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 causing low power loss per cycle, low core loss, and permeability.
Electrical steel is normally manufactured in cold-rolled strips below 2 mm thick. These strips are cut to contour around make laminations which can be stacked together to produce the laminated cores of transformers, and the stator and rotor of electric motors. Laminations can be cut for their finished shape by a punch and die or, in smaller quantities, may be cut by a laser, or by Core cutting machine.
Silicon significantly increases the electrical resistivity from the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material, particularly if rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen needs to be kept low, because they elements indicate the presence of carbides, sulfides, oxides and nitrides. These compounds, even during particles as small as one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The presence 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 contributing to a rise in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level might be reduced by annealing the steel inside a decarburizing atmosphere, like hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually has a silicon degree of 2 to 3.5% and has similar magnetic properties in every directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually features a silicon measure of 3% (Si:11Fe). It is actually processed in such a manner that the optimal properties are created in the rolling direction, as a result of tight control (proposed by Norman P. Goss) in the crystal orientation in accordance with the sheet. The magnetic flux density is increased by 30% inside the coil rolling direction, although its magnetic saturation is decreased by 5%. It is actually used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is often supplied by the producing mills in coil form and should be cut into “laminations”, that are then used to form a transformer core, which can be an important part of any transformer. Grain-oriented steel can be used in large power and distribution transformers as well as in certain audio output transformers.
CRNGO is less expensive than transformer core cutting machine. It is used when expense is more important than efficiency as well as for applications where direction of magnetic flux is not really constant, as in electric motors and generators with moving parts. You can use it when there is insufficient space to orient components to leverage the directional properties of grain-oriented electrical steel.
This material can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price of about one megakelvin per second, so quickly that crystals tend not to form. Amorphous steel has limitations to foils of about 50 µm thickness. It offers poorer mechanical properties and also as of 2010 it costs about twice as much as conventional steel, making it cost-effective only for some distribution-type transformers.Transformers with amorphous steel cores might have core losses of a single-third that from conventional electrical steels.
Electrical steel is generally coated to increase electrical resistance between laminations, reducing eddy currents, to provide resistance to corrosion or rust, and to serve as a lubricant during die cutting. There are numerous coatings, organic and inorganic, and also the coating used depends upon the application of the steel. The sort of coating selected depends on the heat therapy for the laminations, whether or not the finished lamination will be immersed in oil, and also the working temperature in the finished apparatus. Very early practice would be to insulate each lamination with a layer of paper or even a varnish coating, but this reduced the stacking factor of the core and limited the highest temperature from the core.
The magnetic properties of electrical steel are determined by heat treatment, as improving the average crystal size decreases the hysteresis loss. Hysteresis loss depends on a regular test and, for common grades of electrical steel, may range 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 could be delivered inside a semi-processed state to ensure, after punching the last shape, one final heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is usually delivered with the insulating coating, full heat treatment, and defined magnetic properties, for dexupky53 where punching will not significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or even rough handling can adversely affect electrical steel’s magnetic properties and could also increase noise as a result of 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 was greater than twice the price by weight.
How big magnetic domains in Silicon steel cut to length could be reduced by scribing the top of the sheet with a laser, or mechanically. This greatly decreases the hysteresis losses from the assembled core.