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Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system Core loss (or iron loss) is a form of Energy loss that occurs in electrical Transformers and other Inductors The loss is due to a variety of In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field.

The material is usually manufactured in the form of cold-rolled strips less than 2 mm thick. Cold rolling is a Metal working process in which metal is deformed by passing it through rollers at a temperature below its Recrystallization temperature These strips are called laminations when stacked together to form a core. A laminate is a material constructed by uniting two or more layers of material together Once assembled, they form the laminated cores of transformers or the stator and rotor parts of electric motors. The magnetic core is a key component in electrical and electromechanical devices such as Electromagnets Transformers and Inductors A magnetic core is a A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors The stator is the stationary part of an Electric generator or Electric motor. The rotor is the non-stationary part of a rotary Electric motor or Alternator, which rotates because the wires and magnetic field of the motor are arranged so An electric motor uses Electrical energy to produce Mechanical energy. Laminations may be cut to their finished shape by a punch and die, or in smaller quantities may be cut by a laser.

Contents

Metallurgy

Electrical steel is an iron alloy which may have from zero to 6. 5% silicon (Si:5Fe). Silicon significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and thus reduces the core loss. An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in Manganese and aluminum can be added up to 0. WikipediaNaming 5%.

Increasing the amount of silicon inhibits eddy currents and narrows the hysteresis loop of the material, thus lowering the core losses. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system Core loss (or iron loss) is a form of Energy loss that occurs in electrical Transformers and other Inductors The loss is due to a variety of However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material, especially when rolling it. When alloying, the concentration levels of carbon, sulfur, oxygen and nitrogen must be kept low, as these elements indicate the presence of carbides, sulfides, oxides and nitrides. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 These compounds, even in particles as small as one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. The presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it slowly leaves the solid solution and precipitates as carbides, thus resulting in an increase in power loss over time. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. For these reasons, the carbon level is kept to 0. 005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, such as hydrogen. Annealing, in Metallurgy and Materials science, is a Heat treatment wherein a material is altered causing changes in its properties such as strength Decarburization is the process opposite to Carburization, namely aimed at decreasing the content of Carbon in Metals (usually Steel) Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1

Grain orientation

There are two main types of electrical steel: grain-oriented and non-oriented.

Grain-oriented electrical steel usually has a silicon level of 3% (Si:11Fe). It is processed in such a way that the optimum properties are developed in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation relative to the sheet. Norman P Goss (born February 04, 1906 - died October 28, 1977) - inventor and researcher from Cleveland, USA. Due to the special orientation, the magnetic flux density is increased by 30% in the coil rolling direction, although its magnetic saturation is decreased by 5%. Magnetic flux, represented by the Greek letter Φ ( Phi) is a measure of quantity of Magnetism, taking into account the strength and the extent of a Magnetic Seen in some Magnetic materials saturation is the state reached when an increase in applied external Magnetizing field H cannot increase the It is used for the cores of high-efficiency transformers, electric motor and generators. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors An electric motor uses Electrical energy to produce Mechanical energy. In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic

Non-oriented electrical steel usually has a silicon level of 2 to 3. 5% and has similar magnetic properties in all directions, which makes it isotropic. Isotropy is uniformity in all directions Precise definitions depend on the subject area It is less expensive and is used in applications where the direction of magnetic flux is changing, such as electric motors and generators. It is also used when efficiency is less important or when there is insufficient space to correctly orient components to take advantage of the anisotropic properties of grain-oriented electrical steel. Anisotropy (pronounced with stress on the third syllable ˌænaɪˈsɒtrəpi is the property of being directionally dependent as opposed to Isotropy, which means homogeneity

Lamination coatings

Electrical steel is usually coated to increase electrical resistance between laminations, to provide resistance to corrosion or rust, and to act as a lubricant during die cutting. Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings Rust is a general term for a series of Iron oxides, usually red oxides formed by the reaction of Iron with Oxygen in the presence of water or air There are various coatings, organic and inorganic, and the coating used depends on the application of the steel. An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Traditionally inorganic compounds are considered to be of mineral not biological origin [1] The type of coating selected depends on the heat treatment of the laminations, whether the finished lamination will be immersed in oil, and the working temperature of the finished apparatus. Former practice was to insulate each lamination with a layer of paper or a varnish coating, but this reduced the stacking factor of the core and limited the maximum temperature of the core. [2]

Magnetic properties

The magnetic properties of electrical steel are dependent on heat treatment, as increasing the average crystal size decreases the hysteresis loss. Second Album by Rock and roll Singer-songwriter near-legend Graham Parker. Hysteresis loss is determined by a standard test and for common grades of electrical steel may range from about 2 to 10 watts per kilogram (1 to 5 watts per pound) at 60 Hz and 1. 5 tesla magnetic field strength. Semi-processed electrical steels are delivered in a state that, after punching the final shape, a final heat treatment develops the desired 150-micrometer grain size. The fully processed steels are usually delivered with insulating coating, full heat treatment, and defined magnetic properties, for applications where the punching operation does not significantly degrade the material properties. An insulator, also called a Dielectric, is a material that resists the flow of Electric current. Excessive bending, incorrect heat treatment, or even rough handling of core steel can adversely effect its magnetic properties and may also increase noise due to magnetostriction [3]

Amorphous steel

For certain transformers, cores made of amorphous steel are used. Magnetostriction is a property of Ferromagnetic materials that causes them to change their shape when subjected to a Magnetic field. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors This material is a metallic glass prepared by pouring molten alloy steel on a rotating cooled wheel, which cools the metal so quickly (a rate of about one million degrees per second) that crystals do not form. An amorphous metal is a Metallic material with a disordered atomic-scale structure The resulting amorphous metal transformers may have losses due to the core material only one-third that of conventional steels. Amorphous Metal Transformer (AMT is a type of Energy efficient transformer found on electric grids However, its high cost (about twice that of conventional steel) and lower mechanical properties make use of amorphous steel economical only for certain distribution-type transformers. [4]

Practical concerns

Core steel is much more costly than the mild steel used for apparatus tanks, generator frames, etc. - in 1981 it was more than twice the cost per unit weight. [5]

The size of magnetic domains in the sheet can be reduced by scribing the surface of the sheet with a laser, or mechanically. This greatly reduces the hysteresis losses in the assembled core. [6]

See also

References

  1. ^ Beatty, Standard Handbook for Electrical Engineers 11th ed. Ferrosilicon, or ferrosilicium, is a Ferroalloy an alloy of Iron and Silicon with between 15 and 90% silicon , pg. 4-111
  2. ^ Les Jump
  3. ^ Les Jump
  4. ^ John Whincup, News Item Globe and Mail March 3rd, Federal Pioneer BAT, March 1983
  5. ^ Les Jump, Transformer Steel and Cores, Federal Pioneer BAT, March 1981
  6. ^ Richard de Lhorbe Steel No Lasers Here, Federal Pioneer BAT, June/July 1981

External links

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