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60-966: PMT may refer to: Technology and engineering [ edit ] Pole-mount transformer Padmount transformer Photomultiplier tube , a light detector Medicine [ edit ] Premenstrual tension Pacemaker-mediated tachycardia, caused by artificial pacemaker Pasteurella multocida toxin Political parties [ edit ] Malian Party of Labour (le Parti malien du travail) Mexican Workers' Party (Partido Mexicano de los Trabajadores) Transport [ edit ] PMTair , Cambodian airline, ICAO code Polmont railway station , Scotland, National Rail station code First Potteries Limited, formerly PMT Ltd, UK bus company Pune Municipal Transport, merged into Pune Mahanagar Parivahan Mahamandal Limited , India Other uses [ edit ] Packaging Machinery Technology ,

120-460: A service drop , where wires run from a utility pole or underground power lines to a customer's premises. They are often used for the power supply of facilities outside settlements, such as isolated houses, farmyards, or pumping stations at voltages below 30 kV. Another application is the power supply of the overhead wire of railways electrified with AC. In this case, single-phase distribution transformers are used. The number of customers fed by

180-439: A composite core, for temperature compensation. Saturation flux of about 1 tesla. Good temperature stability. Used in switching power supplies, pulse and flyback transformers, in-line noise filters, swing chokes, and in filters in phase-fired controllers (e.g. dimmers) where low acoustic noise is important. Absence of nickel results in easier processing of the material and its lower cost than both high-flux and MPP. The material

240-433: A concentrated field that is as much as 50,000 times more intense than an air core. Iron is desirable to make magnetic cores, as it can withstand high levels of magnetic field without saturating (up to 2.16 teslas at ambient temperature. ) Annealed iron is used because, unlike "hard" iron, it has low coercivity and so does not remain magnetised when the field is removed, which is often important in applications where

300-456: A concrete pad. Many large buildings have electric service provided at primary distribution voltage. These buildings have customer-owned transformers in the basement for step-down purposes. Distribution transformers are also found in wind farm power collection networks, where they step up power from each wind turbine to connect to a substation that may be several miles (kilometers) distant. Both pole-mounted and pad-mounted transformers convert

360-505: A day (even when they don't carry any load), reducing iron losses is vital in their design. They usually don't operate at full load, so they are designed to have maximum efficiency at lower loads. To have better efficiency, voltage regulation in these transformers should be kept to a minimum. Hence, they are designed to have small leakage reactance . Distribution transformers are classified into different categories based on factors such as: Distribution transformers are normally located at

420-485: A factor of several hundred times what it would be without the core. However, magnetic cores have side effects which must be taken into account. In alternating current (AC) devices they cause energy losses, called core losses , due to hysteresis and eddy currents in applications such as transformers and inductors. "Soft" magnetic materials with low coercivity and hysteresis, such as silicon steel , or ferrite , are usually used in cores. An electric current through

480-408: A few megahertz. However, losses such as proximity effect and dielectric losses are still present. Air cores are also used when field strengths above around 2 Tesla are required as they are not subject to saturation. Most commonly made of ferrite or powdered iron, and used in radios especially for tuning an inductor . The coil is wound around the rod, or a coil form with the rod inside. Moving

540-959: A gap. They contain significant amount of carbon. They behave as much smaller than what their outer size would suggest. The "C-type" particles can be prepared by heating the E-type ones in hydrogen atmosphere at 400 °C for prolonged time, resulting in carbon-free powders. Powdered cores made of hydrogen reduced iron have higher permeability but lower Q than carbonyl iron. They are used mostly for electromagnetic interference filters and low-frequency chokes, mainly in switched-mode power supplies . Hydrogen-reduced iron cores are often called "power cores". An alloy of about 2% molybdenum , 81% nickel , and 17% iron. Very low core loss, low hysteresis and therefore low signal distortion. Very good temperature stability. High cost. Maximum saturation flux of about 0.8 tesla. Used in high-Q filters, resonant circuits, loading coils, transformers, chokes, etc. The material

600-400: A larger coil former and can produce a larger inductor or transformer . If an air gap is required, the centre leg of the "E" is shortened so that the air gap sits in the middle of the coil to minimize fringing and reduce electromagnetic interference . A planar core consists of two flat pieces of magnetic material, one above and one below the coil. It is typically used with a flat coil that

660-418: A magazine Pardon My Take , a comedy sports podcast Parent Management Training PMT Dance Studio , of New York City, US PMT Italia , a paper machinery company Professional Music Technology , a UK musical instrument retailer Program Map Table in an MPEG transport stream Protection motivation theory Precision Mounting Technologies, a mount manufacturing company Topics referred to by

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720-474: A neutral will always be provided as a return path.) Primaries provide power at the standard distribution voltages used in the area; these range from as low as 2.3 kV to about 35 kV depending on local distribution practice and standards, often 11 kV (50 Hz systems) and 13.8 kV (60 Hz systems) are used, but many other voltages are standard. For example, in the United States , the most common voltage

780-482: A plastic or ceramic form in addition to those made of stiff wire that are self-supporting and have air inside them. Air core coils generally have a much lower inductance than similarly sized ferromagnetic core coils, but are used in radio frequency circuits to prevent energy losses called core losses that occur in magnetic cores. The absence of normal core losses permits a higher Q factor , so air core coils are used in high frequency resonant circuits , such as up to

840-435: A pole or may be mounted on cross-arms bolted to the pole. Aerial transformers, larger than around 75 kVA, may be mounted on a platform supported by one or more poles. A three-phase service may use three identical transformers, one per phase. Transformers designed for below-grade installation can be designed for periodic submersion in water. Distribution transformers may include an off-load tap changer, which slightly adjusts

900-487: A single distribution transformer varies depending on the number of customers in an area. Several homes may be fed from a single transformer in urban areas; depending on the mains voltage, rural distribution may require one transformer per customer. A large commercial or industrial complex will have multiple distribution transformers. In urban areas and neighborhoods where primary distribution lines run underground, padmount transformers , and locked metal enclosures are mounted on

960-461: A square closed core, the simplest closed core shape. Windings may be put on one or both legs of the core. E-shaped core are more symmetric solutions to form a closed magnetic system. Most of the time, the electric circuit is wound around the center leg, whose section area is twice that of each individual outer leg. In 3-phase transformer cores, the legs are of equal size, and all three legs are wound. Sheets of suitable iron stamped out in shapes like

1020-407: A suitable organic or inorganic binder, and pressed to desired density. Higher density is achieved with higher pressure and lower amount of binder. Higher density cores have higher permeability, but lower resistance and therefore higher losses due to eddy currents. Finer particles allow operation at higher frequencies, as the eddy currents are mostly restricted to within the individual grains. Coating of

1080-399: A wire wound into a coil creates a magnetic field through the center of the coil, due to Ampere's circuital law . Coils are widely used in electronic components such as electromagnets , inductors , transformers , electric motors and generators . A coil without a magnetic core is called an "air core" coil. Adding a piece of ferromagnetic or ferrimagnetic material in the center of

1140-444: A wound C-shaped core is economical to manufacture. A steel strip is wrapped around a former, pressed into shape, and then cut into two C-shaped halves re-assembled on the copper windings. The primary coils are wound from enamel-coated copper or aluminum wire, and the high-current, low-voltage secondaries are wound using a thick ribbon of aluminum or copper. The windings are insulated with resin-impregnated paper. The entire assembly

1200-413: Is 12.47 kV, with a line-to-ground voltage of 7.2 kV. It has a 7.2 kV phase-to-neutral voltage, exactly 30 times the 240 V on the split-phase secondary side. The high-voltage primary windings are brought out to bushings on the top of the case. The transformer is always connected to the primary distribution lines through protective fuses and disconnect switches . For pole-mounted transformers, this

1260-677: Is always along the same direction, it is an advantage to use grain oriented steel in the preferred orientation. Rotating machines, where the direction of the magnetic field can change, gain no benefit from grain-oriented steel. A family of specialized alloys exists for magnetic core applications. Examples are mu-metal , permalloy , and supermalloy . They can be manufactured as stampings or as long ribbons for tape wound cores. Some alloys, e.g. Sendust , are manufactured as powder and sintered to shape. Many materials require careful heat treatment to reach their magnetic properties, and lose them when subjected to mechanical or thermal abuse. For example,

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1320-443: Is available under names like e.g. Nanoperm, Vitroperm, Hitperm and Finemet. Ferrite ceramics are used for high-frequency applications. The ferrite materials can be engineered with a wide range of parameters. As ceramics, they are essentially insulators, which prevents eddy currents, although losses such as hysteresis losses can still occur. A coil not containing a magnetic core is called an air core . This includes coils wound on

1380-405: Is baked to cure the resin and then submerged in a powder-coated steel tank, which is then filled with transformer oil (or other insulating liquid), which is inert and non-conductive. The transformer oil cools and insulates the windings and protects them from moisture. The tank is temporarily evacuated during manufacture to remove any remaining moisture that would cause arcing and is sealed against

1440-670: Is different from Wikidata All article disambiguation pages All disambiguation pages Pole-mount transformer If mounted on a utility pole , they are called pole-mount transformers . Suppose the distribution lines are located at ground level or underground. In that case, distribution transformers are mounted on concrete pads and locked in steel cases, thus known as distribution tap pad-mount transformers . Distribution transformers typically have ratings less than 200 kVA , although some national standards allow units up to 5000 kVA to be described as distribution transformers. Since distribution transformers are energized 24 hours

1500-559: Is equivalent to a microscopic laminated magnetic circuit (see silicon steel, above), hence reducing the eddy currents , particularly at very high frequencies. Carbonyl iron has lower losses than hydrogen-reduced iron, but also lower permeability. A popular application of carbonyl iron-based magnetic cores is in high-frequency and broadband inductors and transformers , especially higher power ones. Carbonyl iron cores are often called "RF cores". The as-prepared particles, "E-type"and have onion-like skin, with concentric shells separated with

1560-422: Is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites . The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a current-carrying coil of wire around the core. The use of a magnetic core can increase the strength of magnetic field in an electromagnetic coil by

1620-452: Is needed (e.g. pulse and flyback transformers, the high saturation is suitable for unipolar drive), especially where space is constrained. The material is usable up to about 200 kHz. An alloy of 6% aluminium, 9% silicon, and 85% iron. Core losses higher than MPP. Very low magnetostriction , makes low audio noise. Loses inductance with increasing temperature, unlike the other materials; can be exploited by combining with other materials as

1680-430: Is part of a printed circuit board . This design is excellent for mass production and allows a high power , small volume transformer to be constructed for low cost. It is not as ideal as either a pot core or toroidal core but costs less to produce. Usually ferrite or similar. This is used for inductors and transformers . The shape of a pot core is round with an internal hollow that almost completely encloses

1740-427: Is significantly more expensive than hydrogen-reduced iron. Powdered cores made of carbonyl iron , a highly pure iron, have high stability of parameters across a wide range of temperatures and magnetic flux levels, with excellent Q factors between 50 kHz and 200 MHz. Carbonyl iron powders are basically constituted of micrometer-size spheres of iron coated in a thin layer of electrical insulation . This

1800-416: Is the power supply for a hi-fi audio amplifier . The main drawback that limits their use for general purpose applications is the inherent difficulty of winding wire through the center of a torus. Unlike a split core (a core made of two elements, like a pair of E cores), specialized machinery is required for automated winding of a toroidal core. Toroids have less audible noise, such as mains hum, because

1860-440: Is used in transformer cores. Further increase in silicon concentration impairs the steel's mechanical properties, causing difficulties for rolling due to brittleness. Among the two types of silicon steel , grain-oriented (GO) and grain non-oriented (GNO), GO is most desirable for magnetic cores. It is anisotropic , offering better magnetic properties than GNO in one direction. As the magnetic field in inductor and transformer cores

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1920-445: Is usually a ' fused cutout .' An electrical fault melts the fuse, and the device drops open to give a visual indication of trouble. Lineworkers can also manually open it while the line is energized using insulated hot sticks . In some cases, completely self-protected transformers are used, which have a circuit breaker built in, so a fused cutout isn't needed. The low-voltage secondary windings are attached to three or four terminals on

1980-432: Is usually epoxy or other organic resin, susceptible to thermal aging. At higher temperatures, typically above 125 °C, the binder degrades and the core magnetic properties may change. With more heat-resistant binders the cores can be used up to 200 °C. Iron powder cores are most commonly available as toroids. Sometimes as E, EI, and rods or blocks, used primarily in high-power and high-current parts. Carbonyl iron

2040-457: The air from one end of the rod to the other. The air path ensures that the inductor remains linear . In this type of inductor radiation occurs at the end of the rod and electromagnetic interference may be a problem in some circumstances. Like a cylindrical rod but is square, rarely used on its own. This type of core is most likely to be found in car ignition coils. U and C -shaped cores are used with I or another C or U core to make

2100-401: The ( sans-serif ) letters "E" and "I", are stacked with the "I" against the open end of the "E" to form a 3-legged structure. Coils can be wound around any leg, but usually the center leg is used. This type of core is frequently used for power transformers, autotransformers, and inductors. Again used for iron cores. Similar to using an "E" and "I" together, a pair of "E" cores will accommodate

2160-484: The United States, distribution transformers are often installed outdoors on wooden poles. In Europe, it is most common to place them in buildings. If the feeding lines are overhead, these look like towers. If all lines running to the transformer are underground, small buildings are used. In rural areas, sometimes distribution transformers are mounted on poles, and the pole is usually made of concrete or iron due to

2220-417: The advantage of a high fire point and are completely biodegradable in the environment. Pole-mounted transformers often include accessories such as surge arresters or protective fuse links. A self-protected transformer consists of an internal fuse and surge arrester; other transformers have these components mounted separately outside the tank. Pole-mounted transformers may have lugs allowing direct mounting to

2280-544: The circumference of the torus. The symmetry of this geometry creates a magnetic field of circular loops inside the core, and the lack of sharp bends will constrain virtually all of the field to the core material. This not only makes a highly efficient transformer , but also reduces the electromagnetic interference radiated by the coil. It is popular for applications where the desirable features are: high specific power per mass and volume , low mains hum , and minimal electromagnetic interference . One such application

2340-585: The coil can increase the magnetic field by hundreds or thousands of times; this is called a magnetic core. The field of the wire penetrates the core material, magnetizing it, so that the strong magnetic field of the core adds to the field created by the wire. The amount that the magnetic field is increased by the core depends on the magnetic permeability of the core material. Because side effects such as eddy currents and hysteresis can cause frequency-dependent energy losses, different core materials are used for coils used at different frequencies . In some cases

2400-410: The coil. Usually a pot core is made in two halves which fit together around a coil former ( bobbin ). This design of core has a shielding effect, preventing radiation and reducing electromagnetic interference . This design is based on a toroid (the same shape as a doughnut ). The coil is wound through the hole in the torus and around the outside. An ideal coil is distributed evenly all around

2460-459: The core bigger; it is advantageous where cost is more important than mass and size. Saturation flux of about 1 to 1.5 tesla. Relatively high hysteresis and eddy current loss, operation limited to lower frequencies (approx. below 100 kHz). Used in energy storage inductors, DC output chokes, differential mode chokes, triac regulator chokes, chokes for power factor correction, resonant inductors, and pulse and flyback transformers. The binder used

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2520-490: The core, an economically important cause of power loss in utility grids. Two effects cause core losses: hysteresis loss in the steel and eddy currents . Silicon steel has low hysteresis loss , and the laminated construction prevents eddy currents from flowing in the core, which dissipates power in the resistance of the steel. The efficiency of typical distribution transformers is between about 98 and 99 percent. Where large numbers of transformers are made to standard designs,

2580-405: The current, breaking a large core into narrow laminations reduces the power losses drastically. From this, it can be seen that the thinner the laminations, the lower the eddy current losses. A small addition of silicon to iron (around 3%) results in a dramatic increase of the resistivity of the metal, up to four times higher. The higher resistivity reduces the eddy currents, so silicon steel

2640-412: The lines of flux. The layers of insulation serve as a barrier to eddy currents, so eddy currents can only flow in narrow loops within the thickness of each single lamination. Since the current in an eddy current loop is proportional to the area of the loop, this prevents most of the current from flowing, reducing eddy currents to a very small level. Since power dissipated is proportional to the square of

2700-444: The losses are undesirable and with very strong fields saturation can be a problem, and an 'air core' is used. A former may still be used; a piece of material, such as plastic or a composite, that may not have any significant magnetic permeability but which simply holds the coils of wires in place. "Soft" ( annealed ) iron is used in magnetic assemblies, direct current (DC) electromagnets and in some electric motors; and it can create

2760-410: The magnetic field is required to be repeatedly switched. Due to the electrical conductivity of the metal, when a solid one-piece metal core is used in alternating current (AC) applications such as transformers and inductors, the changing magnetic field induces large eddy currents circulating within it, closed loops of electric current in planes perpendicular to the field. The current flowing through

2820-455: The magnetic forces do not exert bending moment on the core. The core is only in compression or tension, and the circular shape is more stable mechanically. The ring is essentially identical in shape and performance to the toroid, except that inductors commonly pass only through the center of the core, without wrapping around the core multiple times. The ring core may also be composed of two separate C-shaped hemispheres secured together within

2880-573: The overhead or underground distribution lines' high 'primary' voltage to the lower 'secondary' or 'utilization' voltage inside the building. The primary distribution wires use the three-phase system. Main distribution lines always have three 'hot' wires plus an optional neutral. In the North American system, where single-phase transformers connect to only one phase wire, smaller 'lateral' lines branching off on side roads may include only one or two 'hot' phase wires. (When only one phase wire exists,

2940-462: The particles with an insulating layer, or their separation with a thin layer of a binder, lowers the eddy current losses. Presence of larger particles can degrade high-frequency performance. Permeability is influenced by the spacing between the grains, which form distributed air gap; the less gap, the higher permeability and the less-soft saturation. Due to large difference of densities, even a small amount of binder, weight-wise, can significantly increase

3000-869: The permeability of mu-metal increases about 40 times after annealing in hydrogen atmosphere in a magnetic field; subsequent sharper bends disrupt its grain alignment, leading to localized loss of permeability; this can be regained by repeating the annealing step. Amorphous metal is a variety of alloys (e.g. Metglas ) that are non-crystalline or glassy. These are being used to create high-efficiency transformers. The materials can be highly responsive to magnetic fields for low hysteresis losses, and they can also have lower conductivity to reduce eddy current losses. Power utilities are currently making widespread use of these transformers for new installations. High mechanical strength and corrosion resistance are also common properties of metallic glasses which are positive for this application. Powder cores consist of metal grains mixed with

3060-562: The ratio between primary and secondary voltage to bring the customer's voltage within the desired range on long or heavily loaded lines. Pad-mounted transformers have secure locked, bolted' and grounded metal enclosures to discourage unauthorized access to live internal parts. The enclosure may also include fuses, isolating switches, load-break bushings, and other accessories as described in technical standards. Pad-mounted transformers for distribution systems typically range from around 100 to 2000 kVA, although some larger units are also used. In

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3120-586: The resistance of the metal heats it by Joule heating , causing significant power losses. Therefore, solid iron cores are not used in transformers or inductors, they are replaced by laminated or powdered iron cores, or nonconductive cores like ferrite . In order to reduce the eddy current losses mentioned above, most low frequency power transformers and inductors use laminated cores, made of stacks of thin sheets of silicon steel : Laminated magnetic cores are made of stacks of thin iron sheets coated with an insulating layer, lying as much as possible parallel with

3180-422: The rod in or out of the coil changes the flux through the coil, and can be used to adjust the inductance . Often the rod is threaded to allow adjustment with a screwdriver. In radio circuits, a blob of wax or resin is used once the inductor has been tuned to prevent the core from moving. The presence of the high permeability core increases the inductance , but the magnetic field lines must still pass through

3240-403: The same term [REDACTED] This disambiguation page lists articles associated with the title PMT . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=PMT&oldid=1238017358 " Category : Disambiguation pages Hidden categories: Short description

3300-405: The transformer's side. Distribution transformers consist of a magnetic core made from laminations of sheet silicon steel ( transformer steel ) stacked and either glued together with resin or banded together with steel straps, with the primary and secondary wire windings wrapped around them. This core construction is designed to reduce core losses and dissipation of magnetic energy as heat in

3360-436: The volume and therefore intergrain spacing. Lower permeability materials are better suited for higher frequencies, due to balancing of core and winding losses. The surface of the particles is often oxidized and coated with a phosphate layer, to provide them with mutual electrical insulation. Powdered iron is the cheapest material. It has higher core loss than the more advanced alloys, but this can be compensated for by making

3420-448: The weather with a gasket at the top. Formerly, distribution transformers for indoor use would be filled with a polychlorinated biphenyl (PCB) liquid. Because these chemicals persist in the environment and adversely affect on animals, they have been banned. Other fire-resistant liquids such as silicones are used where a liquid-filled transformer must be used indoors. Certain vegetable oils have been applied as transformer oil; these have

3480-414: The weight of the transformer. Magnetic core#Core loss A magnetic core is a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets , transformers , electric motors , generators , inductors , loudspeakers , magnetic recording heads , and magnetic assemblies. It

3540-654: Was first introduced in 1940, used in loading coils to compensate capacitance in long telephone lines. It is usable up to about 200 kHz to 1 MHz, depending on vendor. It is still used in above-ground telephone lines, due to its temperature stability. Underground lines, where temperature is more stable, tend to use ferrite cores due to their lower cost. An alloy of about 50–50% of nickel and iron. High energy storage, saturation flux density of about 1.5 tesla. Residual flux density near zero. Used in applications with high DC current bias (line noise filters, or inductors in switching regulators) or where low residual flux density

3600-480: Was invented in Japan in 1936. It is usable up to about 500 kHz to 1 MHz, depending on vendor. A nanocrystalline alloy of a standard iron-boron-silicon alloy, with addition of smaller amounts of copper and niobium . The grain size of the powder reaches down to 10–100 nanometers. The material has very good performance at lower frequencies. It is used in chokes for inverters and in high power applications. It

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