Incandescent lamps plus the AC / DC Debate
Swan, Edison and Tesla
Sir Joseph Wilson Swan
A Yorkshireman, Joseph Swan was one of the earliest credited inventors of an electrically operated incandescent lamp. He began experimenting with the phenomena of incandescence for illumination purposes in the 1840's and obtained a United Kingdom patent covering a partial vacuum, carbon filament incandescent lamp in 1860. Swan's early lamps provided low light output, were short lived, and were operated from battery cells.
Because of being operated from low voltage sources, relatively high filament current was required to deliver useful power to the lamps. In turn, the electrical current requirement necessitated that the power source be co-located near the Swan lamp. Otherwise, unacceptable transmission losses resulted, due to the resistance losses of the copper wires delivering the power to the lamps.
Due to this "line loss" penalty (i.e., the I2R power losses of the copper conductors) it was impractical to economically distribute low voltage battery power over any significant distance. Hence, Swanís early incandescent lamps were limited in application because of the co-location of the power source with the consuming device, or the alternative of incurring excessive line losses, made the initial Swan concept too expensive for general application.
Swan's low voltage lamp co-located power source survives today in flashlights, vehicle lighting systems, remote and other niche applications. There were many rivals to Swan in the race to develop electric illumination as a replacement for gas lighting. Electric arcs became competitive with gas light as a useful light source for outdoor illumination, but were impractical for the amount of light required in interior spaces. The problem was how to effectively divide the electrically supplied light.
The need was to have lighting in different locations without having the problems of co-locating a power source with each lamp or having excessive transmission line losses if the power source were remoted. This became known as the "division of light" problem. It was soon recognized that electric power could be more efficiently distributed at a higher voltage than the low voltages usually associated with galvanic cell (battery) sources.
A given amount of power could be delivered through the same size copper conductors with less "resistance" loss, if higher voltages could be employed. For example, if an early 20 watt, 5 Volt Swan type of lamp existed, it would require 4 Amperes of electrical current (P=V x I). However, if a 20 watt, 100 volt lamp existed it would require only 0.2 Amperes of current.
Thus, if higher voltage lamps could be developed, the transmission losses could be reduced to the point where the electric power source could be remoted from the power consuming lamps without incurring excessive line distribution losses. By 1879 Swan had developed an approximation of the requirement.
Thomas Alva Edison
Thomas Alva Edison, while working on the improvement of the then available DC generators, contemplated their use in a centralized power generating station. At that time, electrical generators were called Dynamos and were widely used as the power source for free-air carbon arc lighting in street lighting.
The generated power would be fed into a tree like electrical distribution system for the yet to be invented higher voltage, lower current, incandescent lamp for interior space lighting remote from the generators. Others had recognized the need for a high voltage, low current lamp for use with a central power generating station and distribution system, but Edison was the first to resolve the "line loss" and lamp limitations satisfactorily.
In 1878, Edison began to develop incandescent lamps in a race to surpass Swan and the limitations of his lamps. Late in 1879 Edison discovered that a carbon filament remained physically stable in vacuo at the temperature required to emit useful light. This discovery led him to develop an improved vacuum pump which made possible the long sought viable "high resistance", i.e. 100 Ohms plus, filament type lamp.
The system concept of central generation of higher voltage DC power and the distribution of that power by copper wire to remote locations to solve the "division-of-light" problem became economically practical. While Edison was acclaimed for his advancement of the incandescent lamp, his important contribution was his concept of integrating the electrical generation, distribution, and the power consuming lamps to achieve a consistent set of requirements for each system element in order to optimize the total System. Edison was one of the first system engineers.
In September of 1882 Edison, using a steam engine to drive his "dynamos" to generate direct current (DC) electric power, opened the first commercial central power generating station on Pearl Street in New York City. It had 85 customers and 400 lamps on the two wire feeder-and-main system. Later, it was converted to the famous Edison three wire system which consisted of a positive potential line, an equal but negative potential line and a neutral line, usually at ground potential.
The DC power had the desirable characteristic of being continuous and non-varying, and was distributed to a specific load such as a lamp. The alternating current (AC) power that dominates the world today, was little more than an electrical curiosity at that time. In 1889, Edison's companies, including his electric light company, and the Sprague Electric Railway Company, merged to become the Edison General Electric Company. It later merged with Thomson-Houston Electric Company to become the General Electric Company (GE).
Nikola Tesla and the "Death Ray"
Another great inventor of that era was Nikola Tesla, a Serbian emigrant. Early in his career he worked for Edison, redesigning DC dynamos. After being turned down by Edison for a requested salary raise from $18.00 to $25.00 per month, Tesla offered to sell his inventions to Edison for $50,000. Edison jokingly rejected Tesla's offer, and Tesla resigned.
In 1887, Tesla formed his own company to exploit one of his conceived inventions, which was one of the truly great inventions of all time, i.e., the conceptual discovery of the rotating magnetic field and the adaptation of it to his polyphase induction motor. Further, it provided means for generating polyphase AC power which had the salient property of being continuous and non-varying in nature, as was DC power.
Tesla's work between 1888 and 1896 led to a series of patents which were acquired by the entrepreneur George Westinghouse, who founded the Westinghouse Electric Corporation based on the purchased Tesla patents. Today, almost all of the world's power is generated and distributed by some form of the Tesla polyphase AC system. Where applicable, the generated electrical power is turned back into mechanical energy by updated versions of the motors originally covered by the Tesla patents.
Tesla was never widely recognized in the U.S. for his outstanding inventive contributions, possibly, because of some of his more eccentric work, i.e., he attempted to develop a "death ray" and other strange inventions. Tesla's major contribution, the ability to economically generate polyphase AC power, gave the world a second source of continuous, non-varying electrical power.
A statue of Nikola Tesla stands on Goat Island, in the Niagara River at the precipice of Niagara Falls, in recognition of his grand contribution. The continuing success of the Niagara Falls Hydroelectric plant, which used the Tesla system, all but ended the so-called "AC v DC war" of that time in favor of AC. During that period, Edison, whose lighting patents had been acquired by the GE Company, stated that AC electric power was dangerous, not commercially practical, and refused to adopt or endorse it.
However, with George Westinghouse's advocacy, the Tesla AC system won out and the GE (Edison's) DC system for town and city lighting systems became obsolete by the turn of the 20th century. The economic value of the Tesla and Edison patents caused them to be the focus of much animosity and lawyers dug the trenches to form a legal battlefield.
Cooler heads recognized the no-win situation and Westinghouse and General Electric cooperated in an electric manufacturing duopoly which continued until the passage and implementation of the Clayton Antitrust Act in 1911 and the later formation of RCA during World War I, which together blunted the duopoly's control of electric and radio patents. One Tesla radio patent case continued until 1945, when the Supreme Court belatedly reversed over a quarter of a century of lower court rulings in favor of Tesla and against Marconi Wireless, by then a part of RCA.
Source: http://www.flexiwatt.com
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