Magnetic wire or enamel wire are copper or aluminum wire coated with a very thin insulating layer. It is used in the construction of transformers, inductors, motors, speakers, hard disk head actuators, electromagnets, and other applications requiring strict isolated wire reels.
The wire itself is most often completely annealed, electrolyte-purified copper. An aluminum magnetic wire is sometimes used for large transformers and motors. This isolation is usually made of a hard polymeric film material rather than enamel, as the name suggests.
Video Magnet wire
Construction
Conductor
The most suitable material for magnetic wire applications is pure metal without metals, especially copper. When factors such as chemical, physical, and mechanical property requirements are considered, copper is considered the first choice conductor for magnetic wire.
Most often, the magnetic wire consists of completely annealed copper, fine electrolyte to allow for closer winding when creating electromagnetic coils. High purity oxygen-free copper levels are used for high temperature applications in reducing the atmosphere or in motors or generators cooled by hydrogen gas.
An aluminum magnetic wire is sometimes used as an alternative to large transformers and motors. Due to its lower electrical conductivity, the aluminum wire requires cross-sectional area 1.6 times larger than the copper wire to achieve comparable DC resistance.
Maps Magnet wire
Isolation
Although described as "enameled", enamel wire is not, in fact, coated with enamel paint or with vitreous enamel made from a fused glass powder. Modern magnetic wire typically uses one to four layers (in the case of quad-type wire films) of polymer film insulation, often of two different compositions, to provide a hard and sustainable insulating layer. The use of magnetic wire insulation film (in order to increase the temperature range) of formal polyvinyl (Formvar), polyurethane, polyamide, polyester, polyester-polyimide, polyamides (or amide-imides), and polymide. The insulated polymide magnetic wire is capable of operating up to 250 ° C. Insulation of square or rectangular magnetic wire is often augmented by wrapping it with high-temperature polymide or fiberglass tape, and the rolls that are resolved are often vacuum impregnated with insulating varnish to enhance the insulation strength and long term reliability the length of the winding.
The standalone coil is wrapped in a coated wire of at least two layers, the outermost is a thermoplastic that binds together when heated.
Other types of insulation such as fiberglass yarn with varnish, aramid paper, kraft paper, mica, and polyester film are also widely used worldwide for various applications such as transformers and reactors. In the audio sector, wires of silver construction, and various other insulators, such as cotton (sometimes absorbed with some type of lump/thickener substance, such as beeswax) and polytetrafluoroethylene (Teflon) can be found. Older insulation materials include cotton, paper, or silk, but these are only useful for low temperature applications (up to 105 ° C).
For ease of manufacturing, some low temperature magnetic wires have insulation that can be released by heat soldering. This means that the electrical connection at the end can be done without removing the insulation first.
Section
Smaller diameter wire magnets usually have a rounded cross section. This kind of wire is used for things like electric guitar pickups. The thick magnetic wire is often square, rectangular or hexagonal (with rounded corners) in transverse sections, packing is more efficient and has greater structural stability and thermal conductivity at adjacent turns.
Classification
Like other wires, magnetic wire is classified in diameter (AWG, SWG or millimeter number) or area (square millimeter), temperature class, and insulation class.
The translucent voltage depends on the thickness of the cover, which can be of 3 types: Grade 1, Grade 2, and Grade 3. The higher level has thicker insulation and thus higher breakdown voltage.
The temperature class indicates the temperature of the wire where it has a service life of 20,000 hours. At lower temperatures, the cable life is longer (about 2 for every 10 ° C lower temperatures). The general temperature class is 105 Ã, Â ° C, 130 Ã, Â ° C, 155 Ã, Â ° C, 180 Ã, Â ° C and 220 Ã, Â ° C.
Current density
In practice, the maximum current density may vary from 2.5 A/mm 2 to wires isolated from free air to 6 A/mm 2 for free-air wires. If the wire carries high frequency currents (above 10 kHz) the effect of the skin can affect the distribution of currents in all parts by centralizing the current on the surface of the conductor.
If active cooling is provided by air or water circulation, much higher current densities can be achieved - in proportion to the cooling effectiveness.
The aluminum wire must have 1.6 times the cross-sectional area as a copper wire to achieve a comparable DC resistance. Because of this, copper magnetic wire contributes to improving energy efficiency in equipment such as electric motors.
Apps
The magnetic wire is used in electric motor windings, transformers, inductors, generators, headphones, loudspeaker coils, hard drive head positioners, electromagnets, and other devices.
In the electric motor
The electric motor converts electrical energy into mechanical motion, usually through the interaction of the magnetic field and the current carrying conductor. Electric motors are found in a variety of diverse applications, such as fans, blowers, pumps, engines, household appliances, electrical appliances, and disk drives. Extremely large electric motors with ratings in thousands of kilowatts are used in applications such as large ship propulsion. The smallest motor moves the clock on an electric watch.
The electric motor contains a coil to produce the required magnetic field. For given motor frame sizes, high conductivity materials reduce energy loss due to coil resistance. Poor conductors generate more waste heat when transferring electrical energy to kinetic energy.
Due to its high electrical conductivity, copper is commonly used in coil rolls, bearings, collectors, brushes, and motor connectors, including high-quality motors. Greater copper conductivity than other materials increases the electrical energy efficiency of the motor. For example, in order to reduce the load loss on induction motor of continuous use over 1 horsepower, manufacturers always use copper as a regulating material in rolls. Aluminum is an alternative material in smaller horsepower motors, especially when the motor is not used continuously.
One element of premium motor design is the reduction of heat loss due to the electrical resistance of the conductor. To improve the electrical energy efficiency of the induction-type motor, the load loss can be reduced by increasing the cross section of the copper coil. High-efficiency motors typically have 20% more copper in stator windings than their standard counterparts.
Initial developments in motor efficiency were focused on reducing electrical losses by increasing the weight of the stator windings. This makes sense because electrical losses typically cause more than half of all energy losses, and stator losses account for about two-thirds of electrical losses.
Nevertheless, there is a disadvantage in increasing the electric efficiency of the motor through larger rolls. This increases the size and cost of the motor, which may be undesirable in applications such as equipment and in cars.
In transformers
The transformer is a device that transfers electrical energy from one circuit to another through its coil (coil). The properties required for motor windings are similar to those required for transformers, but with additional requirements to withstand mechanical vibrations and centrifugal forces at operating temperatures.
The transformer windings are usually made of copper but aluminum is a suitable competitor where weight and cost first are the deciding factors.
In North America, aluminum is the ultimate choice of winding material for low voltage transformers, a dry type greater than 15 kilovolt-amperes (kVA). In most other regions of the world, copper is the main winding material. Purchase decisions are generally a function of valuation of losses expressed in currencies per kilowatt.
The copper used for the manufacture of transformer reels is in the form of wires for small products and strips for larger appliances. For small products, the wire must be strong enough to be unbroken, but flexible enough to produce a closed roll. The strip product must have good surface quality so that the insulating enamel is not damaged under the voltage. Good ductility is essential for strips to be shaped and packaged while good strength is required to withstand the high electro-mechanical pressure formed under occasional short-circuit conditions. The copper winding wires in the transformer are compatible with all modern insulation materials, such as lacquers and enamels. Lacquer allows close-spacing coils to provide the best efficiency in rolls.
The reason for the main technique for selecting copper reels over aluminum is the consideration of space. This is because copper-wound transformers can be made smaller than aluminum transformers. To obtain the same rank in aluminum transformers, 66% larger cross-section area is required than for copper conductors. However, the use of larger conductors yields the strength of the aluminum coil almost equal to the copper coil.
Connectivity is another important benefit of the copper-wound transformer. Cleaning and brushing with high quality compound to prevent oxidation is not needed with copper.
In generator
The trend in modern generators is to operate at higher temperatures and higher electrical conductivity with oxygen-free copper for field bars and magnetic wire in place of previously used deoxidized copper.
References
Source of the article : Wikipedia
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