Alternating current

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Alternating current ( AC ) is an electric current that periodically reverses direction, in contrast to direct current ( DC ) flowing in only one direction. Alternating current is a form in which electricity is delivered to business and residence, and it is a form of electrical energy that consumers typically use when they install kitchen utensils, televisions, fans, and electric lights to a wall outlet. The common DC power source is the battery cell in the flashlight. The abbreviations of AC and DC are often used only means alternating and directly , as when they modify the stream or voltage .

The usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangle or square wave. Audio and radio signals carried on the power cord are also examples of alternating current. This type of current back and forth information such as sound (audio) or image (video) is sometimes carried by modulation of the AC carrier signal. These currents usually alternate at higher frequencies than those used in power transmission.

Video Alternating current

Transmission, distribution and domestic power supply

Electrical energy is distributed as an alternating current because the AC voltage can be increased or lowered by the transformer. This allows power to be transmitted via power lines efficiently at high voltages, which reduces the energy lost as heat due to wire resistance, and turns into lower, safer, voltage to use. The use of higher voltages will result in a much more efficient power transmission. Power loss ( $Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{    Â   P                                    w                                            {\ displaystyle P _ {\ rm {w}}} (W) and the resistance (R) wire, described by the formula}

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{    Â   P                                    w                                      =                   I               Â 2                          R                 .               {\ displaystyle P _ {\ rm {w}} = I ^ {2} R \,.}  Â}

This means that when transmitting fixed power to a given wire, if the current is halved (ie a multiple voltage), the lost power will be four times less.

Daya yang ditransmisikan sama dengan produk arus dan tegangan (dengan asumsi tidak ada beda fasa); itu adalah,

${\ displaystyle P _ {rm {t}} = IV \ ,.} Â Â$

As a result, the power transmitted at higher voltages requires less loss-producing current than for the same power at lower voltages. Power is often transmitted at hundreds of kilovolts, and converted to 100 V - 240 V for domestic use.

High stresses have losses, such as increased insulation required, and generally increase the difficulty in safe handling. In a power plant, energy is generated at a convenient voltage for generator design, and then upgraded to high voltage for transmission. Near the load, the transmission voltage is lowered to the voltage used by the equipment. Consumer voltage varies somewhat depending on the state and size of the load, but generally motors and lamps are made to be used up to several hundred volts between phases. Voltages delivered to equipment such as lighting and motor loads are standardized, with a permissible voltage range where the equipment is expected to operate. Standard power usage voltages and percentage tolerances vary in the various power systems found in the world. High voltage electric current power transmission (HVDC) systems have become more feasible because the technology has provided an efficient way to convert DC power. Transmissions with high-voltage direct current are not feasible in the early days of power transmission, as there is no economically viable way to lower DC voltage for end-user applications such as incandescent lamps.

Three-phase electrical generation is very common. The simplest way is to use three separate spools on the stator generator, physically offset by an angle of 120 Â ° (one-third of the 360 ​​phases â € <â € <Â ° complete) to each other. Three current waveforms are produced equal in magnitude and 120 Â ° phase to each other. If the coil is added opposite to this (distance 60Ã, Â °), the coil produces the same phase with reversed polarity and thus can be easily connected together. In practice, a higher "command pole" is usually used. For example, a 12-pole machine will have 36 windings (10 Â ° distance). The advantage is that a lower rotational speed can be used to generate the same frequency. For example, a 2-pole machine runs at 3600 rpm and a 12-pole engine running at 600 rpm produces the same frequency; lower speeds are better for larger engines. If the load on a three phase system is evenly balanced between the phases, no current flows through a neutral point. Even in unbalanced (linear) unbalanced loads, neutral currents will not exceed the highest phase currents. Non-linear loads (eg the widely used switch mode power supply) may require neutral buses and large neutral conductors in the upstream distribution panel to handle harmonics. Harmonics may cause the current neutral conductor level to exceed one or all of the phase conductors.

For three phases the voltage utilization of the four-wire system is often used. When stepping down three phases, a transformer with a primary Delta (3-wire) and a 4-wire (4-wire, center-of-earth) center is often used so there is no need for neutral on the supply side. For smaller customers (how small it varies by country and age of installation) only one phase and neutral, or two phases and neutral, are brought to the property. For larger installations, the three phases and neutrals are brought to the main distribution panel. From a three-phase main panel, either a one or three-phase circuit can begin. Single-phase three-wire system, with a central tapped central transformer providing two live conductors, is a common distribution scheme for small residential and commercial buildings in North America. This setting is sometimes mistakenly referred to as "two phases". A similar method is used for different reasons on construction sites in the UK. Small electrical appliances and illumination should be supplied by a local tapped transistor with a voltage of 55 V between each electrical and earth conductor. This significantly reduces the risk of electric shock in the event that one live conductor is exposed through equipment error while still allowing a reasonable voltage of 110 V between two conductors to run the appliance.

A third wire, called a bonding wire (or earth), is often connected between a metal enclosure with no current and earth soil. This conductor provides protection from electric shock due to accidental contact of circuit conductors with metal chassis of equipment and portable devices. Combining any metal parts that do not carry current into a complete system ensures that there is always a low electrical impedance path to the ground sufficient to carry any fault current as long as it is necessary for the system to clear the error. This low impedance path allows the maximum amount of disruption current, causing overcurrent protection devices (breakers, fuses) to trip or burn as quickly as possible, bringing the electrical system to a safe state. All bond cables are grounded on the main service panel, such as the neutral/identifiable conductors if they exist.

Maps Alternating current

frequency of AC power supply

The frequency of the electrical system varies by country and sometimes in a country; most of the electrical power is generated at 50 or 60 Hertz. Some countries have a mixed supply of 50 Hz and 60 Hz, especially electric power transmission in Japan. Low frequency eases the design of electric motors, especially for lifting, crushing and rolling applications, and commutator type traction motors for applications such as railroads. However, low frequencies also cause flicker visible in arc lamps and incandescent light bulbs. The use of lower frequencies also gives the advantage of lower impedance losses, which are proportional to frequency. The original Niagara Falls generator was built to generate 25 Hz power, as a compromise between low frequency for traction and heavy induction motors, while still allowing incandescent light to operate (albeit with flicker visible). Most residential and commercial 25 Hz customers for the Niagara Falls were converted to 60 Hz by the late 1950s, although some 25 Hz industrial customers still existed at the beginning of the 21st century. 16.7 Hz power (formerly 16 2/3 Hz) is still used in some European rail systems, such as in Austria, Germany, Norway, Sweden and Switzerland. Off-shore, military, textile, marine, aircraft, and spacecraft applications sometimes use 400 Hz, for the benefit of weight reduction equipment or higher motor speed. Computer mainframe systems are often driven by 400 Hz or 415 Hz for the benefit of ripple reduction when using a smaller AC to DC conversion unit. In any case, the inputs to the MG sets are local indigenous voltages and frequencies, range of 200 V (Japan), 208 V, 240 V (North America), 380 V, 400 V or 415 V (Europe), and various 50 Hz or 60 Hz.

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High-frequency effects

Direct current flows uniformly across the uniform cross section of the wire. The alternating current of any frequency is forced away from the center of the wire, to the outer surface. This is because the acceleration of electrical charges in alternating current produces electromagnetic radiation waves which cancel the dissemination of electricity to the center of the material with high conductivity. This phenomenon is called skin effect. At very high frequencies the current no longer flows in the wire , but effectively flows on the surface of the wire, in thickness of some skin depth. The depth of the skin is a thickness where the current density is reduced to 63%. Even at relatively low frequencies used for power transmission (50 Hz - 60 Hz), uneven flow distributions still occur on fairly thick conductors. For example, the depth of the skin of a copper conductor is about 8.57 mm at 60 Hz, so high current conductors are usually perforated to reduce mass and cost. Since currents tend to flow on the periphery of the conductor, the effective conductor cross section is reduced. This increases the effective AC resistance of the conductor, since the resistance is inversely proportional to the cross-sectional area. AC resistance is often higher than DC resistance, causing a much higher energy loss due to ohmic heating (also called I ² R loss).

Technique to reduce AC resistance

For low to moderate frequencies, conductors can be divided into interlocked wires, each isolated from each other, and the relative position of the individual strands specially arranged in the conductor bundle. The wire built using this technique is called the Litz wire. This measure helps to partially reduce skin effect by forcing a more equal current across the total cross section of the spliced ​​conductor. The litz wire is used to make high-Q inductors, reducing losses in flexible conductors that carry very high currents at lower frequencies, and in rolls of devices carrying higher radio frequency currents (up to hundreds of kilohertz), such as switch mode power supplies and transformers radio frequency.

Techniques to reduce radiation loss

As noted above, alternating current is made of electrical charge under periodic acceleration, which causes electromagnetic wave radiation. The emitted energy is gone. Depending on the frequency, different techniques are used to minimize losses due to radiation.

Twisted pairs

At frequencies up to about 1 GHz, the cable pair is twisted together in a cable, forming a bent pair. This reduces the losses of electromagnetic radiation and inductive coupling. A twisted pair should be used with a balanced signal system, so both cables carry the same current but are opposite. Each wire in a pair of bends radiates a signal, but is effectively canceled by radiation from another cable, resulting in almost no radiation loss.

Coaxial cable

The coaxial cable is commonly used on audio frequencies and above for convenience. The coaxial cable has a conductive wire inside a conductive tube, separated by a dielectric layer. The current flowing on the inner surface of the conductor is the same and opposite to the current flowing on the inner surface of the outer tube. The electromagnetic field is thus entirely contained in the tube, and (ideally) no energy is lost due to radiation or coupling outside the tube. Coaxial cable has acceptable small losses for frequencies up to about 5 GHz. For microwave frequencies greater than 5 GHz, losses (mainly due to electrical resistance from central conductors) become too large, making waveguides a more efficient medium for transmitting energy. Coaxial cables with air rather than solid dielectrics are preferred because they transmit power with lower losses.

waveguides

Waveguides are similar to coaxial cables, because they are made up of tubes, with the biggest difference being that the waveguide has no inner conductor. Waveguides can have any arbitrary cross section, but rectangular sections are the most common. Since waveguides do not have an inner conductor to carry backflow, waveguides can not transmit energy through electric current, but by using electromagnetic fields guided . Although the surface current flows on the inner wall of the waveguides, the surface current does not carry power. Power is carried by a guided electromagnetic field. The surface current is governed by a guided electromagnetic field and has a field-keeping effect in the waveguide and prevents field leakage into the space outside the waveguide. Waveguides have dimensions that are proportional to the wavelength of the alternating current to be transmitted, so they are only feasible at microwave frequencies. In addition to this mechanical feasibility, the electrical resistance of the non-ideal metal that forms the waveguide wall causes power dissipation (the current flowing current on the lost power loss conductor). At higher frequencies, the power lost due to this dissipation becomes too large.

Fiber optics

At frequencies greater than 200 GHz, the waveguide dimension becomes impractical small, and the ohmic losses in the waveguide wall become large. In contrast, optical fibers, which are forms of dielectric waveguides, may be used. For such frequencies, the concept of voltage and current is no longer used.

src: ffden-2.phys.uaf.edu

Mathematics of AC voltage

Arus bolak disertai (atau disebabkan) oleh tegangan bolak-balik. Sebuah tegangan AC v dapat digambarkan secara matematis sebagai fungsi waktu dengan persamaan berikut:

${\ displaystyle v (t) = V _ {\ mathrm {peak}} \ cdot \ sin (\ omega t)} Â Â$ ,

dimana

• ${\ displaystyle \ displaystyle V _ {rm {peak}}} Â$ adalah tegangan puncak (satuan: volt),
• ${\ displaystyle \ displaystyle \ omega} Â$ adalah frekuensi sudut (unit: radian per detik)
  • Frekuensi angular terkait dengan frekuensi fisik, ${\ displaystyle \ displaystyle f} Â$ (unit = hertz), yang mewakili jumlah siklus by detik, dense persuasive ${\ displaystyle \ displaystyle \ omega = 2 \ pi f} Â Â$ .
• ${\ displaystyle \ displaystyle t} Â Â$ adalah waktu (unit: detik).

Hubungan antara tegangan dan daya yang dikirimkan adalah

${\ displaystyle p (t) = {\ frac {v2 (t)} {R}}} Â$ di mana ${\ displaystyle R} Â$ merepresentasikan resistansi beban.

To illustrate these concepts, consider the 230 V AC power supply used in many countries around the world. So called because the mean value of root is 230Ã,V. This means that the average time-wattage delivered is equivalent to the power delivered by the DC voltage of 230Ã,V. To determine the peak voltage (amplitude), we can reset the above equation to:

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{         V                                    p             e             a             k                                      =                       Â 2                          Ã,                 V                                     r             m              s                                      .               {\ displaystyle V _ {\ mathrm {peak}} = {\ sqrt {2}} \ V _ {\ mathrm {rms}}.}  Â}

Untuk 230 V AC, puncak ${\ displaystyle V _ {\ mathrm {peak}}} Â$ adalah ${\ displaystyle 230V \ times {\ sqrt {2}}} Â$ , yaitu sekitar 325Ã, V. Selama satu siklus, tegangan naik dari nol ke 325Ã, V, jatuh ke nol hingga -325Ã, V, dan kembali ke nol.

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Transmisi informasi

Alternating current is used to transmit information, as in the case of telephone and cable television. The information signal is done through various AC frequencies. The POT phone signal has a frequency of about 3 kHz, close to the baseband audio frequency. Cable television and information flows transmitted by cables can alternate at frequencies of tens to thousands of megahertz. This frequency is similar to the frequencies of electromagnetic waves that are often used to transmit the same type of information over the air.

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History

The first alternator for generating alternating current was a dynamo electric generator based on Michael Faraday's principle built by French instrument maker Hippolyte Pixii in 1832. Pixii then added the commutator to the tool to produce a more commonly used direct current. The earliest practical applications recorded from alternating current are by Guillaume Duchenne, inventor and developer of electrotherapy. In 1855, he announced that AC was superior to direct current to trigger muscle contraction electrotherapy. Alternating current technology was first developed in Europe due to the work of Guillaume Duchenne (1850s), Hungarian Ganz Works (1870s), and in the 1880s: Sebastian Ziani de Ferranti, Lucien Gaulard, and Galileo Ferraris.

In 1876, Russian engineer Pavel Yablochkov invented a lighting system in which induction coil sets were installed along high-voltage AC lines. Instead of changing the voltage, the main coil transfers power to a secondary winding connected to one or several 'electric candles' (arc lamps) of its own design, used to keep a single lamp failure from disabling the entire circuit. In 1878, the Ganz factory, Budapest, Hungary, began producing equipment for electric lighting and, in 1883, had installed more than fifty systems in Austria-Hungary. Their air conditioning systems use bows and incandescent lamps, generators, and other equipment.

Transformer

The alternating current system can use a transformer to change the voltage from low to high and back, allowing generation and consumption at low voltage but transmission, possibly at great distances, at high voltage, with savings in conductor cost and energy loss. A bipolar open-core power transformer developed by Lucien Gaulard and John Dixon Gibbs was demonstrated in London in 1881, and attracted Westinghouse. They also exhibited this discovery in Turin in 1884. However this initial induction coil with an open magnetic circuit is inefficient in transferring power to the load. Until about 1880, the paradigm for transmitting AC power from a high-voltage supply to a low-voltage load is a series circuit. An open core transformer with a ratio of near 1: 1 is connected to its predecessor in series to allow the use of high voltage for transmission while presenting low voltage to the lamp. The disadvantage inherent in this method is to turn off a single light (or other electrical device) affecting the voltage supplied to all others on the same circuit. Many adjustable transformer designs are introduced to compensate for the problematic characteristics of this circuit, including those using core tuning methods or by passing magnetic flux around the coil. The direct current system does not have this deficiency, giving a significant advantage over the initial AC system.

Pioneers

In the fall of 1884, KÃÆ'¡roly Zipernowsky, OttÃÆ'³ BlÃÆ'¡thy and Miksa DÃÆ' Â © ri (ZBD), three engineers associated with the Ganz plant, determined that the open-core devices were impractical, as they were unable to regulate the voltage. In their 1885 patent application together for a new transformer (later called ZBD transformers), they describe two designs with closed magnetic circuits in which copper windings either wound around the iron ring wire core or b) surrounded by iron core wire. In both designs, the magnetic flux connecting the primary and secondary windings is almost entirely within the boundary of the iron core, without a deliberate path through the air (see toroidal nucleus). The new Transformer is 3.4 times more efficient than the open-core Gaulard and Gibbs bipolar devices. The Ganz plant in 1884 sent five of the world's first high-efficiency AC transformers. This first unit has been produced with the following specifications: 1,400 W, 40 Hz, 120: 72 V, 11.6: 19.4 A, ratio 1.67: 1, single phase, shell shape.

ZBD patents include two other major interrelated innovations: one on the use of connected parallel, not connected series, load utilization, the other regarding the ability to have a transformer ratio change so high that supply chain voltage can be much higher (initially 1400 V to 2000Ã, V ) of the load utilization voltage (100 V initially desired). When used in parallel-connected power distribution systems, closed core transformers are finally technically and economically feasible to provide electricity for home, business and public spaces. Another important milestone was the introduction of the 'voltage source, voltage intensive' (VSVI) system 'by the invention of a constant voltage generator in 1885. OttÃÆ'³ BlÃÆ'¡thy also invented the first AC power meter.

The AC power system was developed and adopted rapidly after 1886 due to its ability to distribute electricity efficiently over long distances, overcoming the limitations of the direct current system. In 1886, ZBD engineers designed the world's first power plant that uses an AC generator to power a parallel-connected shared power grid, a Rome-Cerchi powered steam power plant. The reliability of AC technology received a boost after Ganz Works energized a major European metropolis: Rome in 1886.

In the UK, Sebastian de Ferranti, who has developed an AC and transformer generator in London since 1882, redesigned the air conditioning system at the Grosvenor Grosvenor power plant in 1886 for the London Electric Supply Corporation (LESCo) including its own design alternator and transformation. design similar to Gaulard and Gibbs. In 1890 he designed their power plant at Deptford and transformed the Grosvenor Gallery station across the Thames into an electrical substation, showing how to integrate older plants into a universal AC supply system.

In the US William Stanley, Jr. designing one of the first practical devices to efficiently transfer AC power between isolated circuits. Using a pair of wound coils on a common iron core, the design, called an induction coil, is an early transformer (1885). Stanley also works in engineering and adapting European designs such as the Gaulard and Gibbs transformers to US entrepreneur George Westinghouse who started building the air conditioning system in 1886. The spread of Westinghouse and other air conditioning systems sparked a boost in late 1887 by Edison (a direct current advocate) discrediting the current back and forth as too dangerous in a public campaign called "War of Currents". In 1888 the alternating current system obtained further viability with the introduction of functional AC motors, something that the system was lacking until then. Designs, induction motors, independently created by Galileo Ferraris and Nikola Tesla (with Tesla design licensed by Westinghouse in the US). The design was later developed into a modern three-phase practical form by Mikhail Dolivo-Dobrovolsky and Charles Eugene Lancelot Brown.

The Ames Hydroelectric Power Station (spring of 1891) and the original Niagara Falls Adams Power Plant (August 25, 1895) is one of the first hydroelectric hydroelectric power stations. The first single-phase electric transmission of a single phase comes from a hydroelectric plant in Oregon at Willamette Falls which in 1890 sent power fourteen miles downstream to downtown Portland for street lighting. In 1891, a second transmission system was installed in Telluride Colorado. The San Antonio Canyon generator is the third commercial single phase hydroelectric power plant in the United States to provide long-distance electricity. It was completed on December 31, 1892 by Almarian William Decker to provide electricity to the 14-mile-long town of Pomona, California. In 1893 he subsequently designed the first commercial three-phase power plant in the United States using alternating current is the No. 1 Hydroelectric Power Plant near Redlands, California. The Decker design incorporates a 10-kV double-phase transmission and sets the standard for complete generation, transmission and motor systems in use today. The Jaruga Hydroelectric Power Plant in Croatia was operated on 28 August 1895. Two generators (42 Hz, 550 kW each) and transformer were manufactured and installed by Hungarian Ganz company. The transmission line from the power plant to the City of ibenik is 11.5 kilometers (7.1 miles) long in the wood tower, and the 3000 V/110 V city distribution network includes six transformation stations. The theory of alternating current circuits developed rapidly in the later part of the 19th and early 20th centuries. Contributors essential to the theoretical basis of alternating current calculations include Charles Steinmetz, Oliver Heaviside, and many others. Calculations in an unbalanced three-phase system are simplified by symmetrical component methods discussed by Charles Legeyt Fortescue in 1918.

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See also

src: cf.ppt-online.org

References

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Further reading

src: cf.ppt-online.org

External links

• " AC/DC: What's the Difference? ". Miracle Edison Light, American Experience. (PBS)
• " AC/DC: Inside the AC Generator ". Miracle Edison Light, American Experience. (PBS)
• Kuphaldt, Tony R., " Lessons In Electrical Circuits: Volume II - AC ". March 8, 2003. (Design Science License)
• Nave, C. R., " Concept of Alternating Current Circuits ". HyperPhysics.
• " Alternating Current (AC) ". Magnetic Particle Inspection, No Testing Ensiklopedia Destructive.
• " Flow back and forth ". Analog Process Control Services.
• Hiob, Eric, " Trig and Vector applications to Alternating Flow ". British Columbia Institute of Technology, 2004.
• " Introduction to alternating current and transformers ". Integrated Publishing.
• Chan. Keelin, " Alternating current Tools ". JC Physics, 2002.
• Williams, Trip "Kingpin", " Understanding the Alternating Current, Some other power concepts ".
• " Voltage Table, Frequency, Broadcast TV system, Radio Broadcasting, by Country ".
• Professor Mark Celles's tour of the 25 Hz Rankine power station
• 50/60 hertz information
• AC Circuit Animation and explanation of vector representation (phasor) RLC circuit
• Blalock, Thomas J., " Frequency Change Era: Interconnecting Systems from Different Cycles ". History of various frequencies and interconversion schemes in the US at the beginning of the 20th century
• (in Italian) Generates an AC voltage. Interactive.
• AC Power and Timeline History

Source of the article : Wikipedia