes the phenomenon as having "apparently attracted the attention not only of the medical profession but of the laity one hundred years ago" (referring to a fictional account published in 1834 in the Frederick Marryat cycle). In his 1995 book Ablaze!, Larry E. Arnold, a director of ParaScience International, wrote that there had been about 200 cited reports of spontaneous human combustion worldwide over a period of around 300 years.

Characteristics

The topic received coverage in the British Medical Journal in 1938. An article by L. A. Parry cited an 1823-published book Medical Jurisprudence, which stated that commonalities among recorded cases of spontaneous human combustion included the following characteristics:

  1. the victims are chronic alcoholics;
  2. they are usually elderly females;
  3. the body has not burned spontaneously, but some lighted substance has come into contact with it;
  4. the hands and feet usually fall off;
  5. the fire has caused very little damage to combustible things in contact with the body;
  6. the combustion of the body has left a residue of greasy and fetid ashes, very offensive in odour

Alcoholism is a common theme in early SHC literary references, in part because some Victorian era physicians and writers believed spontaneous human combustion was the result of alcoholism.

Scientific investigation

An extensive two-year research project, involving thirty historical cases of alleged SHC, was conducted in 1984 by science investigator Joe Nickell and forensic analyst John F. Fischer. Their lengthy, two-part report was published in the journal of the International Association of Arson Investigators, as well as part of a book. Nickell has written frequently on the subject, appeared on television documentaries, conducted additional research, and lectured at the New York State Academy of Fire Science at Montour Falls, New York, as a guest instructor.

Nickell and Fischer's investigation, which looked at cases in the 18th, 19th and 20th centuries, showed that the burned bodies were close to plausible sources for the ignition: candles, lamps, fireplaces, and so on. Such sources were often omitted from published accounts of these incidents, presumably to deepen the aura of mystery surrounding an apparently "spontaneous" death. The investigations also found that there was a correlation between alleged SHC deaths and the victim's intoxication (or other forms of incapacitation) which could conceivably have caused them to be careless and unable to respond properly to an accident. Where the destruction of the body was not particularly extensive, a primary source of combustible fuel could plausibly have been the victim's clothing or a covering such as a blanket or comforter.

However, where the destruction was extensive, additional fuel sources were involved, such as chair stuffing, floor coverings, the flooring itself, and the like. The investigators described how such materials helped to retain melted fat, which caused more of the body to be burned and destroyed, yielding still more liquified fat, in a cyclic process known as the "wick effect" or the "candle effect".

According to Nickell and Fischer's investigation, nearby objects often remained undamaged because fire tends to burn upward, but burns laterally with some difficulty. The fires in question are relatively small, achieving considerable destruction by the wick effect, and relatively nearby objects may not be close enough to catch fire themselves (much as one can closely approach a modest campfire without burning). As with other mysteries, Nickell and Fischer cautioned against "single, simplistic explanation for all unusual burning deaths" but rather urged investigating "on an individual basis".

Neurologist Steven Novella has said that skepticism about spontaneous human combustion is now bleeding over into becoming popular skepticism about spontaneous combustion.

A 2002 study by Angi M. Christensen of the University of Tennessee cremated both healthy and osteoporotic samples of human bone and compared the resulting color changes and fragmentation. The study found that osteoporotic bone samples "consistently displayed more discoloration and a greater degree of fragmentation than healthy ones." The same study found that when human tissue is burned, the resulting flame produces a small amount of heat, indicating that fire is unlikely to spread from burning tissue.

Suggested explanations

The scientific consensus is that incidents which might appear as spontaneous combustion did in fact have an external source of ignition, and that spontaneous human combustion without an external ignition source is extremely implausible. Pseudoscientific hypotheses have been presented which attempt to explain how SHC might occur without an external flame source. Benjamin Radford, science writer and deputy editor of the science magazine Skeptical Inquirer, casts doubt on the plausibility of spontaneous human combustion: "If SHC is a real phenomenon (and not the result of an elderly or infirm person being too close to a flame source), why doesn't it happen more often? There are 5 billion people in the world [ ⁠today in 2011⁠], and yet we don't see reports of people bursting into flame while walking down the street, attending football games, or sipping a coffee at a local Starbucks."

Natural explanations

  • Almost all postulated cases of SHC involve people with low mobility due to advanced age or obesity, along with poor health. Victims show a high likelihood of having died in their sleep, or of having been unable to move once they had caught fire.
  • Smoking is often seen as the source of fire. Natural causes such as heart attacks may lead to the victim dying, subsequently dropping the cigarette, which after a period of smouldering can ignite the victim's clothes.
  • The "wick effect" hypothesis suggests that a small external flame source, such as a burning cigarette, chars the clothing of the victim at a location, splitting the skin and releasing subcutaneous fat, which is in turn absorbed into the burned clothing, acting as a wick. This combustion can continue for as long as the fuel is available. This hypothesis has been successfully tested with pig tissue and is consistent with evidence recovered from cases of human combustion. The human body typically has enough stored energy in fat and other chemical stores to fully combust the body; even lean people have several pounds of fat in their tissues. This fat, once heated by the burning clothing, wicks into the clothing much as candle wax is drawn into a lit candle wick, providing the fuel needed to keep the wick burning. The protein in the body also burns, but provides less energy than fat, with the water in the body being the main impediment to combustion. However, slow combustion, lasting hours, gives the water time to evaporate slowly. In an enclosed area, such as a house, this moisture will recondense nearby, possibly on windows. Feet don't typically burn because they often have the least fat; hands also have little fat, but may burn if resting on the abdomen, which provides all of the necessary fat for combustion.
  • Scalding can cause burn-like injuries, sometimes leading to death, without setting fire to clothing. Although not applicable in cases where the body is charred and burnt, this has been suggested as a cause in at least one claimed SHC-like event.
  • Brian J. Ford has suggested that ketosis, possibly caused by alcoholism or low-carb dieting, produces acetone, which is highly flammable and could therefore lead to apparently spontaneous combustion.
  • SHC can be confused with self-immolation as a form of suicide. In the West, self-immolation accounts for 1% of suicides, while Radford claims in developing countries the figure can be as high as 40%.
  • Sometimes there are reasonable explanations for the deaths, but proponents ignore official autopsies and contradictory evidence in favor of anecdotal accounts and personal testimonies.
  • Inhaling/digesting phosphorus in different forms can cause the forming of phosphine which can autoignite

Alternative theories

  • Larry E. Arnold in his 1995 book Ablaze! proposed a pseudoscientific new subatomic particle, which he called "pyrotron". Arnold also wrote that the flammability of a human body could be increased by certain circumstances, like increased alcohol in the blood. He further proposed that extreme stress could be the trigger that starts many combustions. This process may use no external oxygen to spread throughout the body, since it may not be an "oxidation-reduction" reaction; however, no reaction mechanism has been proposed. Researcher Joe Nickell has criticised Arnold's hypotheses as based on selective evidence and argument from ignorance.
  • In his 1976 book Fire from Heaven, UK writer Michael Harrison suggests that SHC is connected to poltergeist activity because, he argues, "the force which activates the 'poltergeist' originates in, and is supplied by, a human being". Within the concluding summary, Harrison writes: "SHC, fatal or non-fatal, belongs to the extensive range of poltergeist phenomena."
  • John Abrahamson suggested that ball lightning could account for spontaneous human combustion. "This is circumstantial only, but the charring of human limbs seen in a number of ball lightning cases are [sic] very suggestive that this mechanism may also have occurred where people have had limbs combusted," says Abrahamson.

Notable examples

On 2 July 1951, Mary Reeser, a 67-year-old woman, was found burned to death in her house after her landlady realised that the house's doorknob was unusually warm. The landlady notified the police, and upon entering the home they found Reeser's remains completely burned into ash, with only one leg remaining. The chair she was sitting in was also destroyed. Reeser took sleeping pills and was also a smoker. Despite its proliferation in popular culture, the contemporary FBI investigation ruled out the possibility of SHC. A common theory was that she was smoking a cigarette after taking sleeping pills and then fell asleep while still holding the burning cigarette, which could have ignited her gown, ultimately leading to her death. Her daughter-in-law stated, "The cigarette dropped to her lap. Her fat was the fuel that kept her burning. The floor was cement, and the chair was by itself. There was nothing around her to burn".

Margaret Hogan, an 89-year-old widow who lived alone in a house on Prussia Street, Dublin, Ireland, was found burned almost to the point of complete destruction on 28 March 1970. Plastic flowers on a table in the centre of the room had been reduced to liquid and a television with a melted screen sat 12 feet from the armchair in which the ashen remains were found; otherwise, the surroundings were almost untouched. Her two feet, and both legs from below the knees, were undamaged. A small coal fire had been burning in the grate when a neighbour left the house the previous day; however, no connection between this fire and that in which Mrs. Hogan died could be found. An inquest, held on 3 April 1970, recorded death by burning, with the cause of the fire listed as "unknown".

Henry Thomas, a 73-year-old man, was found burned to death in the living room of his council house on the Rassau estate in Ebbw Vale, South Wales, in 1980. His entire body was incinerated, leaving only his skull and a portion of each leg below the knee. The feet and legs were still clothed in socks and trousers. Half of the chair in which he had been sitting was also destroyed. Police forensic officers decided that the incineration of Thomas was due to the wick effect.

In December 2010, the death of Michael Faherty, a 76-year-old man in County Galway, Ireland, was recorded as "spontaneous combustion" by the coroner. The doctor, Ciaran McLoughlin, made this statement at the inquiry into the death: "This fire was thoroughly investigated and I'm left with the conclusion that this fits into the category of spontaneous human combustion, for which there is no adequate explanation."

In this example from The Skeptic magazine, there were two children from the same family who were tragically burned to death in different places at the same time. The evidence showed that although the coincidence seemed strange, the children both loved to play with fire and had been "whipped" for this behavior in the past. Looking at all the evidence, the coroner and jury ruled that these were both accidental deaths.

In popular culture

  • In the novel Redburn by Herman Melville published in 1849, a sailor, Miguel Saveda, is consumed by "animal combustion" while in a drunken stupor on the return voyage from Liverpool to New York.
  • In the novel Bleak House by Charles Dickens, the character Mr. Krook dies of spontaneous combustion at the end of Part X. Dickens researched the details of a number of contemporary accounts of spontaneous human combustion before writing that part of the novel and, after receiving criticism from a scientist friend suggesting he was perpetuating a "vulgar error", cites some of these cases in Part XI and again in the preface to the one-volume edition. The death of Mr. Krook has been described as "the most famous case in literature" of spontaneous human combustion.
  • In the comic story "The Glenmutchkin Railway" by William Edmondstoune Aytoun, published in 1845 in Blackwood's Magazine, one of the railway directors, Sir Polloxfen Tremens, is said to have died of spontaneous combustion.
  • In the 1984 mockumentary This Is Spın̈al Tap, about the fictional heavy metal band Spinal Tap, two of the band's former drummers are said to have died in separate on-stage spontaneous human combustion incidents.
  • In the episode "Confidence and Paranoia" of British science fiction series Red Dwarf, a character called the Mayor of Warsaw is said to have spontaneously exploded in the 16th century and briefly appears in a vision by an unconscious Lister (the main protagonist of the series) where he explodes in front of Rimmer (his hologram bunkmate).
  • In the beginning of the 1998 video game Parasite Eve, an entire audience in Carnegie Hall spontaneously combusts (except for Aya Brea, the protagonist of the game) during an opera presentation as the main actress Melissa Pierce starts to sing.
  • This phenomenon is mentioned in the TV series The X-Files.
  • Bob Shaw’s 1984 sci-fi book, Fire Pattern, is about a reporter who investigates people who spontaneously combust, and discovers a startling conspiracy behind the phenomenon.
  • In the episode "Heart Break" of the second season of the American action police procedural television series NCIS, a case is investigated where the victim at first glance seems to have been killed by spontaneous human combustion.
  • In episode "Duty Free Rome" of the second season of the TV series Picket Fences, the town's mayor is shown to have been killed by spontaneous combustion.
  • In the seventh season episode “Mars Attacks” of the American TV medical drama ER, a patient is treated for “spontaneous human combustion” and subsequently catches fire.
  • The manga and anime series Fire Force (En'en no Shōbōtai) focuses on the main protagonists fighting humans who have this phenomenon.
  • In the fourth episode of the first season of the English comedic drama series "Toast of London", Toast decides to finish his book by having the main character spontaneously combust. When bringing it to his literary agent, the laziness of his ending enrages her to the point of spontaneous combustion in front of Toast.
  • The adult animated series South Park devoted a whole episode, titled "Spontaneous Combustion", to spontaneous human combustion.
  • In Kevin Wilson's short story "Blowing Up on the Spot" (from his collection Tunneling to the Center of the Earth), the protagonist's parents died from a "double spontaneous human combustion."
  • In the 2020 American black comedy horror film Spontaneous, high school students at Covington High begin to inexplicably explode.
  • In episode 12 of Now and Again, Michael investigates a church that uses spontaneous human combustion.

Wi-Fi hotspot

From Wikipedia, the free encyclopedia
A diagram showing a Wi-Fi network

A hotspot is a physical location where people can obtain Internet access, typically using Wi-Fi technology, via a wireless local-area network (WLAN) using a router connected to an Internet service provider.

Public hotspots may be created by a business for use by customers, such as coffee shops or hotels. Public hotspots are typically created from wireless access points configured to provide Internet access, controlled to some degree by the venue. In its simplest form, venues that have broadband Internet access can create public wireless access by configuring an access point (AP), in conjunction with a router to connect the AP to the Internet. A single wireless router combining these functions may suffice.

A private hotspot, often called tethering, may be configured on a smartphone or tablet that has a network data plan, to allow Internet access to other devices via Bluetooth pairing, or through the RNDIS protocol over USB, or even when both the hotspot device and the device[s] accessing it are connected to the same Wi-Fi network but one which does not provide Internet access. Similarly, a Bluetooth or USB OTG can be used by a mobile device to provide Internet access via Wi-Fi instead of a mobile network, to a device that itself has neither Wi-Fi nor mobile network capability.

Uses

The public can use a laptop or other suitable portable device to access the wireless connection (usually Wi-Fi) provided. Of the estimated 150 million laptops, 14 million PDAs, and other emerging Wi-Fi devices sold per year for the last few years, most include the Wi-Fi feature.

The iPass 2014 interactive map, that shows data provided by the analysts Maravedis Rethink, shows that in December 2014 there are 46,000,000 hotspots worldwide and more than 22,000,000 roamable hotspots. More than 10,900 hotspots are on trains, planes and airports (Wi-Fi in motion) and more than 8,500,000 are "branded" hotspots (retail, cafés, hotels). The region with the largest number of public hotspots is Europe, followed by North America and Asia.

Libraries throughout the United States are implementing hotspot lending programs to extend access to online library services to users at home who cannot afford in-home Internet access or do not have access to Internet infrastructure. The New York Public Library was the largest program, lending out 10,000 devices to library patrons. Similar programs have existed in Kansas, Maine, and Oklahoma; and many individual libraries are implementing these programs.

Wi-Fi positioning is a method for geolocation based on the positions of nearby hotspots.

Security issues

Security is a serious concern in connection with public and private hotspots. There are three possible attack scenarios. First, there is the wireless connection between the client and the access point, which needs to be encrypted, so that the connection cannot be eavesdropped or attacked by a man-in-the-middle attack. Second, there is the hotspot itself. The WLAN encryption ends at the interface, then travels its network stack unencrypted and then, third, travels over the wired connection up to the BRAS of the ISP.

Depending upon the setup of a public hotspot, the provider of the hotspot has access to the metadata and content accessed by users of the hotspot. The safest method when accessing the Internet over a hotspot, with unknown security measures, is end-to-end encryption. Examples of strong end-to-end encryption are HTTPS and SSH.

Some hotspots authenticate users; however, this does not prevent users from viewing network traffic using packet sniffers.

Some vendors provide a download option that deploys WPA support. This conflicts with enterprise configurations that have solutions specific to their internal WLAN.

The Opportunistic Wireless Encryption (OWE) standard provides encrypted communication in open Wi-Fi networks, alongside the WPA3 standard, but is not yet widely implemented.

Unintended consequences

New York City introduced a Wi-Fi hotspot kiosk called LinkNYC with the intentions of providing modern technology for the masses as a replacement to a payphone. Businesses complained they were a homeless magnet and CBS news observed transients with wires connected to the kiosk lingering for an extended period. It was shut down following complaints about transient activity around the station and encampments forming around it. Transients/panhandlers were the most frequent users of the kiosk since its installation in early 2016 spurring complaints about public viewing of pornography and masturbation.

Locations

Public hotspots are often found at airports, bookstores, coffee shops, department stores, fuel stations, hotels, hospitals, libraries, public pay phones, restaurants, RV parks and campgrounds, supermarkets, train stations, and other public places. Additionally, many schools and universities have wireless networks on their campuses.

Types

Free hotspots

public Wi-Fi hotspot in Zurich

According to statista.com, in the year 2022, there are approximately 550 million free Wi-Fi hotspots around the world. The U.S. NSA warns against connecting to free public Wi-Fi.

Free hotspots operate in two ways:

  • Using an open public network is the easiest way to create a free hotspot. All that is needed is a Wi-Fi router. Similarly, when users of private wireless routers turn off their authentication requirements, opening their connection, intentionally or not, they permit piggybacking (sharing) by anyone in range.
  • Closed public networks use a HotSpot Management System to control access to hotspots. This software runs on the router itself or an external computer allowing operators to authorize only specific users to access the Internet. Providers of such hotspots often associate the free access with a menu, membership, or purchase limit. Operators may also limit each user's available bandwidth (upload and download speed) to ensure that everyone gets a good quality service. Often this is done through service-level agreements.

Commercial hotspots

A commercial hotspot may feature:

Many services provide payment services to hotspot providers, for a monthly fee or commission from the end-user income. For example, Amazingports can be used to set up hotspots that intend to offer both fee-based and free internet access, and ZoneCD is a Linux distribution that provides payment services for hotspot providers who wish to deploy their own service.

Roaming services are expanding among major hotspot service providers. With roaming service the users of a commercial provider can have access to other providers' hotspots, either free of charge or for extra fees, which users will usually be charged on an access-per-minute basis.

Software hotspots

Many Wi-Fi adapters built into or easily added to consumer computers and mobile devices include the functionality to operate as private or mobile hotspots, sometimes referred to as "mi-fi". The use of a private hotspot to enable other personal devices to access the WAN (usually but not always the Internet) is a form of bridging, and known as tethering. Manufacturers and firmware creators can enable this functionality in Wi-Fi devices on many Wi-Fi devices, depending upon the capabilities of the hardware, and most modern consumer operating systems, including Android, Apple OS X 10.6 and later, Windows, and Linux include features to support this. Additionally wireless chipset manufacturers such as Atheros, Broadcom, Intel and others, may add the capability for certain Wi-Fi NICs, usually used in a client role, to also be used for hotspot purposes. However, some service providers, such as AT&T, Sprint, and T-Mobile charge users for this service or prohibit and disconnect user connections if tethering is detected.

Third-party software vendors offer applications to allow users to operate their own hotspot, whether to access the Internet when on the go, share an existing connection, or extend the range of another hotspot.

Hotspot 2.0

Hotspot 2.0, also known as HS2 and Wi-Fi Certified Passpoint, is an approach to public access Wi-Fi by the Wi-Fi Alliance. The idea is for mobile devices to automatically join a Wi-Fi subscriber service whenever the user enters a Hotspot 2.0 area, in order to provide better bandwidth and services-on-demand to end-users and relieve carrier infrastructure of some traffic.

Hotspot 2.0 is based on the IEEE 802.11u standard, which is a set of protocols published in 2011 to enable cellular-like roaming. If the device supports 802.11u and is subscribed to a Hotspot 2.0 service it will automatically connect and roam.

Supported devices

  • Apple mobile devices running iOS 7 and up
  • Some Samsung Galaxy smartphones
  • Windows 10 devices have full support for network discovery and connection.
  • Windows 8 and Windows 8.1 lack network discovery, but support connecting to a network when the credentials are known.

Billing

EDCF user-priority list
  Net traffic
low high
Audio Video Data Audio Video Data
User needs time-critical 7 5 0 6 4 0
not time-critical - - 2 - - 2

The "user-fairness model" is a dynamic billing model, which allows volume-based billing, charged only by the amount of payload (data, video, audio). Moreover, the tariff is classified by net traffic and user needs.

If the net traffic increases, then the user has to pay the next higher tariff class. The user can be prompted to confirm that they want to continue the session in the higher traffic class. A higher class fare can also be charged for delay sensitive applications such as video and audio, versus non time-critical applications such as reading Web pages and sending e-mail.

Tariff classes of the user-fairness model
  Net traffic
low high
User needs time-critical standard exclusive
not time-critical low priced standard

The "User-fairness model" can be implemented with the help of EDCF (IEEE 802.11e). An EDCF user priority list shares the traffic in 3 access categories (data, video, audio) and user priorities (UP).

  • Data [UP 0|2]
  • Video [UP 5|4]
  • Audio [UP 7|6]

See Service-oriented provisioning for viable implementations.

Legal issues

Depending upon the set up of a public hotspot, the provider of the hotspot has access to the metadata and content accessed by users of the hotspot, and may have legal obligations related to privacy requirements and liability for use of the hotspot for unlawful purposes. In countries where the internet is regulated or freedom of speech more restricted, there may be requirements such as licensing, logging, or recording of user information. Concerns may also relate to child safety, and social issues such as exposure to objectionable content, protection against cyberbullying and illegal behaviours, and prevention of perpetration of such behaviors by hotspot users themselves.

European Union

The Data Retention Directive which required hotspot owners to retain key user statistics for 12 months was annulled by the Court of Justice of the European Union in 2014. The Directive on Privacy and Electronic Communications was replaced in 2018 by the General Data Protection Regulation, which imposes restrictions on data collection by hotspot operators.

United Kingdom

History

Public park in Brooklyn, New York has free Wi-Fi from a local corporation.

Public access wireless local area networks (LANs) were first proposed by Henrik Sjoden at the NetWorld+Interop conference in The Moscone Center in San Francisco in August 1993. Sjoden did not use the term "hotspot" but referred to publicly accessible wireless LANs.

The first commercial venture to attempt to create a public local area access network was a firm founded in Richardson, Texas known as PLANCOM (Public Local Area Network Communications). The founders of the venture, Mark Goode, Greg Jackson, and Brett Stewart dissolved the firm in 1998, while Goode and Jackson created MobileStar Networks. The firm was one of the first to sign such public access locations as Starbucks, American Airlines, and Hilton Hotels. The company was sold to Deutsche Telecom in 2001, who then converted the name of the firm into "T-Mobile Hotspot". It was then that the term "hotspot" entered the popular vernacular as a reference to a location where a publicly accessible wireless LAN is available.

ABI Research reported there was a total of 4.9 million global Wi-Fi hotspots in 2012. In 2016 the Wireless Broadband Alliance predicted a steady annual increase from 5.2m public hotspots in 2012 to 10.5m in 2018.

Bayesian inference

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Bayesian_inference Bayesian inference ( / ...