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Encyclopedia > Electric insulator
Conducting copper wire insulated by an outer layer of polyethylene
Conducting copper wire insulated by an outer layer of polyethylene

An insulator is a material or object which contains no free electrons to permit the flow of electricity. When a voltage is placed across an insulator, no charge/current flows. Image File history File linksMetadata Stripped_wire. ... Image File history File linksMetadata Stripped_wire. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Atomic mass 63. ... Lightning strikes during a night-time thunderstorm. ... Electric potential is the potential energy per unit of charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ...

Contents

Explanation

The term electrical insulator has the same meaning as the term dielectric, but the two terms are often used in different contexts. Conductors and semiconductors, which contain movable charges are the opposite of electrical insulators. Very pure semiconductors are insulators at low temperatures unless doped with impurity atoms that release extra charges which can flow in a current. A few materials (such as silicon dioxide) are almost ideal electrical insulators, a property that is invaluable in flash memory technology. Teflon is another almost ideal insulator, making it a valuable material for long term charge storage in electrets. A much larger class of materials, for example rubber-like polymers and most plastics are still "good enough" to insulate electrical wiring and cables even though they may have lower bulk resistivity. These materials can serve as practical and safe insulators for low to moderate voltages (hundreds, or even thousands, of volts). A dielectric, or electrical insulator, is a substance that is highly resistant to electric current. ... In science and engineering, conductors are materials that contain movable charges of electricity. ... A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ... Nonconductors or electrical insulators are materials which lack movable electric charges, and which therefore lack a low-resistance path for charge flow. ... In semiconductor production, doping refers to the process of intentionally introducing impurities into an intrinsic semiconductor in order to change its electrical properties. ... R-phrases R42 R43 R49 S-phrases S22 S36 S37 S45 S53 Flash point non-flammable Supplementary data page Structure and properties n, εr, etc. ... A USB Flash Memory Device. ... Teflon is polytetrafluoroethylene (PTFE), a polymer of fluorinated ethylene. ... Electret (formed of elektr- from electricity and -et from magnet) is material that has been permanently electrically charged (polarised). ... The term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. ... This article refers to metallic wire. ... 6 or 15cm outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. ... Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. ... Josephson junction array chip developed by NIST as a standard volt. ...


Rubber was replaced by polymers in the mid1960s for premimum and heavy duty use.


The main properties of insulation for house wiring is for physical endurance, vs having good electrical properties. Designers and listers, like UL and CSA, are careful to make the physical properties as good as that of the 1930s and 1940 wires and cables, because they have withstood the test of time. Much wiring of the 1940 vintage is still in use as of 2006.


Physics of conduction in solids

Electrical insulation is the absence of electrical conduction. Electronic band theory (a branch of physics) predicts that a charge will flow whenever there are states available into which the electrons in a material can be excited. This allows them to gain energy and thereby move through the conductor (usually a metal). If no such states are available, the material is an insulator. Electrical conduction is the movement of electrically charged particles through matter. ... In solid state physics, the electronic band structure (or simply band structure) of a solid describes ranges of energy that an electron is forbidden or allowed to have. ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms positive ions (cations) and has metallic bonds. ...


Most (though not all) insulators are characterized by having a large band gap. This occurs because the "valence" band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it. There is always some voltage (called, the breakdown voltage) that will give the electrons enough energy to be excited into this band. Once this voltage is exceeded, the material ceases being an insulator, and charge will begin to pass through it. However, dielectric breakdown is usually accompanied by physical or chemical changes that permanently degrade the material's insulating properties. A Mott Insulator is a metal that naturally does not conduct electricity, however under certain conditions the metal can be made to conduct electricity. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ... Breakdown Voltage (Insulator) = The minimum voltage that makes an insulator react as a conductor. ... The term electrical breakdown has several similar but distinctly different meanings. ...


Materials which lack electron conduction must also lack other mobile charges as well. For example, if a liquid or gas contains ions, then the ions can be made to flow as an electric current, and the material is a conductor. Electrolytes and plasmas contain ions and will act as conductors whether or not electron flow is involved. An electrolyte is a substance that dissociates into free ions when dissolved (or molten), to produce an electrically conductive medium. ... A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation A solar coronal mass ejection blasts plasma throughout the solar system. ...


High-voltage insulators

Detail of the insulators (the vertical string of discs) on a 275 kV suspension pylon near Thornbury, South Gloucestershire, England
Detail of the insulators (the vertical string of discs) on a 275 kV suspension pylon near Thornbury, South Gloucestershire, England

High-voltage insulators used for high-voltage power transmission are made from glass, porcelain, or composite polymer materials. Porcelain insulators are made from clay, quartz or alumina and feldspar, and are covered with a smooth glaze to shed dirt. Insulators made from porcelain rich in Alumina are used where high mechanical strength is a criterion. Glass insulators were (and in some places still are) used to suspend electrical power lines. Some insulator manufacturers stopped making glass insulators in the late 1960's, switching to various ceramic and, more recently, composite materials. Detail of the insulators and vibration dampers on an electricity pylon near Thornbury, South Gloucestershire, England. ... Detail of the insulators and vibration dampers on an electricity pylon near Thornbury, South Gloucestershire, England. ... Power line redirects here. ... Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ... It has been suggested that Porcelain tile be merged into this article or section. ... Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct within the finished structure. ... The Gay Head cliffs in Marthas Vineyard are made almost entirely of clay. ... Quartz is one of the most common minerals in the Earths continental crust. ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ...


Recently, some electric utilities have begun converting to composite for some types of insulators which consist of a central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or EPDM. Composite insulators are less costly, lighter weight, and they have excellent hydrophobic capability. This combination makes them ideal for service in polluted areas. However, these materials do not yet have the long-term proven service life of glass and porcelain. Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct within the finished structure. ... Fibre reinforced plastic (FRP) is a composite material comprising a polymer matrix reinforced with fibres usually of glass, carbon, or aramid and is commonly used in aerospace, automotive and marine industries. ... Silicone caulking can be used as a basic sealant against water and air penetration. ... EPDM rubber (ethylene propylene diene monomer rubber) is an elastomer which is characterized by wide range of applications. ...


The first glass insulators used en masse had an unthreaded pinhole. These pieces of glass were positioned on a tapered wooden pin, vertically extending upwards from the pole's crossarm (commonly only two insulators to a pole and maybe one on top of the pole itself). Natural contraction and expansion of the wires tied to these "threadless insulators" resulted in insulators unseating from their pins, requiring manual reseating.


Amongst the first to produce ceramic insulators were companies in the United Kingdom, with Stiff and Doulton using stoneware from the mid 1840s, Joseph Bourne (later renamed Denby) producing them from around 1860 and Bullers from 1868 Utility patent number. 48,906 was granted to Louis A. Cauvet on July 25, 1865 for a process to produce insulators with a threaded pinhole. To this day, pin-type insulators still have threaded pinholes. A Staffordshire stoneware plate from the 1850s with transferred copper print - (From the home of JL Runeberg) Stoneware is a category of clay and a type of pottery distinguished primarily by its firing and maturation temperature (from about 1200°C to 1315 °C). ... A patent is a set of exclusive rights granted by a state to a patentee (the inventor or assignee) for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which... July 25 is the 206th day (207th in leap years) of the year in the Gregorian calendar, with 159 days remaining. ... 1865 (MDCCCLXV) is a common year starting on Sunday. ...


The invention of suspension-type insulators made high-voltage power transmission possible. Pin-type insulators were unsatisfactory over about 40,000 volts.


Insulation of mast radiators

In most cases a mast radiator construction requires an insulating mounting, therefore insulators of steatite are used. They have to withstand not only the voltage of the mast radiator to ground, which can reach values up to 400 kV at some mast radiators, but also the weight of the mast construction and dynamic forces. Arcing horns and lightning arresters are necessary because lightning strikes in the mast are common. A typical mast radiator Base feed: mast is fed from Aerial Tuning Unit on right via conductor to top of brown ceramic insulator. ... An Egyptian carved and glazed steatite scarab amulet. ...


At guyed mast radiators, it is often necessary to use insulators in the guy (if they are not grounded via a coil at the anchor bases), in order to prevent undesired electrical resonances of the guys. These insulators also have to be equipped with overvoltage protection equipment. For the dimensions of the guy insulation, static charges on guys have to be considered, at high masts these can be much higher than the voltage caused by the transmitter requiring guys divided by insulators in multiple sections on the highest masts. In this case, guys which are grounded at the anchor basements via a coil - or if possible, directly - are the better choice.


Insulation in electrical apparatus

The most important insulation material is air, but a wide variety of solid insulators are used in electrical apparatus. In transformers, generators, and electric motors with a maximum of 2500 volts to ground between turns, the insulation on the coil wires is a thin coating of varnish so as to get the maximum number of turns in each slot space. Large power transformer windings are still mostly insulated with paper, wood, and silicone oil; although these materials have been used for more than 100 years, they still provide a good balance of economy and adequate performance. Bus bars and circuit breakers in switchgear may be insulated with glass-reinforced plastic insulation, treated to have low flame spread and to prevent tracking of current across the material. In old apparatus made up to the early 1970's, boards made of compressed asbestos may be used; while this is an adequate insulator at power frequencies, handling or repairs to asbestos material will release dangerous fibers into the air and must be carried out with a high level of precautions. Live-front switchboards up to the early part of the 20th century were made of slate. Electrical power cables may be insulated with polyethylene, crosslinked polyethylene, PVC, rubber-like polymers, oil impregnated paper, Teflon, silicone, fluorinate dethylene propylene, modified ethylene terafluor-ethylene, or even compressed inorganic powder, depending on the application. Three-phase pole-mounted step-down transformer. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into kinetic energy. ... Fibrous asbestos on muscovite Asbestos Asbestos Asbestos (a misapplication of Latin: asbestos quicklime from Greek : a, not and sbestos, extinguishable) describes any of a group of minerals that can be fibrous, many of which are metamorphic and are hydrous magnesium silicates. ... A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. ... This article or section does not cite its references or sources. ... Polyvinyl chloride Polyvinyl chloride, (IUPAC über Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. ... Teflon is polytetrafluoroethylene (PTFE), a polymer of fluorinated ethylene. ... PVC-sheathed MICC cable. ...


Insulation materials that perform well at power and low frequencies may be unsatisfactory at radio frequency, due to excess dielectric dissipation.


Low-voltage insulating materials

Flexible insulating materials such as PVC (polyvinyl chloride) are used to insulate the circuit and prevent human contact with a 'live' wire -- one having voltage of 600 volts or less. Alternative materials are likely to become increasingly used due to EU safety and environmental legislation making PVC less economic. Polyvinyl chloride Polyvinyl chloride, (IUPAC über Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. ...


Wires and cables operating at less than 50 volts are "covered" with insulation like materials which are NOT voltage rated: eg: telephone cables, door bell wire, the cables to welding electrodes, the service drop cable from the power company to a building. The main criteria is that of mechanical strength, not electrical.


Class 1 and Class 2 insulation

Class 1 insulation requires that the metal body of the apparatus/equipment is solidly connected via a "grounding" wire which is earthed at the main Service Panel; but only basic insulation of the conductors is needed. This equipment is easily identified by a round pin for the grounding connection.


Class 2 insulation means that the equipment/apparatus is double insulated and is used on some appliances such as electric shavers, hair dryers and portable power tools. Double insulation requires that the devices have basic and supplementary insulation, each of which is sufficient to prevent electric shock. All internal electrically energized components are totally enclosed within insulated packaging which prevents any contact with "live" parts. They can be recognised because their leads have two pins, or on 3 pin plugs the third (earth) pin is made of plastic rather than metal. In the EU, double insulated appliances all are marked with a symbol of 2 squares, one inside the other. A pair of angles are supplementary if their respective measures sum to 180 degrees. ... Sign warning of possible electric shock hazard An electric shock may occur upon contact with electricity. ... Ground symbols The term ground or earth usually means a common return path in electrical circuits. ...


Collecting insulators

In the late 1960s and early 1970s, glass insulators were being removed from telephone poles as advances in technology made them obsolete. As linemen were taking down the old lines, they started to notice the multitude of bright colors, company names, variety of shapes, and important historical position held by insulators in the expansion of communication technology. Presently the insulator collecting hobby has thousands of people around the world. A number of websites exist that hold these items as the primary focus, and eBay even has a separate category for insulators. One private website is the Glass Insulators Reference Site.


Collectors have defined a classification system for some of the different styles of small insulators, a price guide (last published in 2003). This is specific to collectors; it is unrecognised, irrelevant and largely unknown by manufacturers. One US-based collectors organization is the (National Insulator Association). The main magazine in the hobby is a monthly publication, Crown Jewels of the Wire, which has been published since 1969.


See also

Arcing horns are a pair of conductors (usually steel) used to protect insulators or insulator strings from damage due to system overvoltage conditions. ... A pylon is a tall steel lattice structure used to support overhead electricity conductors for power transmission. ... A 115 kV to 41. ... A typical mast radiator Base feed: mast is fed from Aerial Tuning Unit on right via conductor to top of brown ceramic insulator. ... A Mott Insulator is a metal that naturally does not conduct electricity, however under certain conditions the metal can be made to conduct electricity. ... Emily Davenport. ...

References

Bullers of Milton Sue Taylor Churnet Valley Books. 2003 ISBN 1-897949-96-0


External links

  • Glass Insulators Reference Site
  • National Insulator Association
  • Specialising in UK telegraph insulators with a railway bias
  • One person's obsession with telephone pole insulators
  • Transcontinental Telegraph Insulators, 1867
  • www.insulatorscanada.com

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