In alternating current (AC, also ac) the movement (or flow) of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again. In 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 be through semiconductors, insulators, or even through a vacuum as in (DC), the movement (or flow) of electric charge is only in one direction.
Used generically, AC refers to the form in which electricity Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning and static electricity, but in addition, less familiar concepts, such as the electromagnetic field and electromagnetic induction is delivered to businesses and residences. The usual waveform Waveform means the shape and form of a signal such as a wave moving in a solid, liquid or gaseous medium or a vacuum of an 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. The portion of power that, averaged over a complete cycle of the AC waveform, results in net circuit is a sine wave The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields. Its most basic form as a function of time is:, however in certain applications, different waveforms are used, such as triangular A triangle wave is a non-sinusoidal waveform named for its triangular shape or square waves A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels. Audio An audio frequency , or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human. While the range of frequencies that any individual can hear is largely related to environmental factors, the generally accepted standard range of audible frequencies is 20 to 20,000 hertz. Frequencies below 20 Hz can and radio Radio frequency is a rate of oscillation in the range of about 30 kHz to 300 GHz, which corresponds to the frequency of electrical signals normally used to produce and detect radio waves. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems do exist (see mechanical filter and RF MEMS) signals carried on electrical wires are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated In electronics, modulation is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with respect to a modulating signal. This is done in a similar fashion as a musician may modulate a tone from a musical instrument by varying its volume, timing and pitch. The three key parameters of a) onto the AC signal.
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History
City lights viewed in a motion blurred Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation. It results when the image being recorded changes during the recording of a single frame, either due to rapid movement or long exposure exposure. The AC blinking causes the lines to be dotted rather than continuous. Westinghouse Early AC System 1887 (US patent 373035)A power 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 through the secondary winding. This varying magnetic developed by Lucien Gaulard Lucien Gaulard invented devices for the transmission of alternating current electrical energy and John Dixon Gibbs was demonstrated in London in 1881, and attracted the interest of Westinghouse Westinghouse Electric was an American power company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997. George Westinghouse had previously founded the Westinghouse Air Brake Company. They also exhibited the invention in Turin Turin (Italian: Torino, pronounced [toˈriːno] ; Piedmontese: Turin, pronounced [tyˈɾiŋ]) is a major city as well as a business and cultural centre in northern Italy, capital of the Piedmont region, located mainly on the left bank of the Po River surrounded by the Alpine arch. The population of the city proper is 909,193 (November 2008) while in 1884, where it was adopted for an electric lighting system. Many of their designs were adapted to the particular laws governing electrical distribution in the UK.[citation needed]
In 1882, 1884, and 1885 Gaulard and Gibbs applied for patents on their transformer; however, these were overturned due to prior arts of Nikola Tesla Nikola Tesla was an inventor, mechanical engineer, and electrical engineer. He was an important contributor to the birth of commercial electricity, and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries. Tesla's patents and theoretical work formed the basis of modern and actions initiated by Sebastian Ziani de Ferranti Sebastian Ziani de Ferranti was born in Liverpool, England. His Italian father, Cesare, was a photographer and his mother Juliana Scott Ferranti was a concert pianist. He was educated at Hampstead School, London; St. Augustine's College, Westgate on Sea; and University College London.
Ferranti Ferranti or Ferranti International plc was a major UK electrical engineering and equipment firm known primarily for defence electronics and power grid systems. The Company was once a constituent of the FTSE 100 Index but ceased trading in 1993 went into this business in 1882 when he set up a shop in London designing various electrical devices. Ferranti believed in the success of alternating current power distribution early on, and was one of the few experts in this system in the UK. In 1887 the London Electric Supply Corporation (LESCo) hired Ferranti for the design of their power station at Deptford. He designed the building, the generating plant and the distribution system. On its completion in 1891 it was the first truly modern power station, supplying high-voltage AC power that was then "stepped down" for consumer use on each street. This basic system remains in use today around the world. Many homes all over the world still have electric meters with the Ferranti AC patent stamped on them.
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 designed one of the first practical devices to transfer AC power efficiently between isolated circuits. Using pairs of coils wound on a common iron core, his design, called an induction coil An induction coil or "spark coil" is a type of disruptive discharge coil. It is a type of electrical transformer used to produce high-voltage pulses from a low-voltage DC supply. To create the flux changes necessary to induce voltage in the secondary, the DC current in the primary is repeatedly interrupted by a vibrating mechanical, was an early 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 through the secondary winding. This varying magnetic. The AC power system used today developed rapidly after 1886, and includes key concepts by Nikola Tesla Nikola Tesla was an inventor, mechanical engineer, and electrical engineer. He was an important contributor to the birth of commercial electricity, and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries. Tesla's patents and theoretical work formed the basis of modern, who subsequently sold his patent to 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. Westinghouse's system, which used alternating current based on the extensive research. Lucien Gaulard Lucien Gaulard invented devices for the transmission of alternating current electrical energy, John Dixon Gibbs, Carl Wilhelm Siemens Carl Wilhelm Siemens (4 April 1823 – 19 November 1883) was a German born engineer who for most of his life worked in Britain and later became a British subject and others contributed subsequently to this field. AC systems overcame the limitations of the 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 be through semiconductors, insulators, or even through a vacuum as in system used by Thomas Edison Thomas Alva Edison was an American inventor, scientist, and businessman who 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. Dubbed "The Wizard of Menlo Park" (now Edison, New Jersey) by a newspaper reporter, he to distribute electricity efficiently over long distances even though Edison attempted to discredit alternating current as too dangerous during the War of Currents In the "War of Currents" era 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 alternating current (AC) advocated by Westinghouse and Nikola Tesla.
The first commercial power plant in the United States using three-phase In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are 2π/3 radians offset in time. In this article angles will be measured in radians except where otherwise stated alternating current was at the Mill Creek No. 1 Hydroelectric Plant near Redlands, California Redlands is a city in San Bernardino County, California, United States. As of the 2000 census, the city had a total population of 63,591. The city is located 10 miles (16 km) east of downtown San Bernardino, in 1893 designed by Almirian Decker. Decker's design incorporated 10,000-volt three-phase transmission and established the standards for the complete system of generation, transmission and motors used today.
The Ames Hydroelectric Generating Plant (spring of 1891) and the original Niagara Falls The Niagara Falls are voluminous waterfalls on the Niagara River, straddling the international border between the Canadian province of Ontario and the U.S. state of New York. The falls are 17 miles north-northwest of Buffalo, New York and 75 miles (120 km) south-southeast of Toronto, Ontario, between the twin cities of Niagara Falls, Ontario, and Adams Power Plant Adams Power Plant Transformer House in Niagara Falls, New York is a National Historic Landmarked building constructed in 1895. It is the only remaining structure that was part of the historic Edward Dean Adams Power Plant, the first large-scale, alternating current electric generating plant in the world, built in 1895 (August 25, 1895) were among the first AC-powered hydroelectric plants.
The Jaruga Hydroelectric Power Plant Jaruga Hydroelectric Power Plant is a hydroelectric power plant on river Krka, located in Šibenik-Knin county, in central Dalmatia, Croatia in Croatia was set in operation on 28 August 1895. The two generators (42 Hz, 550 kW each) and the transformers were produced and installed by the Hungarian company 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 (Ganz Danubius), bridge steel structures (Ganz Acélszerkezet), high voltage equipment (Ganz Transelektro). Notable engineers. The transmission line from the power plant to the City of Šibenik Šibenik is a historic town in Croatia, with population of 51,553 (2001). It is located in central Dalmatia where the river Krka flows into the Adriatic Sea. Šibenik is a political, educational, transport, industrial and tourist center of Šibenik-Knin county was 11.5 kilometers (7.1 mi) long on wooden towers, and the municipal distribution grid 3000 V/110 V included six transforming stations.
Alternating current circuit theory developed rapidly in the latter part of the 19th and early 20th century. Notable contributors to the theoretical basis of alternating current calculations include Charles 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. He made ground-breaking discoveries in the understanding of hysteresis that, James Clerk Maxwell James Clerk Maxwell was a Scottish theoretical physicist and mathematician. His most important achievement was classical electromagnetic theory, synthesizing all previously unrelated observations, experiments and equations of electricity, magnetism and even optics into a consistent theory. His set of equations—Maxwell's equations—demonstrated, Oliver Heaviside Oliver Heaviside was a self-taught English electrical engineer, mathematician, and physicist who adapted complex numbers to the study of electrical circuits, invented mathematical techniques to the solution of differential equations (later found to be equivalent to Laplace transforms), reformulated Maxwell's field equations in terms of electric, and many others. Calculations in unbalanced three-phase systems were simplified by the symmetrical components In electrical engineering, the method of Symmetrical components is used to simplify analysis of unbalanced three phase power systems methods discussed by Charles Legeyt Fortescue Charles LeGeyt Fortescue was an electrical engineer. He was born in York Factory, in what is now Manitoba where the Hayes River enters Hudson Bay. He was the son of a Hudson's Bay Company fur trading factor and was among the first graduates of the Queen's University electrical engineering program in 1898 in 1918.
Transmission, distribution, and domestic power supply
Main articles: Electric power transmission Electric power transmission or "high voltage electric transmission" is the bulk transfer of electrical energy, from generating plants to substations located near to population centers. This is distinct from the local wiring between high voltage substations and customers, which is typically referred to as electricity distribution and Electricity distribution The modern distribution system begins as the primary circuit leaves the sub-station and ends as the secondary service enters the customer's meter socket. A variety of methods, materials, and equipment are used among the various utility companies, but the end result is similar. First, the energy leaves the sub-station in a primary circuit, usuallyAC voltage may be increased or decreased with a 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 through the secondary winding. This varying magnetic. Use of a higher voltage The voltage between two points is a short name for the electrical force that would drive an electric current between those points. Specifically, voltage is equal to energy per unit charge. In the case of static electric fields, the voltage between two points is equal to the electrical potential difference between those points. In the more general leads to significantly more efficient transmission of power. The power losses in a conductor are a product of the square of the current and the resistance The electrical resistance of an object is a measure of its attraction to the passage of a steady electric current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material of the conductor, described by the formula
This means that when transmitting a fixed power on a given wire, if the current is doubled, the power loss will be four times greater.
The power transmitted is equal to the product of the current and the voltage (assuming no phase difference); that is,
Thus, the same amount of power can be transmitted with a lower current by increasing the voltage. It is therefore advantageous when transmitting large amounts of power to distribute the power with high voltages (often hundreds of kilovolts).
High voltage transmission lines deliver power from electric generation For electric utilities, it is the first process in the delivery of electricity to consumers. The other processes, electric power transmission, electricity distribution, and electrical power storage and recovery using pumped storage methods are normally carried out by the electrical power industry plants over long distances using alternating current. These lines are located in eastern Utah Utah is one of the most religiously homogeneous states in the Union. Between 41% and 60% of Utahns are reported to be members of The Church of Jesus Christ of Latter-day Saints , which greatly influences Utah culture and daily life.However, high voltages also have disadvantages, the main one being the increased insulation required, and generally increased difficulty in their safe handling. In a power plant A power station is an industrial facility for the generation of electric power, power is generated at a convenient voltage for the design of a generator In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. The reverse conversion of electrical energy into mechanical energy is done by a motor; motors and generators have many similarities. A generator forces electrons in the windings to flow through the external electrical circuit. It is, and then stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary depending on the country and size of load, but generally motors and lighting are built to use up to a few hundred volts between phases.
The utilization voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems The lettering system used here is from a U.S. government document, which defines the letter names and gives a list of what plug types are used where. Although useful for quick reference, the document is ambiguous in some areas. A plug and socket that are classified here under the same letter will usually mate, but there is no guarantee of this. A found in the world.
Modern high-voltage, direct-current electric power transmission systems contrast with the more common alternating-current systems as a means for the efficient bulk transmission of electrical power over long distances. HVDC systems, however, tend to be more expensive and less efficient over shorter distances than transformers. Transmission with high voltage direct current was not feasible when Edison, Westinghouse and Tesla were designing their power systems, since there was then no way to economically convert AC power to DC and back again at the necessary voltages.
Three-phase electrical generation is very common. Three separate coils in the generator stator are physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other.
If the load on a three-phase system is balanced equally among the phases, no current flows through the neutral point. Even in the worst-case unbalanced (linear) load, the neutral current will not exceed the highest of the phase currents. Non-linear loads (e.g. computers) may require an oversized neutral bus and neutral conductor in the upstream distribution panel to handle harmonics. Harmonics can cause neutral conductor current levels to exceed that of one or all phase conductors.
For three-phase at utilization voltages a four-wire system is often used. When stepping down three-phase, a transformer with a Delta (3-wire) primary and a Star (4-wire, center-earthed) secondary is often used so there is no need for a neutral on the supply side.
For smaller customers (just how small varies by country and age of the installation) only a single phase and the neutral or two phases and the neutral are taken to the property. For larger installations all three phases and the neutral are taken to the main distribution panel. From the three-phase main panel, both single and three-phase circuits may lead off.
Three-wire single phase systems, with a single center-tapped transformer giving two live conductors, is a common distribution scheme for residential and small commercial buildings in North America. This arrangement is sometimes incorrectly referred to as "two phase". A similar method is used for a different reason on construction sites in the UK. Small power tools and lighting are supposed to be supplied by a local center-tapped transformer with a voltage of 55 V between each power conductor and earth. This significantly reduces the risk of electric shock in the event that one of the live conductors becomes exposed through an equipment fault whilst still allowing a reasonable voltage of 110 V between the two conductors for running the tools.
A third wire, called the bond (or earth) wire, is often connected between non-current-carrying metal enclosures and earth ground. This conductor provides protection from electric shock due to accidental contact of circuit conductors with the metal chassis of portable appliances and tools. Bonding all non-current-carrying metal parts into one complete system ensures there is always a low electrical impedance path to ground sufficient to carry any fault current for as long as it takes for the system to clear the fault. This low impedance path allows the maximum amount of fault current, causing the overcurrent protection device (breakers, fuses) to trip or burn out as quickly as possible, bringing the electrical system to a safe state. All bond wires are bonded to ground at the main service panel, as is the Neutral/Identified conductor if present.
AC power supply frequencies
Further information: Mains power around the worldThe frequency of the electrical system varies by country; most electric power is generated at either 50 or 60 Hz. Some countries have a mixture of 50 Hz and 60 Hz supplies, notably Japan.
A low frequency eases the design of low speed electric motors, particularly for hoisting, crushing and rolling applications, and commutator-type traction motors for applications such as railways, but also causes a noticeable flicker in incandescent lighting and an objectionable flicker in fluorescent lamps. 16⅔ Hz power is still used in some European rail systems, such as in Austria, Germany, Norway, Sweden and Switzerland. The use of lower frequencies also provided the advantage of lower impedance losses, which are proportional to frequency. The original Niagara Falls generators were built to produce 25 Hz power, as a compromise between low frequency for traction and heavy induction motors, while still allowing incandescent lighting to operate (although with noticeable flicker); most of the 25 Hz residential and commercial customers for Niagara Falls power were converted to 60 Hz by the late 1950s, although some 25 Hz industrial customers still existed as of the start of the 21st century.
Off-shore, military, textile industry, marine, computer mainframe, aircraft, and spacecraft applications sometimes use 400 Hz, for benefits of reduced weight of apparatus or higher motor speeds.
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Fri, 06 Aug 2010 18:18:08 GMT+00:00
Firedoglake (blog) Most of the power that travels over long distances is in the form of alternating current stepped up to very high voltages. There is now the ability to send ...
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Another impedance matching transformer can be seen on this printed circuit board in the upper right corner to the immediate left of resistors R2 and R1 It is labeled T1 Transformers can also be used in electrical instrumentation systems Due to transformers ability to step up or step down voltage and current and the electrical isolation they
michaelstorms
Wed, 11 Aug 2010 13:06:14 GM
Ac motors or . alternating current. motors are those which are driven by an . alternating current. . This type of motor is made up of two elements, the exterior, limited stator with coils supplied with an . alternating current. to formulate a ...
Q. Alternating current (AC), rather than direct current (DC), is used for the distribution of electric power. Answer true or false. DC transformers are useful for transmission of electric power. AC transformers are necessary to produce low voltage for consumers. Very high voltage has greatest efficiency for distribution of electric power. Transformers can change the voltage for AC. Edison promoted the use of AC. All electric generators produce AC.
Asked by kcguy13@prodigy.net - Tue Oct 28 15:38:18 2008 - - 1 Answers - 0 Comments
A. 1, True, AC is used for power distribution. 2. False. A transformer is an AC device. 3. True. 4. True. The higher the voltage, the lower the current. Losses in the wire depend on the current flow, not the voltage. This is why transmission lines run at very high voltages (200-700KV) and distribution lines (the wires at the top of the telephone poles) run at 13 KV or so. 5. True (Transformers can change AC voltages). 6. False. Edison liked DC, Tesla liked AC. AC won out, because of the transformer issue. Particularly at that time there was no practical way to step-up or step down DC voltages. 7. For commercial electric power, this is true. However, there are generators which can produce DC, so in a general sense, this is false.… [cont.]
Answered by mark p - Tue Oct 28 15:55:08 2008
