Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to make specific magnetic properties: small hysteresis area contributing to low power loss per cycle, low core loss, and permeability.
Electrical steel is usually manufactured in cold-rolled strips under 2 mm thick. These strips are cut to contour around make laminations that are stacked together to create the laminated cores of transformers, and the stator and rotor of electric motors. Laminations might be cut to their finished shape by a punch and die or, in smaller quantities, may be cut from a laser, or by Core cutting machine.
Silicon significantly raises the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus reducing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability in the material, specially when rolling it. When alloying, the concentration levels of carbon, sulfur, oxygen and nitrogen needs to be kept low, because they elements indicate the inclusion of carbides, sulfides, oxides and nitrides. These compounds, even just in particles as small as one micrometer in diameter, increase hysteresis losses as well as decreasing magnetic permeability. The inclusion of carbon carries a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging in the event it slowly leaves the solid solution and precipitates as carbides, thus causing a rise in power loss over time. Because of this, the carbon level is kept to .005% or lower. The carbon level might be reduced by annealing the steel inside a decarburizing atmosphere, including hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually carries a silicon amount of 2 to 3.5% and contains similar magnetic properties in all of the directions, i.e., it can be isotropic. Cold-rolled non-grain-oriented steel is normally abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon level of 3% (Si:11Fe). It can be processed in such a manner that the optimal properties are created in the rolling direction, because of a tight control (proposed by Norman P. Goss) of the 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 can be used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is frequently abbreviated to CRGO.
CRGO is normally provided by the producing mills in coil form and needs to be cut into “laminations”, that happen to be then used to make a transformer core, which is a fundamental part of any transformer. Grain-oriented steel is utilized in large power and distribution transformers and also in certain audio output transformers.
CRNGO is more affordable than cut to length. It can be used when cost is more important than efficiency and then for applications the location where the direction of magnetic flux is not constant, as with electric motors and generators with moving parts. You can use it if you find insufficient space to orient components to benefit from the directional properties of grain-oriented electrical steel.
This product can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price of approximately one megakelvin per second, so fast that crystals will not form. Amorphous steel has limitations to foils of around 50 µm thickness. It provides poorer mechanical properties and as of 2010 it costs about twice as much as conventional steel, which makes it cost-effective just for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of merely one-third those of conventional electrical steels.
Electrical steel is usually coated to increase electrical resistance between laminations, reducing eddy currents, to offer potential to deal with corrosion or rust, and to serve as a lubricant during die cutting. There are many coatings, organic and inorganic, and also the coating used is dependent upon the effective use of the steel. The type of coating selected depends upon the high temperature treatments for the laminations, whether the finished lamination will likely be immersed in oil, and also the working temperature in 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 from the core and limited the maximum temperature in 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 depends on an ordinary test and, for common grades of electrical steel, may vary from about 2 to 10 watts per kilogram (1 to 5 watts per pound) at 60 Hz and 1.5 tesla magnetic field strength.
Electrical steel can be delivered within a semi-processed state to ensure that, after punching the ultimate shape, a final heat treatment does apply to form the normally required 150-micrometer grain size. Fully processed electrical steel is often delivered having an insulating coating, full heat treatment, and defined magnetic properties, for dexupky53 where punching fails to significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or perhaps rough handling can adversely affect electrical steel’s magnetic properties and could also increase noise on account of magnetostriction.
The magnetic properties of electrical steel are tested utilizing the internationally standard Epstein frame method.
Electrical steel is a lot more costly than mild steel-in 1981 it was over twice the charge by weight.
How big magnetic domains in Silicon steel cut to length might be reduced by scribing the surface of the sheet with a laser, or mechanically. This greatly reduces the hysteresis losses within the assembled core.