War of Currents

War of Currents

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In the "War of Currents" era (sometimes, "War of the Currents" or "Battle of Currents") in the late 1880s, George Westinghouse
George Westinghouse
George Westinghouse, Jr was an American entrepreneur and engineer who invented the railway air brake and was a pioneer of the electrical industry. Westinghouse was one of Thomas Edison's main rivals in the early implementation of the American electricity system...

 and Thomas Edison
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...

 became adversaries due to Edison's promotion of direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 (DC) for electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

 distribution over alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 (AC) advocated by several European companies and Westinghouse Electric based out of Pittsburgh, PA.

Background


During the initial years of electricity distribution
Electricity distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...

, Edison's direct current was the standard for the United States and Edison did not want to lose all his patent royalties. Direct current worked well with incandescent lamps that were the principal load of the day, and with motors. 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. At the introduction of Edison's system, no practical AC motor was available. Edison had invented a meter to allow customers to be billed for energy proportional to consumption, but this meter worked only with direct current. As of 1882 these were all significant technical advantages of direct current.

Alternating current had first developed in Europe due to the work of Guillaume Duchenne (1850s), Ganz Company (1870s), Sebastian Ziani de Ferranti
Sebastian Ziani de Ferranti
Sebastian Pietro Innocenzo Adhemar Ziani de Ferranti was an electrical engineer and inventor.-Personal life:...

 (1880s), Lucien Gaulard
Lucien Gaulard
Lucien Gaulard invented devices for the transmission of alternating current electrical energy.-Biography:Gaulard was born in Paris, France....

, and Galileo Ferraris
Galileo Ferraris
Galileo Ferraris was an Italian physicist and electrical engineer, noted mostly for the studies and independent discovery of the rotating magnetic field, a basic working principle of the induction motor...

. In North America one of the believers in the new technology was George Westinghouse. Westinghouse was willing to invest in the technology and hired William Stanley, Jr.
William Stanley, Jr.
William Stanley, Jr. was an American physicist born in Brooklyn, New York. In his career, he obtained 129 patents covering a variety of electric devices.-Biography:...

 to work on an AC distribution system using step up and step down transformers of a new design in 1886. After Stanley left Westinghouse, Oliver Shallenberger took control of the AC project. Nikola Tesla
Nikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...

 joined the team after 1888. Tesla partnered with Westinghouse Electric to commercialize his particular AC system. Westinghouse had previously bought the rights to Tesla's polyphase system
Polyphase system
A polyphase system is a means of distributing alternating current electrical power. Polyphase systems have three or more energized electrical conductors carrying alternating currents with a definite time offset between the voltage waves in each conductor. Polyphase systems are particularly useful...

 patents and other patents for AC transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

s from Lucien Gaulard
Lucien Gaulard
Lucien Gaulard invented devices for the transmission of alternating current electrical energy.-Biography:Gaulard was born in Paris, France....

 and John Dixon Gibbs.

Several undercurrents lay beneath this rivalry. Edison did not have the mathematical background that many new engineering graduates had at the time. C.S. Bradley and Tesla were just two examples of young men who believed in AC, had worked for Edison, and had left Edison due to their belief. AC cannot be properly understood or exploited without a substantial understanding of mathematics and mathematical physics (see AC power
AC power
Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow...

). In addition to the business rivalry of companies like Oerlikon, Siemens, Westinghouse (all AC promotors) and the powerful Edison Electric, a personal rivalry developed between Nikola Tesla and Thomas A. Edison due to certain events: Tesla had worked for Edison but felt he was undervalued (for example, when Edison first learned of the idea of alternating-current power transmission, he dismissed it: "[Tesla's] ideas are splendid, but they are utterly impractical."). Bad feelings were exacerbated because Tesla had been cheated by Edison of promised compensation for his work. Edison later came to regret that he had not listened to Tesla and used alternating current. The "War of Currents" is often personified by the Tesla vs. Edison personal rivalry, however the "War of Currents" was much larger than that, it involved companies on both sides of the Atlantic which had invested heavily in AC or DC, each company hoped they would dominate the industry.

The competing systems


Edison's DC distribution system consisted of generating plants feeding heavy distribution conductors, with customer loads (lighting and motors) tapped off them. The system operated at the same voltage level throughout; for example, 100 volt lamps at the customer's location would be connected to a generator supplying 110 volts, to allow for some voltage drop in the wires between the generator and load. The voltage level was chosen for convenience in lamp manufacture; high-resistance carbon filament lamps could be constructed to withstand 100 volts, and to provide lighting performance economically competitive with gas lighting. At the time it was felt that 100 volts was not likely to present a severe hazard of fatal electric shock
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....

.

To save on the cost of copper conductors, a three-wire
Split phase
A split-phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial applications. It is the AC equivalent of the original Edison 3-wire direct current system...

 distribution system was used. The three wires were at +110 volts, 0 volts and −110 volts relative potential. 100-volt lamps could be operated between either the +110 or −110 volt legs of the system and the 0-volt "neutral"
Ground and neutral
Since the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding of equipment and structures...

 conductor, which carried only the unbalanced current between the + and − sources. The resulting three-wire system used less copper wire for a given quantity of electric power transmitted, while still maintaining (relatively) low voltages. However, even with this innovation, the voltage drop
Voltage drop
Voltage drop is the reduction in voltage in the passive elements of an electrical circuit. Voltage drops across conductors, contacts, connectors and source internal resistances are undesired as they reduce the supplied voltage while voltage drops across loads and other electrical and electronic...

 due to the resistance of the system conductors was so high that generating plants had to be located within a mile (1–2 km) or so of the load. Higher voltages could not so easily be used with the DC system because there was no efficient low-cost technology that would allow reduction of a high transmission voltage to a low utilization voltage.


In the alternating current system, a transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

 was used between the (relatively) high voltage distribution system and the customer loads. Lamps and small motors could still be operated at some convenient low voltage. However, the transformer would allow power to be transmitted at much higher voltages, say, ten times that of the loads. For a given quantity of power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

 transmitted, the wire cross-sectional area would be inversely proportional to the voltage used. Alternatively, the allowable length of a circuit, given a wire size and allowable voltage drop, would increase approximately as the square of the distribution voltage. This had the practical significance that fewer, larger generating plants could serve the load in a given area. Large loads, such as industrial motors or converters for electric railway power, could be served by the same distribution network that fed lighting, by using a transformer with a suitable secondary voltage.

Early transmission analysis


Edison's response to the limitations of direct current was to generate power close to where it was consumed (today called distributed generation
Distributed generation
Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources....

) and install large conductors to handle the growing demand for electricity, but this solution proved to be costly (especially for rural areas which could not afford to build a local station or to pay for massive amounts of very thick copper wire), impractical (including, but not limited to, inefficient voltage conversion) and unmanageable. Edison and his company, though, would have profited extensively from the construction of the multitude of power plants required to make electricity available in many areas.

Direct current could not easily be converted to higher or lower voltages. This meant that separate electrical lines had to be installed to supply power to appliances that used different voltages, for example, lighting and electric motors. This required more wires to lay and maintain, wasting money and introducing unnecessary hazards. A number of deaths in the Great Blizzard of 1888
Great Blizzard of 1888
The Great Blizzard of 1888 or Great Blizzard of '88 was one of the most severe blizzards in United States' recorded history. Snowfalls of 40-50 inches fell in parts of New Jersey, New York, Massachusetts and Connecticut, and sustained winds of over produced snowdrifts in excess of...

 were attributed to collapsing overhead power lines in New York City.

Alternating current could be transmitted over long distances at high voltages, using lower current, and thus lower energy loss and greater transmission efficiency, and then conveniently stepped down to low voltages for use in homes and factories. When Tesla introduced a system for alternating current generators, transformers, motors, wires and lights in November and December 1887, it became clear that AC was the future of electric power distribution
Electric power distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...

, although DC distribution was used in downtown metropolitan areas for decades thereafter.

Low-frequency (50–60 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

) alternating currents can be more dangerous than similar levels of DC since the alternating fluctuations can cause the heart to lose coordination, inducing ventricular fibrillation
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...

, a deadly heart rhythm that must be corrected immediately. However, any practical distribution system will use voltage levels quite sufficient for a dangerous amount of current to flow, whether it uses alternating or direct current. As precautions against electrocution are similar for both AC and DC, the technical and economic advantages of AC power transmission
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 outweighed this theoretical risk, and it was eventually adopted as the standard worldwide.


Transmission loss


The advantage of AC for distributing power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...

 over a distance is due to the ease of changing voltages using a transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

. Available power is the product of current × voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 at the load. For a given amount of power, a low voltage requires a higher current and a higher voltage requires a lower current. Since metal conducting wires have an almost fixed electrical resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

, some power will be wasted as heat in the wires. This power loss is given by Joule's laws and is proportional to the square of the current. Thus, if the overall transmitted power is the same, and given the constraints of practical conductor sizes, high-current, low-voltage transmissions will suffer a much greater power loss than low-current, high-voltage ones. This holds whether DC or AC is used.

Converting DC power from one voltage to another requires a large spinning rotary converter
Rotary converter
A rotary converter is a type of electrical machine which acts as a mechanical rectifier or inverter. It was used to convert AC to DC or DC to AC power before the advent of chemical or solid state power rectification...

 or motor-generator set, which was difficult, expensive, inefficient, and required maintenance, whereas with AC the voltage can be changed with simple and efficient transformers that have no moving parts and require very little maintenance. This was the key to the success of the AC system. Modern transmission grids regularly use AC voltages up to 765,000 volts. Power electronic devices such as the mercury arc valve
Mercury arc valve
A mercury-arc valve is a type of electrical rectifier used for converting high-voltage or high-current alternating current into direct current . Rectifiers of this type were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for...

 and thyristor
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...

 made high-voltage direct current
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...

 transmission practical by improving the reliability and efficiency of conversion between alternating and direct current.

Alternating-current transmission lines have losses that do not occur with direct current. Due to the skin effect
Skin effect
Skin effect is the tendency of an alternating electric current to distribute itself within a conductor with the current density being largest near the surface of the conductor, decreasing at greater depths. In other words, the electric current flows mainly at the "skin" of the conductor, at an...

, a conductor will have a higher resistance to alternating current than to direct current; the effect is measurable and of practical significance for large conductors carrying thousands of amperes. The increased resistance due to the skin effect can be offset by changing the shape of conductors from a solid core to a braid of many small (isolated) wires. However, total losses in systems using high-voltage transmission and transformers to reduce the voltage are very much lower than DC transmission at working voltage.

Edison's publicity campaign


Edison carried out a campaign to discourage the use
Fear, uncertainty and doubt
Fear, uncertainty and doubt, frequently abbreviated as FUD, is a tactic used in sales, marketing, public relations, politics and propaganda....

 of alternating current, including spreading disinformation on fatal AC accidents, publicly killing animals, and lobbying against the use of AC in state legislatures. Edison directed his technicians, primarily Arthur Kennelly and Harold P. Brown
Harold P. Brown
Harold Pitney Brown was the American credited with building the original electric chair based on the design by Dr. Alfred P. Southwick...

, to preside over several AC-driven killings of animals, primarily stray cats and dogs but also unwanted cattle and horses. Acting on these directives, they were to demonstrate to the press that alternating current was more dangerous than Edison's system of direct current. He also tried to popularize the term for being electrocuted as being "Westinghoused". Years after DC had lost the "war of the currents," in 1902, his film crew made a movie of the electrocution with high voltage AC, supervised by Edison employees, of Topsy, a Coney Island circus elephant which had recently killed three men.

Edison opposed capital punishment
Capital punishment
Capital punishment, the death penalty, or execution is the sentence of death upon a person by the state as a punishment for an offence. Crimes that can result in a death penalty are known as capital crimes or capital offences. The term capital originates from the Latin capitalis, literally...

, but his desire to disparage the system of alternating current led to the invention of the electric chair
Electric chair
Execution by electrocution, usually performed using an electric chair, is an execution method originating in the United States in which the condemned person is strapped to a specially built wooden chair and electrocuted through electrodes placed on the body...

. Harold P. Brown
Harold P. Brown
Harold Pitney Brown was the American credited with building the original electric chair based on the design by Dr. Alfred P. Southwick...

, who was being secretly paid by Edison, built the first electric chair for the state of New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

 to promote the idea that alternating current was deadlier than DC.

When the chair was first used, on August 6, 1890, the technicians on hand misjudged the voltage needed to kill the condemned prisoner, William Kemmler
William Kemmler
William Francis Kemmler of Buffalo, New York, was a convicted murderer and the first person in the world to be executed using an electric chair.-Early life:...

. The first jolt of electricity was not enough to kill Kemmler, and only left him badly injured. 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."

Niagara Falls


In 1889, the first AC hydroelectric
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 plant, Williamette Falls Station, began operation in Oregon City, Oregon. In 1890, the Niagara Falls Power Company (NFPC) and its subsidiary Cataract Company formed the International Niagara Commission composed of experts, to analyze proposals to harness Niagara Falls
Niagara Falls
The Niagara Falls, located on the Niagara River draining Lake Erie into Lake Ontario, is the collective name for the Horseshoe Falls and the adjacent American Falls along with the comparatively small Bridal Veil Falls, which combined form the highest flow rate of any waterfalls in the world and has...

 to generate electricity. The commission was led by Sir William Thomson (later Lord Kelvin) and included Eleuthère Mascart
Éleuthère Mascart
Éleuthère Élie Nicolas Mascart was a noted French physicist, a researcher in optics and electricity.Mascart was born in Quarouble, Nord. He attended the École normale supérieure...

 from France, William Unwin
William Unwin
William Cawthorne Unwin FRS was a British civil and mechanical engineer. He is noted for his extensive work on hydraulics and engines as well as his close association with William Fairbairn. He is one of only a few men who have served as president of both the Institution of Civil Engineers and the...

 from England, Coleman Sellers from the US, and Théodore Turrettini from Switzerland. It was backed by entrepreneur
Entrepreneur
An entrepreneur is an owner or manager of a business enterprise who makes money through risk and initiative.The term was originally a loanword from French and was first defined by the Irish-French economist Richard Cantillon. Entrepreneur in English is a term applied to a person who is willing to...

s such as J. P. Morgan
J. P. Morgan
John Pierpont Morgan was an American financier, banker and art collector who dominated corporate finance and industrial consolidation during his time. In 1892 Morgan arranged the merger of Edison General Electric and Thomson-Houston Electric Company to form General Electric...

, Lord Rothschild, and John Jacob Astor IV
John Jacob Astor IV
John Jacob Astor IV was an American businessman, real estate builder, investor, inventor, writer, lieutenant colonel in the Spanish-American War and a member of the prominent Astor family...

. Among 19 proposals, they even briefly considered compressed air
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

 as a power transmission
Power transmission
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.Power is defined formally as units of energy per unit time...

 medium, but preferred electricity. But they could not decide which method would be best overall.

In 1893, NFPC was finally convinced by George Forbes
George Forbes (scientist)
George Forbes FRS was an electrical engineer, astronomer, explorer, author and inventor, some of whose inventions are still in use.-Early life:...

 to award the contract to Westinghouse, and to reject General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

 and Edison's proposal. Work began in 1893 on the Niagara Falls generation project: power was to be generated and transmitted as alternating current, at a frequency of 25 Hz to minimize impedance losses in transmission (changed to 60 Hz in the 1950s).

Some doubted that the system would generate enough electricity to power industry in Buffalo
Buffalo, New York
Buffalo is the second most populous city in the state of New York, after New York City. Located in Western New York on the eastern shores of Lake Erie and at the head of the Niagara River across from Fort Erie, Ontario, Buffalo is the seat of Erie County and the principal city of the...

. Tesla was sure it would work, saying that Niagara Falls could power the entire eastern United States. None of the previous polyphase alternating current transmission demonstration projects were on the scale of power available from Niagara:
  • The Lauffen-Neckar demonstration
    International Electro-Technical Exhibition - 1891
    The 1891 International Electro-Technical Exhibition was held between 16 May and 19 October on the disused site of the three former “Westbahnhöfe” in Frankfurt am Main. The exhibition featured the first long distance transmission of high-power, three-phase electrical current, which was generated...

     in 1891
  • Westinghouse successfully used Tesla's AC system in the commercial Ames Hydroelectric Generating Plant
    Ames Hydroelectric Generating Plant
    The Ames Hydroelectric Generating Plant, located near Ophir, Colorado, was the world's first commercial system to produce and transmit alternating current electricity. It is now on the List of IEEE Milestones....

     in 1891
  • The Chicago World's Fair in 1893
    World's Columbian Exposition
    The World's Columbian Exposition was a World's Fair held in Chicago in 1893 to celebrate the 400th anniversary of Christopher Columbus's arrival in the New World in 1492. Chicago bested New York City; Washington, D.C.; and St...

     exhibited a complete polyphase generation and distribution system installed by Westinghouse
  • Almirian Decker designed a three-phase
    Three-phase
    In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are radians offset in time...

     AC system at Mill Creek California in 1893


On November 16, 1896, electrical power was transmitted to industries in Buffalo from the hydroelectric generators at the Edward Dean Adams Station at Niagara Falls. The generators were built by Westinghouse Electric Corporation using Tesla's AC system patent. The nameplates on the generators bore Tesla's name. To appease the interests of General Electric, they were awarded the contract to construct the transmission lines to Buffalo using the Tesla patents.

Competition outcome


The "end" of the "War of Currents" was marked in 1891 by the International Electro-Technical Exhibition – 1891 in Frankfurt Germany (Die Elektrotechnische Ausstellung). During this exposition a three phase AC power system developed by Mikhail Dolivo-Dobrovolsky and Oerlikon was able to send power over 109 miles from Lauffen to Frankfurt. It successfully operated motors and lights at the fair. Many corporate technical representatives (including E.W. Rice of Thomson-Houston Electric Company (what became General Electric)) attended. The technical advisors and representatives were impressed. The following year General Electric formed and immediately invested heavily in AC power (at this time Thomas Edison's opinions on company direction were muted by President Coffin and the GE board of directors). Westinghouse was already ahead in AC, but it only took a few years for General Electric to catch up, mainly thanks to Charles Proteus Steinmetz
Charles Proteus Steinmetz
Charles Proteus Steinmetz was a German-American mathematician and electrical engineer. He fostered the development of alternating current that made possible the expansion of the electric power industry in the United States, formulating mathematical theories for engineers...

, 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 apparatus. In Europe Siemens and Halske became the dominant force. Three phase 60 Hz at 120 volts became the dominant system in North America while 220-240 volts at 50 Hz became the standard in Europe.

Alternating current power transmission networks today provide redundant path
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....

s and lines for power routing from any power plant to any load center, based on the economics of the transmission path, the cost of power, and the importance of keeping a particular load center powered at all times. Generators (such as hydroelectric sites) can be located far from the loads.

Remnant and existent DC systems


Some cities continued to use DC well into the 20th century. For example, central Helsinki
Helsinki
Helsinki is the capital and largest city in Finland. It is in the region of Uusimaa, located in southern Finland, on the shore of the Gulf of Finland, an arm of the Baltic Sea. The population of the city of Helsinki is , making it by far the most populous municipality in Finland. Helsinki is...

 had a DC network until the late 1940s, and Stockholm lost its dwindling DC network as late as the 1970s. A mercury arc valve
Mercury arc valve
A mercury-arc valve is a type of electrical rectifier used for converting high-voltage or high-current alternating current into direct current . Rectifiers of this type were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for...

 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 many destroyed small appliances (typically hair dryers and phonographs) used by Boston University
Boston University
Boston University is a private research university located in Boston, Massachusetts. With more than 4,000 faculty members and more than 31,000 students, Boston University is one of the largest private universities in the United States and one of Boston's largest employers...

 students who ignored warnings about the electricity supply. New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

's electric utility company, Consolidated Edison
Consolidated Edison
Consolidated Edison, Inc. is one of the largest investor-owned energy companies in the United States, with approximately $14 billion in annual revenues and $36 billion in assets...

, continued to supply direct current to customers who had adopted it early in the twentieth century, mainly for elevators. The New Yorker Hotel
New Yorker Hotel
The New Yorker Hotel, is a hotel located 481 Eighth Avenue in New York City. The 43-story Art Deco hotel opened in 1930.-General:The New Yorker Hotel is a 900 room, mid-priced hotel. It is located in Manhattan's Garment Center, central to Pennsylvania Station, Madison Square Garden, Times Square...

, constructed in 1929, had a large direct-current power plant and did not convert fully to alternating-current service until well into the 1960s. Ironically, this was the same building in which AC pioneer Nikola Tesla spent his last years, and where he died in 1943. 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 rectifier
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...

s.

Other isolated uses remained, Alcatraz Island
Alcatraz Island
Alcatraz Island is an island located in the San Francisco Bay, offshore from San Francisco, California, United States. Often referred to as "The Rock" or simply "Traz", the small island was developed with facilities for a lighthouse, a military fortification, a military prison, and a Federal...

, as long as it was a prison up through 1963 generated its own DC power.

The Central Electricity Generating Board in the UK continued to maintain a 200 volt DC generating station at Bankside Power Station
Bankside Power Station
Bankside Power Station is a former oil-fired power station, located on the south bank of the River Thames, in the Bankside district of London. It generated electricity from 1952 to 1981. Since 2000 the station's building has been used to house the Tate Modern art museum.-History:The station was...

 on the River Thames
River Thames
The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 as late as 1981. It exclusively powered DC printing machinery in Fleet Street
Fleet Street
Fleet Street is a street in central London, United Kingdom, named after the River Fleet, a stream that now flows underground. It was the home of the British press until the 1980s...

, 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). The building was converted into an art gallery, the Tate Modern
Tate Modern
Tate Modern is a modern art gallery located in London, England. It is Britain's national gallery of international modern art and forms part of the Tate group . It is the most-visited modern art gallery in the world, with around 4.7 million visitors per year...

.

Electric railways that use a third-rail system generally employ DC power between 500 and 750 volts; railways with overhead catenary lines use a number of power schemes including both high-voltage AC and high-current DC.

High voltage direct current (HVDC) systems are used for bulk transmission of energy from distant generating stations or for interconnection of separate alternating-current systems. These HVDC systems use electronic
Power electronics
Power electronics is the application of solid-state electronics for the control and conversion of electric power.-Introduction:Power electronic converters can be found wherever there is a need to modify a form of electrical energy...

 devices like mercury arc valve
Mercury arc valve
A mercury-arc valve is a type of electrical rectifier used for converting high-voltage or high-current alternating current into direct current . Rectifiers of this type were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for...

s, thyristor
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...

s or IGBTs that were unavailable during the War of Currents era. Power is still converted to and from alternating current at each side of the modern HVDC link. The advantages of HVDC over AC systems for bulk transmission include higher power ratings for a given line (important since installing new lines and even upgrading old ones is extremely expensive) and better control of power flows, especially in transient and emergency conditions that can often lead to blackouts. Many modern plants now use HVDC as an alternative to AC systems for long distance, high load transmission, especially in developing countries such as China, India and Brazil. (See List of HVDC projects for more details.)

While DC distribution systems over significant distances are essentially extinct, DC power is still common when distances are small, and especially when energy storage or conversion uses batteries or fuel cells. These applications include:
  • Electronics
    Electronics
    Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

    , including Integrated circuit
    Integrated circuit
    An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

    s, high-power transmitter
    Transmitter
    In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

    s and computer
    Computer
    A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

    s
  • Vehicle starting, lighting, and ignition systems
    Car battery
    An automotive battery is a type of rechargeable battery that supplies electric energy to an automobile. Usually this refers to an SLI battery to power the starter motor, the lights, and the ignition system of a vehicle’s engine...

  • Hybrid
    Hybrid electric vehicle
    A hybrid electric vehicle is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional...

     and all-electric vehicle propulsion with internal power-supply
  • Telecommunication
    Telephone
    The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

     plant power (wired and cellular mobile)
  • Uninterruptible power
    Uninterruptible power supply
    An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...

     for computer systems
  • Utility-scale battery systems
    Grid energy storage
    Grid energy storage refers to the methods used to store electricity on a large scale within an electrical power grid. Electrical energy is stored during times when production exceeds consumption and the stores are used at times when consumption exceeds production...

  • "Off-grid
    Off-the-grid
    The term off-the-grid or off-grid refers to living in a self-sufficient manner without reliance on one or more public utilities....

    " isolated power installations using wind or solar power


In these applications, direct current may be used directly or converted to alternating current using power electronic devices
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....

. In the future, this may provide a way to supply energy to a grid from distributed sources. For example, hybrid vehicle owners may rent the capacity of their vehicle's batteries for load-levelling purposes by the local electrical utility company.

International War of Currents





The International Electro-Technical Exhibition of 1891
International Electro-Technical Exhibition - 1891
The 1891 International Electro-Technical Exhibition was held between 16 May and 19 October on the disused site of the three former “Westbahnhöfe” in Frankfurt am Main. The exhibition featured the first long distance transmission of high-power, three-phase electrical current, which was generated...

 featured the long distance transmission of high-power, three-phase electric current. It was held between 16 May and 19 October on the disused site of the three former “Westbahnhöfe” (Western Railway Stations) in Frankfurt am Main. The exhibition featured the first long distance transmission of high-power, three-phase electric current, which was generated 175 km away at Lauffen am Neckar. As a result of this successful field trial, three-phase current became established for electrical transmission networks throughout the world.

As far as Germany was concerned, the International Electro-Technical Exhibition settled once and for all the question of the most economical means of transmitting electrical energy. When the exhibition closed, the power station
Power station
A power station is an industrial facility for the generation of electric energy....

 at Lauffen continued in operation, providing electricity for the administrative capital, Heilbronn, making it the first place to be equipped with three-phase AC power.

See also



  • General: Electricity
    Electricity
    Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

  • Alternating current
    Alternating current
    In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

  • Direct current
    Direct current
    Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

  • Extra-low voltage
  • AC advocates:
    • Nikola Tesla
      Nikola Tesla
      Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...

    • Sebastian Ziani de Ferranti
      Sebastian Ziani de Ferranti
      Sebastian Pietro Innocenzo Adhemar Ziani de Ferranti was an electrical engineer and inventor.-Personal life:...

    • George Westinghouse
      George Westinghouse
      George Westinghouse, Jr was an American entrepreneur and engineer who invented the railway air brake and was a pioneer of the electrical industry. Westinghouse was one of Thomas Edison's main rivals in the early implementation of the American electricity system...

    • Charles Proteus Steinmetz
      Charles Proteus Steinmetz
      Charles Proteus Steinmetz was a German-American mathematician and electrical engineer. He fostered the development of alternating current that made possible the expansion of the electric power industry in the United States, formulating mathematical theories for engineers...

    • Charles F. Scott
    • Miksa Déri
      Miksa Déri
      Miksa Déri was a Hungarian electrical engineer. He was, with his partners Károly Zipernowsky and Ottó Bláthy, co-inventor of the closed iron core transformer and the ZBD model AC electrical generator....

       of Ganz
      Ganz
      The Ganz electric works in Budapest is probably best known for the manufacture of tramcars, but was also a pioneer in the application of three-phase alternating current to electric railways. Ganz also made / makes: ships , bridge steel structures , high voltage equipment...

      , Hungary
    • Ottó Bláthy
      Ottó Bláthy
      Ottó Titusz Bláthy was a Hungarian electrical engineer. In his career, he became the co-inventor of the modern electric transformer, the tension regulator, , the AC watt-hour meter, the single-phase alternating current electric motor, the turbo generator, and the high efficiency turbo...

       of Ganz, Hungary
  • DC advocates:
    • Thomas Edison
      Thomas Edison
      Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...

    • Arthur Kennelly
    • Harold P. Brown
      Harold P. Brown
      Harold Pitney Brown was the American credited with building the original electric chair based on the design by Dr. Alfred P. Southwick...

    • Lord Kelvin
      William Thomson, 1st Baron Kelvin
      William Thomson, 1st Baron Kelvin OM, GCVO, PC, PRS, PRSE, was a mathematical physicist and engineer. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging...


Further reading

  • Berton, Pierre (1997). Niagara: a history of the Falls. New York: Kodansha International.
  • Beyer, Rick (2003). The greatest stories never told: 100 tales from history to astonish, bewilder, & stupefy. New York: HarperResource. Pages 122 - 123.
  • Bordeau, Sanford P. (1982). Volts to Hertz—the rise of electricity: from the compass to the radio through the works of sixteen great men of science whose names are used in measuring electricity and magnetism. Minneapolis, Minn: Burgess Pub. Co.
  • Brandon, Craig (1999). The electric chair: an unnatural American history. Jefferson, N.C.: McFarland & Co.
  • Brands, Henry William (1995). The reckless decade: America in the 1890s. New York: St. Martin's Press.
  • Cheney, Margaret, Uth, Robert, & Glenn, Jim (1999). Tesla, master of lightning. New York: MetroBooks.
  • Conot, Robert, A Streak of Luck: The Life and Legend of Thomas Alva Edison. New York: Seaview Books,
  • Dobson, K., & Roberts, M. D. (2002). Physics: teacher resource pack. Cheltenham: Nelson Thornes.
  • Dommermuth-Costa, C. (1994). Nikola Tesla: a spark of genius. Minneapolis: Lerner Publications Co.
  • Edquist, Charles, Hommen, Leif, & Tsipouri, Lena J. (2000). Public technology procurement and innovation. Economics of science, technology, and innovation, v. 16. Boston: Kluwer Academic.
  • The Electrical Engineer, "A new system of alternating current motors and transformers". (1884). London: Biggs & Co. Pages 568 - 572.
  • The Electrical Engineer, "Practical electrical problems at Chicago". (1884). London: Biggs & Co. Pages 458 - 459, 484 - 485, and 489 - 490.
  • Foster, Abram John (1979). The coming of the electrical age to the United States. New York: Arno Press.
  • Mats Fridlund & Helmut Maier, The second battle of the currents: a comparative study of engineering nationalism in German and Swedish electric power, 1921-1961.
  • Hughes, Thomas Parke (1983). Networks of power: electrification in Western society, 1880-1930. Baltimore: Johns Hopkins University Press.
  • Tom McNichol AC/DC: the savage tale of the first standards war,John Wiley and Sons, 2006 ISBN 0-7879-8267-9
  • Munson, Richard (2005). From Edison to Enron: the business of power and what it means for the future of electricity. Westport, Conn: Praeger Publishers.
  • Reynolds, Terry S., and Bernstein, Theodore. “Edison and the Chair,” IEEE Technology and Society Magazine, March 1989, pp. 19–28.
  • Seifer, Marc J. (1998). Wizard: the life and times of Nikola Tesla : biography of a genius. Secaucus, N.J.: Carol Pub.
  • Silverberg, Robert, Light for the World, Edison and the Electric Power Industry. Princeton: Van Nostrand, 1967, pp. 229–243.
  • Scholnick, Robert J. (1992). American literature and science. Lexington: University Press of Kentucky. Pages 157 - 171.
  • Schurr, Sam H., Burwell, Calvin C., Devine, Warren D., Sonenblum, Sidney (1990). Electricity in the American economy: agent of technological progress. Contributions in economics and economic history, no. 117. New York: Greenwood Press.
  • Walker, James Blaine (1949). The epic of American industry. New York: Harper.
  • Westinghouse Electric Corporation, "Electric power transmission patents; Tesla polyphase system. (Transmission of power; polyphase system; Tesla patents)
  • Westinghouse Electric & Manufacturing Company, Collection of Westinghouse Electric and Manufacturing Company contracts, Pittsburgh, Pa.

External links