Split-phase electric power

Fig. 3. Pole-mounted single-phase transformer with three-wire center-tapped "split-phase" secondary. One side of the primary is connected to ground. On the three secondary terminals, the center tap is also grounded with a short strap to the transformer case.

A split-phase or single-phase three-wire system is a type of single-phase electric power distribution. It is the AC equivalent of the original Edison three-wire direct-current system. Its primary advantage is that it saves conductor material over a single-ended single-phase system, while only requiring a single phase on the supply side of the distribution transformer.[1]

Current is transmitted in two sine waves, each of which is on its own "hot" wire, and each of which varies between +170 V (120 V rms) and -170 V (120 V rms) with respect to ground. Because the waves are 180° out of phase with each other, this means that when one is at a full +170 V, the other is at full -170 V, for a total of 240 V rms; both reach 0 V at the same time. When added together, this results in a circuit that supplies 240 V (rms) with the same frequency, but "split" across two hot wires rather than one hot and one neutral.

Connections
Fig. 1
Fig. 2

A transformer supplying a three-wire distribution system has a single-phase input (primary) winding. The output (secondary) winding is center-tapped and the center tap connected to a grounded neutral. As shown in Fig. 1. either end to center has half the voltage of end-to-end. Fig. 2 illustrates the phasor diagram of the output voltages for a split-phase transformer. Since the two phasors do not define a unique direction of rotation for a revolving magnetic field, a split single-phase is not a two-phase system.

In the United States, the practice originated with the DC distribution system developed by Thomas Edison. By connecting pairs of lamps or groups of lamps on the same circuit in series, and doubling the supply voltage, the size of conductors was reduced substantially.

The line to neutral voltage is half the line-to-line voltage. Lighting and small appliances are connected between a line wire and the neutral. Large appliances, such as cooking equipment, space heating, water pumps, clothes dryers, and air conditioners are connected across the two line conductors, requiring less current and smaller conductors than would be needed if the appliances were designed for the lower voltage. [2]

Fig. 4
Fig. 5

If the load were guaranteed to be balanced, then the neutral conductor would not carry any current and the system would be equivalent to a single-ended system of twice the voltage with the line wires taking half the current. This would not need a neutral conductor at all, but would be wildly impractical for varying loads; just connecting the groups in series would result in excessive voltage and brightness variation as lamps are switched on and off.

By connecting the two lamp groups to a neutral, intermediate in potential between the two live legs, any imbalance of the load will be supplied by a current in the neutral, giving substantially constant voltage across both groups. The total current carried in all three wires (including the neutral) will always be twice the supply current of the most heavily loaded half.

For short wiring runs limited by conductor ampacity, this allows three half-sized conductors to be substituted for two full-sized ones, using 75% of the copper of an equivalent single-phase system.

Longer wiring runs are more limited by voltage drop in the conductors. Because the supply voltage is doubled, a balanced load can tolerate double the voltage drop, allowing quarter-sized conductors to be used; this uses 3/8 the copper of an equivalent single-phase system.

In practice, some intermediate value is chosen. For example, if the imbalance is limited to 25% of the total load (half of one half) rather than the absolute worst-case 50%, then conductors 3/8 of the single-phase size will guarantee the same maximum voltage drop, totalling 9/8 of one single-phase conductor, 56% of the copper of the two single-phase conductors.

Balanced power

In a so-called balanced power system, an isolation transformer with a center tap is used to create a separate supply with conductors at a balanced Vnom/2 with respect to ground. The purpose of a balanced power system is to minimize the noise coupled into sensitive equipment from the power supply.

Unlike a three-wire distribution system, the grounded neutral is not distributed to the loads; only line-to-line connections at 120 V are used. A balanced power system is only used for specialized distribution in audio and video production studios, sound and television broadcasting, and installations of sensitive scientific instruments.

The U.S. National Electrical Code provides rules for technical power installations.[3] The systems are not to be used for general-purpose lighting or other equipment, and may use special sockets to ensure only approved equipment is connected to the system. Additionally, technical power systems pay special attention to the way the distribution system is grounded.

A risk of using a balanced power system, in an installation that also uses "conventional" power in the same rooms, is that a user may inadvertently interconnect the power systems together via an intermediate system of audio or video equipment, elements of which might be connected to different power systems.

Applications
Europe

In Europe, three-phase 230/400 V is most commonly used. However, 230/460 V, three-wire, single-phase systems are used to run farms and small groups of houses when only one (or sometimes two) of the three-phase high-voltage conductors is available. A split-phase final step-down transformer is often used, with the centre-tap earthed and the two halves usually supplying different buildings.

In the UK, electric tools and portable lighting at construction sites are required to be fed from a centre-tapped system with only 55 V between live conductors and the earth. This system is used with 110 V equipment and therefore no neutral conductor is needed. The intention is to reduce the electrocution hazard that may exist when using electrical equipment at a wet or outdoor construction site. Portable transformers that transform single-phase 240 V to this 110 V system are a common piece of construction equipment. Generator sets used for construction sites are equipped to supply it directly.

An incidental benefit is that the filaments of 110 V incandescent lamps used on such systems are thicker and therefore mechanically more rugged than those of 240 V lamps.

Oceania

In Australia and New Zealand, remote loads are connected to the grid using SWER (single-wire earth return) transmission lines, since it is cheapest to run only one wire. The primary of the transformer is connected between the high voltage line and earth, the secondary is a three-wire single-phase system as described here, the secondary voltage being 230/460 V. Single phase loads are split between the two circuits. Hot water services use both circuits.

North America

This three-wire single phase system is common in North America for residential and light commercial applications. Breaker panels typically have a two hot, a neutral (connected at the other end to the grounded center tap of a local transformer), and a ground wires feeding in from the local distribution grid. Circuit breakers then either create 120 V circuits by connecting one hot to neutral, or 240 V circuits by connecting the two hot wires. 120 V circuits are the most common, and used to power NEMA 1 and NEMA 5 outlets, and direct-wired lights and appliances. 240 V circuits are used only for high-demand applications, typically electric stoves, electric clothes dryers, and electric cars, and some space heaters, air conditioners, and water heaters. These use NEMA 10 or NEMA 14 outlets that are deliberately incompatible with the 120 V outlets.

Wiring regulations govern the application of split-phase circuits; since the neutral (return) conductor is not protected by a fuse or circuit breaker, a neutral wire can be shared only by circuits fed from opposite lines of the supply system. Two circuits from opposing lines may share a neutral if both breakers are connected by a bar so that both trip simultaneously ([4]NEC 210.4), this prevents 120 V from feeding across 240 V circuits.

Some buildings have 208 V three-phase power instead of split-phase, for high-capacity circuits.

Railways

In Sweden split-phase electric power is also used on some railways. The center tap is grounded, one pole is fed with an overhead wire section, while the other wire is used for another section.

Amtrak's 60 Hz traction power system in the Northeast Corridor between New York and Boston also uses split-phase power distribution. Two separate wires are run along the track, the contact wire for the locomotive and an electrically separate feeder wire. Each wire is fed with 25 kV with respect to ground, with 50 kV between them. Autotransformers along the track balance the loads between the contact and feeder wires, reducing resistive losses.

In the UK Network Rail are using autotransformers on all new 50 Hz electrification, and (as of 2014) are converting many old booster transformer [1] installations to autotransformers, to reduce energy losses [2] and exported electromagnetic interference, both of which increase when longer, heavier, or faster trains are introduced, drawing higher peak current from the supply. Note that booster transformers only "boost" the return of traction current through its intended path, the "return conductor", rather than randomly through the earth, and do not boost, but rather reduce, the available voltage at the train, and introduce additional losses. The autotransformer system enforces the traction return current taking its intended path, while reducing the transmission losses, and therefore achieves both required objectives, of controlling return current leakage to earth and ensuring low energy loss, simultaneously. There is an initial cost penalty, because the previous return conductor, insulated to a fairly modest voltage, must be replaced by an anti-phase feeder, insulated to 25 kV, and the autotransformers themselves are larger and more expensive than the previous booster transformers.

See also
References
  1. Terrell Croft and Wilford Summers (ed), American Electricians' Handbook, Eleventh Edition, McGraw Hill, New York (1987) ISBN 0-07-013932-6, chapter 3, pages 3-10, 3-14 to 3-22.
  2. Gonen, Turan. Electric Power Distribution System Engineering, 2nd ed. CRC Press, 2007, p. 284.
  3. NFPA 70, National Electrical Code 2005, National Fire Protection Association, Inc., Quincy, Massachusetts USA, (2005). no ISBN , articles 640 and 647
  4. http://ecmweb.com/code-basics/branch-circuits-part-1
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Commutator (electric)

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Commutator (electric)

Commutator in a universal motor from a vacuum cleaner. Parts: (A) commutator, (B) brush, (C) rotor (armature) windings, (D) stator (F) (field) windings, (E) brush guides A commutator is a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit. It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine. Two or more electrical contacts called "brushes" made of a soft conductive material like carbon press against the commutator, making sliding contact with successive segments of the commutator as it rotates. The windings (coils of wire) on the armature are connected to the commutator segments. Commutators are used in direct current (DC) machines: dynamos (DC generators) and many DC motors as well as universal motors. In a motor the commutator applies electric current to the windings. By reversing the current direction in the rotating win ...more...

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Polarization (waves)

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Unbalanced line

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Unbalanced line

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Hybrid

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Utility pole

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Utility pole

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Squeezed states of light

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Squeezed states of light

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Star quad cable

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Star quad cable

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ANSI device numbers

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ANSI device numbers

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DC motor

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DC motor

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Dabhol Power Station

Also see Dabhol Power Company and Enron Scandal Dabhol Power Station is located near Anjanwel village in Ratnagiri district in Maharashtra, India, about 160 kilometres (99 mi) south of Mumbai. The power station was a built by the Dabhol Power Company (DPC), which was a joint venture of Enron, General Electric, Bechtel and Maharashtra Power Development Corporation.[1] At the start of its construction in 1992, the Dabhol power station was the biggest foreign investment in India. The plant was mired in controversies of corruption and malpractices involving Enron and people at the highest political levels of the Indian and the United States (Clinton and Bush Administration) governments.[2] History Construction of the Dabhol Power Station was planned to be completed in two phases. The first phase was a 740 MW unit to use naphtha as the fuel. Construction started in 1992 and finally completed in May 1999.[3] The next phase was 1700 MW of units using liquefied natural gas (LNG) as fuel. At its height, the constru ...more...

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Transfer switch

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Residual-current device

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Capacitor

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War of the currents

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War of the currents

American inventor and businessman Thomas Edison established the first investor-owned electric utility in 1882, basing its infrastructure on DC power. American entrepreneur and engineer George Westinghouse introduced a rival AC-based power distribution network in 1886. The war of the currents (sometimes called battle of the currents) was a series of events surrounding the introduction of competing electric power transmission systems in the late 1880s and early 1890s. It included commercial competition, a debate over electrical safety, and a media/propaganda campaign that grew out of it, with the main players being the direct current (DC)–based Edison Electric Light Company and the alternating current (AC)–based Westinghouse Electric Company. It took place during the introduction and rapid expansion of the alternating current standard (already in use and advocated by several US and European companies[1]) and its eventual adoption over the direct current distribution system. Three aspects have been confl ...more...

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Current transformer

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Current transformer

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Industrial and multiphase power plugs and sockets

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Industrial and multiphase power plugs and sockets

Pin and sleeve connectors Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase systems, with high currents, or when protection from environmental hazards is required. Industrial outlets may have weatherproof covers, waterproofing sleeves, or may be interlocked with a switch to prevent accidental disconnection of an energized plug. Some types of connectors are approved for hazardous areas such as coal mines or petrochemical plants, where flammable gas may be present. Almost all three-phase power plugs have an earth (ground) connection, but may not have a neutral because three-phase loads such as motors do not need the neutral. Such plugs have only four prongs (earth, and the three phases). An example of a socket with neutral is the L21-30 (30 A) and the L21-20 (20 A) both of which have five pins (earth, neutral, and X, Y, Z phases). While some forms of power plugs ...more...

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High-voltage direct current

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High-voltage direct current

Long distance HVDC lines carrying hydroelectricity from Canada's Nelson River to this converter station where it is converted to AC for use in southern Manitoba's grid A high-voltage, direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway)[1][2][3][4] uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current (AC) systems.[5] For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links. HVDC uses voltages between 100 kV and 1,500 kV. HVDC allows power transmission between unsynchronized AC transmission systems. Since the power flow through an HVDC link can be ...more...

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Sustainable energy

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Single-wire earth return

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Single-wire earth return

SWER power line in Queensland Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line which supplies single-phase electric power from an electrical grid to remote areas at low cost. Its distinguishing feature is that the earth (or sometimes a body of water) is used as the return path for the current, to avoid the need for a second wire (or neutral wire) to act as a return path. Single-wire earth return is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps. It is also used for high-voltage direct current over submarine power cables. Electric single-phase railway traction, such as light rail, uses a very similar system. It uses resistors to earth to reduce hazards from rail voltages, but the primary return currents are through the rails.[1] History Lloyd Mandeno, OBE (1888–1973) fully developed SWER in New Zealand around 1925 for rural electrification. Although he termed it "Earth Working Single Wire Line", it ...more...

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Solar energy

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The source of Earth's solar power: the Sun Solar energy is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture, molten salt power plants and artificial photosynthesis.[1][2] It is an important source of renewable energy and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power and solar water heating to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light-dispersing properties, and designing spaces that naturally circulate air. The large magnitude of solar energy available makes it a highly appealing source of electricity. The United Nations Development Programme in its 2000 World Energy A ...more...

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Hybrid Synergy Drive

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Hybrid Synergy Drive

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Hybrid electric vehicle

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Hybrid electric vehicle

A hybrid electric vehicle (HEV) is a type of hybrid vehicle that combines a conventional internal combustion engine (ICE) system with an electric propulsion system (hybrid vehicle drivetrain). The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle or better performance. There is a variety of HEV types, and the degree to which each functions as an electric vehicle (EV) also varies. The most common form of HEV is the hybrid electric car, although hybrid electric trucks (pickups and tractors) and buses also exist. Modern HEVs make use of efficiency-improving technologies such as regenerative brakes which convert the vehicle's kinetic energy to electric energy, which is stored in a battery or supercapacitor. Some varieties of HEV use their internal combustion engine to generate electricity by spinning an electrical generator to either recharge their batteries or to directly power the electric drive motors; this combination is known as a motor–generat ...more...

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Busbar

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Busbar

1500 ampere copper busbars within a power distribution rack for a large building Busbar with plastic wrapping inside of a bus duct In electric power distribution, a busbar (also bus bar, and sometimes misspelled as buss bar or bussbar) is a metallic strip or bar, typically housed inside switchgear, panel boards, and busway enclosures for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment in battery banks. They are generally uninsulated, and have sufficient stiffness to be supported in air by insulated pillars. These features allow sufficient cooling of the conductors, and the ability to tap in at various points without creating a new joint. Design and placement The material composition and cross-sectional size of the busbar determine the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 square millimetres (0.016 sq in), but electrical substatio ...more...

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Nikola Tesla

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Nikola Tesla

Nikola Tesla (;[2] Serbo-Croatian: ; Serbian Cyrillic: Никола Тесла; 10 July 1856 – 7 January 1943) was a Serbian American[3][4][5] inventor, electrical engineer, mechanical engineer, physicist, and futurist who is best known for his contributions to the design of the modern alternating current (AC) electricity supply system.[6] Born and raised in the Austrian Empire, Tesla received an advanced education in engineering and physics in the 1870s and gained practical experience in the early 1880s working in telephony and at Continental Edison in the new electric power industry. He emigrated to the United States in 1884, where he would become a naturalized citizen. He worked for a short time at the Edison Machine Works in New York City before he struck out on his own. With the help of partners to finance and market his ideas, Tesla set up laboratories and companies in New York to develop a range of electrical and mechanical devices. His alternating current (AC) induction motor and related polyphase AC patents, l ...more...

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Rail transport

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Rail transport

Rail transport is a means of transferring of passengers and goods on wheeled vehicles running on rails, also known as tracks. It is also commonly referred to as train transport. In contrast to road transport, where vehicles run on a prepared flat surface, rail vehicles (rolling stock) are directionally guided by the tracks on which they run. Tracks usually consist of steel rails, installed on ties (sleepers) and ballast, on which the rolling stock, usually fitted with metal wheels, moves. Other variations are also possible, such as slab track, where the rails are fastened to a concrete foundation resting on a prepared subsurface. An Acela Express high-speed trainset passing Old Saybrook station on its way to Boston, Massachusetts. Two Canadian National diesel locomotives pull a southbound freight train on the Norfolk-Southern railroad, near Columbus, Ohio in the United States A GWR 7800 Class steam locomotive hauling the Cambrian Coast Express between London and Pwllheli in the United Kingdom Rollin ...more...

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Live-line working

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Live-line working

A lineman wearing equipment for hot glove work In electrical engineering, live-line working, also known as hotline maintenance, is the maintenance of electrical equipment, often operating at high voltage, while the equipment is energised. The first techniques for live-line working were developed in the early years of the 20th century, and both equipment and work methods were later refined to deal with increasingly higher voltages. In the 1960s, methods were developed in the laboratory to enable field workers to come into direct contact with high voltage lines. Such methods can be applied to enable safe work at the highest transmission voltages. Background Electrical hazards Electricity is hazardous: an electric shock from a current as low as 35 milliamps is sufficient to cause fibrillation of the heart in vulnerable individuals.[1] Even a healthy individual is at risk of falling from a high structure due to loss of muscle control. Higher currents can cause respiratory failure and result in extensive and li ...more...

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Coherence (physics)

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Coherence (physics)

In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. Coherence is an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets. Interference is the addition, in the mathematical sense, of wave functions. A single wave can interfere with itself, but this is still an addition of two waves (see Young's slits experiment). Constructive or destructive interferences are limit cases, and two waves always interfere, even if the result of the addition is complicated or not remarkable. When interfering, two waves can add togethe ...more...

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Power plant engineering

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Power plant engineering

Typical smokestacks of nuclear power plant Power plant engineering or power station engineering is a division of power engineering, and is defined as "the engineering and technology required for the production of central station electric power."[1] The field is focused on the generation of power for industries and communities, not for household power production. The field is an interdisciplinary field, using the theoretical base of both mechanical and electrical engineering. The engineering aspect of power plant management has evolved with technology and has become progressively more complicated. The introduction of nuclear technology and the progression of other existing technologies have allowed power to be created in more ways and on a larger scale than was previously possible. The assignment of different types of engineers to the design, construction, and operation of a new power plant is dependent on the type of system being built such as whether it is a nuclear power plant, hydroelectric plant, or sola ...more...

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Global Hybrid Cooperation

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Global Hybrid Cooperation

Global Hybrid Cooperation (formerly called Advanced Hybrid System 2 or AHS2) is a set of hybrid vehicle technologies jointly developed by General Motors, Daimler, and Chrysler LLC, with BMW joining in 2005. It uses 2 or 3 planetary gearsets in an automatic transmission: one on the internal combustion engine side (input split) paired with a second (output split), forming the compound split, and possibly one third additional planetary gearset to multiply the number of fixed gear ratios (up to 4). General Motors has stopped using the "AHS2" name as of 2006, preferring to call it simply a "two-mode hybrid system". This technology was named as "Technology of the Year" for 2007 by Automobile Magazine.[1] While Toyota's Hybrid Synergy Drive may appear similar in that it also combines the power from an Internal combustion engine (ICE) and a pair of electric motor-generators; however in its current form, Toyota uses only one planetary gearset providing only single mode functionality (i.e. input split only) using a s ...more...

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MainPower

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MainPower

MainPower New Zealand Limited is an electricity distribution company, based in Rangiora, New Zealand, responsible for electricity distribution to over 37,000 customers in the Canterbury Region north of the Waimakariri River.[1] MainPower was formed in 1994, after the Energy Companies Act 1992 required the North Canterbury Electric Power Board to reform into a commercial power company. More reforms in 1998 required electricity companies nationally to split their lines and retail businesses, with MainPower retaining its lines business and selling its retail business to Contact Energy. MainPower has initiated a number of local generation projects, including the Mount Cass Wind Farm (proposed)[2] and Cleardale Hydro Power Station (operating).[3] Electricity network MainPower has a total service area of 11,180 square kilometres (4,320 sq mi), covering the Waimakariri, Hurunui and Kaikoura districts. The area includes the towns of Kaiapoi, Rangiora, Oxford, Woodend, Pegasus, Amberley, Waipara, Culverden, Cheviot ...more...

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IEC 60038

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IEC 60038

IEC voltage range AC RMSvoltage (V) DC voltage (V) Defining risk High voltage > 1 000 > 1 500 Electrical arcing Low voltage 50 to 1 000 120 to 1 500 Electrical shock Extra-low voltage < 50 < 120 Low risk International Standard IEC 60038:1983 defines a set of standard voltages for use in low voltage and high voltage AC electricity supply systems. Low voltage Where two voltages are given below separated by "/", the first is the root-mean-square voltage between a phase and the neutral connector, whereas the second is the corresponding root-mean-square voltage between two phases (exception: the category shown below called "One Phase", where 240 V is the root-mean-square voltage between the two legs of a split phase). The three-phase voltages are for use in either four-wire (with neutral) or three-wire (without neutral) systems. Three-phase 50 Hz 230 V / 400 V (formerly 220/380V) 400 V / 690 V (formerly 380/660V) 1000 V (3 wire) Suppliers using 220 V / 380 V or 240 V / 415 V systems were ...more...

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R-410A

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R-410A

R-410A, sold under the trademarked names Suva 410A, Forane 410A, Puron, EcoFluor R410, Genetron R410A, and AZ-20, is a zeotropic, but near-azeotropic mixture of difluoromethane (CHF, called R-32) and pentafluoroethane (CHFCF, called R-125), which is used as a refrigerant in air conditioning applications. R-410A cylinders are colored pink.[1] Environmental effects Unlike alkyl halide refrigerants that contain bromine or chlorine, R-410A (which contains only fluorine) does not contribute to ozone depletion, and is therefore becoming more widely used, as ozone-depleting refrigerants like R-22 are phased out. However, it has a high global warming potential (1700 times the effect of carbon dioxide), similar to that of R-22. [2] Since R-410A allows for higher SEER ratings than an R-22 system, by reducing power consumption, the overall impact on global warming of R-410A systems will be substantially lower than that of R-22 systems due to reduced greenhouse gas emissions from power plants.[3] History R-410A was i ...more...

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Transformer types

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Transformer types

Circuit symbols Transformer with two windings and iron core. Transformer with three windings. The dots show the relative configuration of the windings. Transformer with electrostatic screen preventing capacitive coupling between the windings. An electric arc furnace the transformer has heavy copper bus for the low voltage winding, which can be rated for tens of thousands of amperes. They are immersed in oil for cooling and insulation, and are designed to survive frequent short circuits. A variety of types of electrical transformer are made for different purposes. Despite their design differences, the various types employ the same basic principle as discovered in 1831 by Michael Faraday, and share several key functional parts. Power transformer Laminated core Laminated core transformer This is the most common type of transformer, widely used in electric power transmission and appliances to convert mains voltage to low voltage to power electronic devices. They are available in power rat ...more...

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Joule heating

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Joule heating

A coiled heating element from an electric toaster, showing red to yellow incandescence Joule heating, also known as Ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law, also known as the Joule–Lenz law,[1] states that the power of heating generated by an electrical conductor is proportional to the product of its resistance and the square of the current: P ∝ I 2 R {\displaystyle P\propto I^{2}R} Joule heating affects the whole electric conductor, unlike the Peltier effect which transfers heat from one electrical junction to another. History James Prescott Joule first published in December 1840, an abstract in the Proceedings of the Royal Society, suggesting that heat could be generated by an electrical current. Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current flowing through the wire for a 30 minute period. By varying the current and ...more...

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Thyristor switched capacitor

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Thyristor switched capacitor

A thyristor switched capacitor (TSC) is a type of equipment used for compensating reactive power in electrical power systems. It consists of a power capacitor connected in series with a bidirectional thyristor valve and, usually, a current limiting reactor (inductor). The thyristor switched capacitor is an important component of a Static VAR Compensator (SVC),[1][2] where it is often used in conjunction with a thyristor controlled reactor (TCR). Static VAR compensators are a member of the Flexible AC transmission system (FACTS) family. Circuit diagram A TSC is usually a three-phase assembly, connected either in a delta or a star arrangement. Unlike the TCR, a TSC generates no harmonics and so requires no filtering. For this reason, some SVCs have been built with only TSCs .[3] This can lead to a relatively cost-effective solution where the SVC only requires capacitive reactive power, although a disadvantage is that the reactive power output can only be varied in steps. Continuously variable reactive power o ...more...

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Antenna (radio)

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Antenna (radio)

In radio, an antenna is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.[1] In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment, and are used in radio broadcasting, broadcast television, two-way radio, communications receivers, radar, cell phones, satellite communications and other devices. An antenna is an array of conductors (elements), electrically connected to the receiver or transmitter. During transmission, the oscillating current applied to the antenna by a transmitter creates an oscillating electric field and magnetic field around th ...more...

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Dabhol Power Company

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Dabhol Power Company

Also See Dabhol Power Station and Enron Scandal The Dabhol Power Company (now called RGPPL - Ratnagiri Gas and Power Private Limited) was a company based in Maharashtra, India, formed in 1992 to manage and operate the controversial Dabhol Power Plant.[1] The Dabhol plant was built through the combined effort of Enron, GE, and Bechtel. GE provided the generating turbines to Dabhol, Bechtel constructed the physical plant, and Enron was charged with managing the project through Enron International. From 1992 to 2001, the construction and operation of the plant was mired in controversies related to corruption in Enron and at the highest political levels in India and the United States (Clinton administration and Bush administration).[2] In 2001, the power plant ran into trouble due to Enron scandal leading to the bankruptcy of Enron.[3] In 2005, it was taken over and revived by converting it into the RGPPL (Ratnagiri Gas and Power Private Limited), a company owned by the Government of India.[4] The infrastruct ...more...

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Electrical wiring in the United Kingdom

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Electrical wiring in the United Kingdom

Electrical wiring in the United Kingdom is commonly understood to be an electrical installation for operation by end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as marinas or caravan parks.[1] It does not normally cover the transmission of electrical power to them. Installations are distinguished by a number of criteria, such as voltage (high, low, extra low), phase (single or 3 phase), nature of electrical signal (power, data), type and design of cable (conductors and insulators used, cable design, solid/fixed or stranded/flexible, intended use, protective materials), circuit design (ring, radial), and so on. Electrical wiring is ultimately regulated to ensure safety of operation, by such as the Building Regulations, currently legislated as the Building Regulations 2010, which lists "controlled services" such as electric wiring that must follow specific directions and standards, and the Electricity at Work Regulations 1989. The d ...more...

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Phase-shift keying

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Phase-shift keying

Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal – such a system is termed coherent (and referred to as ...more...

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Auxiliary power unit

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Auxiliary power unit

A Honeywell GTCP36 APU mounted under the tail of a business jet The APU exhaust at the tail end of an Airbus A380 An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115 V alternating current (AC) at 400 Hz (rather than 50/60 Hz in mains supply), to run the electrical systems of the aircraft; others can produce 28 V direct current (DC).[1] APUs can provide power through single- or three-phase systems. Transport aircraft Function APIC APS3200 APU for Airbus A320 family. The primary purpose of an aircraft APU is to provide power to start the main engines. Turbine engines must be accelerated to a high rotational speed to provide sufficient air compression for self-sustaining operation. Smaller jet engines are usually started by an electric motor, while larger engines are usually started by an air turbine motor. Befor ...more...

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Earthing system

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Earthing system

In an electrical installation an earthing system or grounding system connects specific parts of that installation with the Earth's conductive surface for safety and functional purposes. The point of reference is the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary considerably among countries, though many follow the recommendations of the International Electrotechnical Commission. Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants. In addition to electric power systems, other systems may require grounding for safety or function. Tall structures may have lightning rods as part of a system to protect them from lightning strikes. Telegraph lines may use the Earth as one conductor of a circuit, saving the cost of installation of a return wire over a long circuit. Radio antennas may require particular grounding for ...more...

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Thyristor controlled reactor

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Thyristor controlled reactor

In an electric power transmission system, a thyristor-controlled reactor (TCR) is a reactance connected in series with a bidirectional thyristor valve. The thyristor valve is phase-controlled, which allows the value of delivered reactive power to be adjusted to meet varying system conditions. Thyristor-controlled reactors can be used for limiting voltage rises on lightly loaded transmission lines. Another device which used to be used for this purpose is a magnetically controlled reactor (MCR), a type of magnetic amplifier otherwise known as a transductor. In parallel with series connected reactance and thyristor valve, there may also be a capacitor bank, which may be permanently connected or which may use mechanical or thyristor switching. The combination is called a static VAR compensator. Circuit diagram A thyristor controlled reactor is usually a three-phase assembly, normally connected in a delta arrangement to provide partial cancellation of Harmonics. Often the main TCR reactor is split into two halv ...more...

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Bruce Peebles & Co. Ltd.

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Bruce Peebles & Co. Ltd.

Advert c.1900 Interior of rotating plant works 1956 Tank under construction, for Ratcliffe-on-Soar station 1966 Aerial view of Edinburgh works 1978 Reactor under test 1979 Bruce Peebles & Co. Ltd. was an Edinburgh industrial electrical engineering company. Early history The company was founded as D. Bruce Peebles & Co. by Scottish engineer David Bruce Peebles (1826–1899) in Edinburgh in 1866.[1] The company initially specialised in gas engineering but later expanded to include electrical engineering as well. It continued to trade after Peebles' death and, in 1902, the name was changed to Bruce Peebles & Co. Ltd. The company held the British manufacturing rights for the Cascade converter and a licence to manufacture three-phase electrical equipment designed by Ganz of Budapest.[2] Canadian Electric Traction Company In 1903, Peebles expanded into Canada. Along with other investors, it formed the Canadian Electric Traction Company and supplied the three-phase equipmen ...more...

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Gas turbine

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Gas turbine

Examples of gas turbine configurations: (1) turbojet, (2) turboprop, (3) turboshaft (electric generator), (4) high-bypass turbofan, (5) low-bypass afterburning turbofan A gas turbine, also called a combustion turbine, is a type of continuous combustion, internal combustion engine. There are three main components: An upstream rotating gas compressor; A downstream turbine on the same shaft; A combustion chamber or area, called a combustor, in between 1. and 2. above. A fourth component is often used to increase efficiency (turboprop, turbofan), to convert power into mechanical or electric form (turboshaft, electric generator), or to achieve greater power to mass/volume ratio (afterburner). The basic operation of the gas turbine is a Brayton cycle with air as the working fluid. Fresh atmospheric air flows through the compressor that brings it to higher pressure. Energy is then added by spraying fuel into the air and igniting it so the combustion generates a high-temperature flow. This high-temperature hi ...more...

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Mobile office

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Mobile office

Mobile Office on the Streets of London. A mobile office is an office built within a truck, motorhome, trailer or purpose built shipping container. Most common are towable offices built on an axled iron frame for easy relocation. Mobile field offices are often found on construction sites, or at disaster scenes where a temporary office space is needed. Typically, mobile offices in North America feature a single phase split (240 volt center-tapped) electric service that is connected to a nearby source of power, to run small window-unit air conditioners, and the like. There are many types of companies that sell, lease, rent new and used storage containers, portable buildings or modular buildings. This type of construction shortens the construction period as the building can be built in a factory in as little as six weeks and the site and utility work can be done in conjunction with the construction of the building. The term "mobile office" is also used for the workspace of salespeople or similar, working out of ...more...

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Cavity magnetron

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Cavity magnetron

Magnetron with section removed to exhibit the cavities. The cathode in the center is not visible. The waveguide emitting microwaves is at the left. The magnet producing a field parallel to the long axis of the device is not shown. A similar magnetron with a different section removed. Central cathode is visible; antenna conducting microwaves at the top; magnet is not shown. Obsolete 9 GHz magnetron tube and magnets from a Soviet aircraft radar. The tube is embraced between the poles of two horseshoe-shaped alnico magnets (top, bottom), which create a magnetic field along the axis of the tube. The microwaves are emitted from the waveguide aperture (top) which in use is attached to a waveguide conducting the microwaves to the radar antenna. Modern tubes use rare earth magnets which are much less bulky. The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity re ...more...

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Refractive index

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Refractive index

A ray of light being refracted in a plastic block In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n = c v , {\displaystyle n={\frac {c}{v}},} where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in vacuum than in the water. Refraction of a light ray The refractive index determines how much the path of light is bent, or refracted, when entering a material. This is the first documented use of refractive indices and is described by Snell's law of refraction, n sinθ = n sinθ, where θ and θ are the angles of incidence and refraction, respectively, of a ray crossing the interface between two media with refractive indices n and n. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as ...more...

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Nuclear power

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Nuclear power

The 1200 MWe, Leibstadt fission-electric power station in Switzerland. The boiling water reactor (BWR), located inside the dome capped cylindrical structure, is dwarfed in size by its cooling tower. The station produces a yearly average of 25 million kilowatt-hours per day, sufficient to power a city the size of Boston.[1] The Palo Verde Nuclear Generating Station, the largest in the US with 3 pressurized water reactors (PWRs), is situated in the Arizona desert. It uses sewage from cities as its cooling water in 9 squat mechanical draft cooling towers.[2][3] Its total spent fuel/"waste" inventory produced since 1986, is contained in dry cask storage cylinders located between the artificial body of water and the electrical switchyard. U.S. nuclear powered ships,(top to bottom) cruisers USS Bainbridge, USS Long Beach and USS Enterprise, the first nuclear-powered aircraft carrier. Picture taken in 1964 during a record setting voyage of 26,540 nmi (49,152 km) around the world in 65 days without refueling. ...more...

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Switched-mode power supply

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Switched-mode power supply

Interior view of an ATX SMPS: below A: input EMI filtering and bridge rectifier; B: input filter capacitors; Between B and C: primary side heat sink; C: transformer; Between C and D: secondary side heat sink; D: output filter coil; E: output filter capacitors.   The coil and large yellow capacitor below E are additional input filtering components that are mounted directly on the power input connector and are not part of the main circuit board. An adjustable switched-mode power supply for laboratory use A switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a DC or AC source (often mains power) to DC loads, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continu ...more...

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