Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is a special steel tailored to make specific magnetic properties: small hysteresis area leading to low power loss per cycle, low core loss, and high permeability.
Electrical steel is normally produced in cold-rolled strips under 2 mm thick. These strips are cut to shape to make laminations that happen to be stacked together to form the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations can be cut on their finished shape with a punch and die or, in smaller quantities, could be cut by way of a laser, or by cut to length machine.
Silicon significantly raises the electrical resistivity in the steel, which decreases the induced eddy currents and narrows the hysteresis loop in the material, thus reducing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability from the material, particularly if rolling it. When alloying, the concentration levels of carbon, sulfur, oxygen and nitrogen has to be kept low, because these elements indicate the actual existence of carbides, sulfides, oxides and nitrides. These compounds, even just in particles no more than one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The inclusion of carbon carries 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 causing an increase in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel in the decarburizing atmosphere, for example hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually has a silicon level of 2 to 3.5% and has similar magnetic properties in all of the directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually features a silicon measure of 3% (Si:11Fe). It really is processed in such a manner how the optimal properties are created in the rolling direction, as a result of tight control (proposed by Norman P. Goss) of your crystal orientation relative to the sheet. The magnetic flux density is increased by 30% within the coil rolling direction, although its magnetic saturation is decreased by 5%. It is actually useful for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is normally provided by the producing mills in coil form and should be cut into “laminations”, which can be then used to make a transformer core, which is an integral part of any transformer. Grain-oriented steel is used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is less expensive than core cutting machine. It can be used when pricing is more important than efficiency and also for applications the location where the direction of magnetic flux is just not constant, as with electric motors and generators with moving parts. You can use it should there be insufficient space to orient components to make use of the directional properties of grain-oriented electrical steel.
This product is a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal at a rate of around one megakelvin per second, so quick that crystals do not form. Amorphous steel is limited to foils of about 50 µm thickness. They have poorer mechanical properties and as of 2010 it costs about twice as much as conventional steel, which makes it inexpensive only for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of a single-third that of conventional electrical steels.
Electrical steel is usually coated to improve electrical resistance between laminations, reducing eddy currents, to supply resistance to corrosion or rust, and to work as a lubricant during die cutting. There are numerous coatings, organic and inorganic, and the coating used depends upon the use of the steel. The sort of coating selected is determined by the warmth treatment of the laminations, if the finished lamination will probably be immersed in oil, and the working temperature from the finished apparatus. Very early practice would be to insulate each lamination having a layer of paper or perhaps a varnish coating, but this reduced the stacking factor of the core and limited the maximum temperature from the core.
The magnetic properties of electrical steel are determined by heat treatment, as enhancing the average crystal size decreases the hysteresis loss. Hysteresis loss is determined by a typical test and, for common grades of electrical steel, may vary from a couple of to 10 watts per kilogram (1 to 5 watts per pound) at 60 Hz and 1.5 tesla magnetic field strength.
Electrical steel may be delivered within a semi-processed state to ensure, after punching the final shape, one last heat treatment can be applied to make the normally required 150-micrometer grain size. Fully processed electrical steel is generally delivered with an insulating coating, full heat treatment, and defined magnetic properties, for dexupky53 where punching does not significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or perhaps rough handling can adversely affect electrical steel’s magnetic properties and may even also increase noise due to magnetostriction.
The magnetic properties of electrical steel are tested utilizing the internationally standard Epstein frame method.
Electrical steel is far more costly than mild steel-in 1981 it absolutely was a lot more than twice the cost by weight.
The size of magnetic domains in Transformer core cutting machine can be reduced by scribing the surface of the sheet having a laser, or mechanically. This greatly reduces the hysteresis losses within the assembled core.