Information about War Of Currents

| In the "War of Currents" era (sometimes, "War of the Currents" or "Battle of Currents") in the late 1880s, George Westinghouse and Thomas Edison became adversaries due to Edison's promotion of direct current (DC) for electric power distribution over the alternating current (AC) advocated by Westinghouse and Nikola Tesla.

Introduction

During the initial years of electricity distribution, Edison's direct current was the standard for the United States and Edison was not disposed to lose all his patent royalties. Direct current worked to utilize incandescent lamps that were the principal load of the day, as well as for motors. Direct current systems could be directly used with storage batteries, providing valuable load-levelling and backup power during interruptions of generator operation. From his work with rotary magnetic fields, Tesla devised a system for generation, transmission, and use of AC power. He partnered with George Westinghouse to commercialize this system. Westinghouse had previously bought the rights to Tesla's polyphase system patents and other patents for AC transformers from Lucien Gaulard and John Dixon Gibbs.

Thomas Edison, American inventor and businessman, was known as "The Wizard of Menlo Park" and pushed for the development of a DC power network.

George Westinghouse, American entrepreneur and engineer, backed financially the development of a practical AC power network.

Nikola Tesla, Serbian-American inventor, physicist, and electro-mechanical engineer, was known as "The Wizard of The West"[1] and was instrumental in developing AC networks.

Several undercurrents lay beneath this rivalry. Edison was a brute-force experimenter, but was no mathematician. AC cannot really be understood or exploited without a substantial understanding in mathematics and mathematical physics, which Tesla had. Tesla had worked for Edison but was undervalued (for example, when Edison first learned of Tesla's idea of alternating-current power transmission, he dismissed it: "[Tesla's] ideas are splendid, but they are utterly impractical."^[2]). Bad feelings were exacerbated because Tesla had been cheated by Edison of promised compensation for his work.^[3][4] Edison would later come to regret that he had not listened to Tesla and utilized alternating current.^[5]

Electric power transmission

The competing systems

Edison's DC distribution system consisted of generating plants feeding heavy distribution conductors, with customer loads (lighting and motors) tapped off it. 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 electrocution.

To save on the cost of copper conductors, a three-wire 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" conductor, which only carried 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 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 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 transmitted, the wire size would be inversely proportional to the voltage used; or to put it another way, 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 DC system limitations was to generate power close to where it was consumed (today called, distributed generation) 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 building a local station^[6] or paying 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 for introducing electricity to many communities.

Direct current could not easily be changed to higher or lower voltages. This meant that separate electrical lines had to be installed in order to supply power to appliances that used different voltages, for example, lighting and electric motors. This led to a greater number of wires to lay and maintain, wasting money and introducing unnecessary hazards. A number of deaths from the Great Blizzard of 1888 were attributed to collapsing overhead power lines in New York City.^[7][8][9]

Alternating current could be transmitted over long distances at high voltages, at lower current for lower voltage drops (thus with 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 of 1887, it became clear that AC was the future of electric power distribution, although DC distribution was used in downtown metropolitan areas for decades thereafter.

Low frequency (50 - 60 Hz) AC currents can be more dangerous than similar levels of DC current since the alternating fluctuations can cause the heart to lose coordination, inducing ventricular fibrillation, which then rapidly leads to death within six to eight minutes from anemia of the brain and spinal cord. {[Wiggers CJ et al. 1940]}.. High voltage DC power can be more dangerous than AC, however, since it tends to cause muscles to lock in position, stopping the victim from releasing the energised conductor once grasped. 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. Since the precautions against electrocution are similar, ultimately, the advantages of AC power transmission outweighed this theoretical risk, and it was eventually adopted as the standard worldwide.

Transmission loss

The advantage of AC for distributing power over a distance is due to the ease of changing voltages with a transformer. Power is the product of current x voltage (P = IV). 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 a certain resistance, some power will be wasted as heat in the wires. This power loss is given by P = I²R. Thus, if the overall transmitted power is the same, and given the constraints of practical conductor sizes, low-voltage, high-current transmissions will suffer a much greater power loss than high-voltage, low-current ones. This holds whether DC or AC is used. However, it was very difficult to transform DC power to a high-voltage, low-current form efficiently, whereas with AC this can be done with a simple and efficient transformer. This was the key to the success of the AC system. Modern transmission grids regularly use AC voltages up to 765,000 volts ^[10]

Alternating current transmission lines do have other losses not observed with direct current. Due to the skin effect, 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 on the order of thousands of amperes. The increased resistance due to skin effect can be offset by changing the shape of conductors.

Current Wars

Edison's publicity campaign

Edison carried out a campaign to discourage the use^[11] of alternating current, including spreading information on fatal AC accidents, killing animals, and lobbying against the use of AC in state legislatures. Edison directed his technicians, primarily Arthur Kennelly and Harold P. Brown,^[12] to preside over several AC driven executions of animals, primarily stray cats and dogs, but also unwanted cattle and horses. Acting on these directives, there were demonstration to the press that alternating current was more dangerous than his system of direct current.^[13] Edison's series of animal executions peaked with the electrocution of Topsy the Elephant. He also tried to popularize the term for being electrocuted as being "Westinghoused".

Edison opposed capital punishment, but his desire to disparage the system of alternating current led to the invention of the electric chair. Harold P. Brown, who was at this time being secretly paid by Edison, constructed the first electric chair for the state of New York in order to promote the idea that alternating current was deadlier than DC.^[14]

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

Experts announced proposals to harness Niagara Falls for generating electricity, even briefly considering compressed air as a power transmission medium. Against General Electric and Edison's proposal, Tesla's AC system won the international Niagara Falls Commission contract. The commission was led by Lord Kelvin and backed by entrepreneurs such as J. P. Morgan, Lord Rothschild, and John Jacob Astor IV. Work began in 1893 on the Niagara Falls generation project and Tesla's technology was applied to generate electric power from the falls. It took five years to complete the facility.

Some doubted that the system would generate enough electricity to power industry in Buffalo. Tesla was sure it would work, saying that Niagara Falls had the ability to power the entire eastern U.S. On November 16, 1896, electrical power was sent from Niagara Falls to industries in Buffalo from the hydroelectric generators at the Edward Dean Adams Station. The hydroelectric 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, the contract to construct the transmission lines to Buffalo using the Tesla patents were given to them.^[15]

Although Tesla set the 60 Hertz standard for North America, the initial installation at Niagara was 25 Hz; a lower frequency was preferred for rotating machinery use, and the turbines at Niagara had been selected with a speed that was unsuitable for a 30 Hz winding. Eventually nearly all 25- Hz loads fed from Niagara were converted to 60 Hz, although 25 Hz facilities still exist.

Competition outcome

AC replaced DC for central station power generation and power distribution, enormously extending the range and improving the safety and efficiency of power distribution. Edison's low-voltage distribution system using DC ultimately lost to AC devices proposed by others: primarily Tesla's polyphase systems, and also other contributors, such as Charles Proteus Steinmetz (in 1888, he was working in Pittsburgh for Westinghouse^[16]). Tesla's Niagara Falls system was a turning point in the acceptance of alternating current. Eventually, Edison's General Electric company converted to the AC system and began manufacture of AC machines. Centralized power generation became possible when it was recognized that alternating current electric power lines can transport electricity at low costs across great distances by taking advantage of the ability to transform the voltage using power transformers.

Alternating current electricity distribution is today the penultimate stage in the delivery (before retail) of electricity to end users. It is generally considered to include medium-voltage (less than 50 kV) power lines, electrical substations and pole-mounted transformers, low-voltage (less than 1000 V) distribution wiring and sometimes electricity meters. Power transformers, installed at substations, could be used to raise the voltage from the generators and reduce it to supply loads. Increasing the voltage reduced the current in the transmission and distribution lines and hence the size of conductors required and distribution losses incurred. This made it more economical to distribute power over long distances. Generators (such as hydroelectric sites) could be located far from the loads.

Alternating current transmission was simpler; the processes involved were recognized as easier, faster and less expensive to implement. This allowed the rapid deployment of bulk transfer systems for electrical power from place to place to bring about the electrification of America. Typically, the main power transmission was between the power plant and a substation near a populated area. Due to the large amount of power involved, the transmission normally took place at high voltage and was transmitted over long distances through overhead high tension lines. Underground power transmission was used only in densely populated areas (such as large cities) because of the high cost of installation and maintenance and because the power losses increase dramatically compared with overhead transmission. Underground high voltage transmission uses much lower voltages to avoid discharge to the surrounding ground, and lower voltages require much thicker wires unless superconductors and cryogenic technology are used. Alternating current power transmission system grids today provide redundant paths and lines for power routing from any power plant to any load center, via any possible route, based on the economics of the transmission path, the cost of power and the perceived importance of keeping a particular load center powered at all times.

Engineers today design alternating current transmission networks in such a way as to transport the energy as efficiently as possible while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers, switches and transformers.

Remnant and existent DC systems

Some cities retained their DC networks for varying periods of time. For example, central Helsinki had a DC network until the late 1940s, and Stockholm lost its diminishing DC network in the ´60s. A mercury arc valve rectifier station would convert AC current for the downtown DC network. 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. In January 1998, Consolidated Edison began a program to eliminate DC service in its operating territory. At that time there were 5,400 DC customers. By 2006, there were only 60 customers using DC service, and by the beginning of 2007, all customers had been converted to AC service.

Most electric railways use a DC third-rail system, although trains powered by overhead pantographs use AC.

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 solid state devices 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 present HVDC over historic 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.

Direct current systems are still universally used in vehicles for engine starting, lighting, ignition, and battery charging. Twelve volt DC is the most common standard in automobiles, though the industry has announced plans to move to thirty-six volts DC (nominally forty-two volts at the bus) to reduce wire size requirements as more devices classically driven directly by the engine become all-electric, such as engine valves and air conditioning compressors, and new features such as heated windshields are added. Thirty-six volts was chosen because it is a margin below the highest safe voltage for accidental contact by personnel. Note that even on the scale of a single vehicle, the considerations of voltage drop and conductor size impel use of a higher voltage to meet higher load demands. Prior to the 1950s, vehicles used a six-volt system; the conversion to twelve-volt was made for essentially the same reasons.

Hybrid vehicles use banks of batteries and brushless DC motors^[17] to supplement the power of an internal combustion engine, improving both the fuel consumption and emissions performance of the vehicle. Additionally, small "off grid" isolated power installations using intermittent sources such as solar power, micro-hydro and wind turbines use DC at twelve, twenty-four or forty-eight volts and store energy in battery banks. Low-voltage lamps and appliances can be directly driven at the battery voltage, while standard AC electrical appliances can be powered with inverters that convert DC to AC.

Most telephone transmission and switching installations distribute DC power internally so that local battery banks can instantly assume the loads should external power sources fail. Negative forty-eight volt DC is the usual standard, though much cellular telephone radio equipment runs on twenty-four volt DC. This practice is followed in some Internet server and switching centers, especially those co-located with telephone equipment, though the development of the uninterruptible power supply has made it easier to use conventional AC-powered equipment in such critical applications. Computer systems generally operate with DC power, since logic circuits require it (a computer power supply converts AC to DC in most common applications). Some server farm engineers also prefer to deploy strictly DC power systems, arguing that doing so can improve heat efficiency and increase supply reliability .

Modern and future events

Since the rise of semiconductor technology, some basis for the predominance of alternating current has been altered. With current technology, the economics of DC voltage conversion has become somewhat attractive for specialized applications. Though AC predominates, there exist a number of high-voltage DC transmission lines throughout the world today. Many modern consumer loads in this century are increasingly more efficient requiring only low power source for everyday consumer electronics, batteries in phones/portable devices/gadgets or computer equipment. These can all be powered by a local renewable energy source, as advocated by Tesla in his later years, such as by solar micropower generation. The current demand context and options for easier local production thus avoids the distance transmission problems (which originally plagued the Edison system).

In popular culture

• The "War of the Currents" was part of the plot for the film The Prestige although the rivalry between Tesla and Edison was exaggerated and there was no mention of Westinghouse.
• "Edison's Medicine" was a song by the band Tesla from the album Psychotic Supper which features the War of Currents.
• The decision between AC and DC power was featured in the book "The Devil in the White City" by Erik Larson
• The 1980 movie "The Secret of Nikola Tesla" (aka Tajna Nikole Tesle) starring Orson Welles as J.P. Morgan depicts many of Tesla's achievements.

See also

General: Electricity

AC advocates: Nikola Tesla, Sebastian Ziani de Ferranti, George Westinghouse, Charles Proteus Steinmetz, Charles F. Scott

DC advocates: Thomas Edison, Arthur Kennelly, Harold P. Brown

References and articles

References

Further reading

Websites