Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) can be a special steel tailored to generate specific magnetic properties: small hysteresis area contributing to low power loss per cycle, low core loss, and permeability.
Electrical steel is generally made in cold-rolled strips lower than 2 mm thick. These strips are cut to contour around make laminations that happen to be stacked together to make the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations may be cut on their finished shape by a punch and die or, in smaller quantities, may be cut by way of 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 of your material, specially when rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen has to be kept low, because these elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even 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 if it slowly leaves the solid solution and precipitates as carbides, thus leading to a rise in power loss with time. Because of this, the carbon level is kept to .005% or lower. The carbon level may be reduced by annealing the steel in the decarburizing atmosphere, including hydrogen.
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually includes a silicon measure of 2 to 3.5% and contains similar magnetic properties in every 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 way that the optimal properties are created in the rolling direction, caused by a tight control (proposed by Norman P. Goss) of your crystal orientation in accordance with 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 employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is normally abbreviated to CRGO.
CRGO is often supplied by the producing mills in coil form and should be cut into “laminations”, that are then used produce 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 cheaper than cut to length. It is used when pricing is more important than efficiency and also for applications in which the direction of magnetic flux is not really constant, like in electric motors and generators with moving parts. It can be used should there be insufficient space to orient components to take advantage of the directional properties of grain-oriented electrical steel.
This material is actually a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal at a rate of about one megakelvin per second, so quickly that crystals do not form. Amorphous steel has limitations to foils around 50 µm thickness. It has poorer mechanical properties so that as of 2010 it costs about double the amount as conventional steel, making it inexpensive just for some distribution-type transformers.Transformers with amorphous steel cores may have core losses of merely one-third that 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 also to act as a lubricant during die cutting. There are many coatings, organic and inorganic, and the coating used depends upon the application of the steel. The type of coating selected is dependent upon the warmth treatment of the laminations, regardless of if the finished lamination is going to be immersed in oil, as well as the working temperature of the finished apparatus. Very early practice would be to insulate each lamination having a layer of paper or possibly a varnish coating, but this reduced the stacking factor in the core and limited the utmost temperature from the core.
The magnetic properties of electrical steel are dependent on heat treatment, as improving the average crystal size decreases the hysteresis loss. Hysteresis loss is dependent upon a regular test and, for common grades of electrical steel, may cover anything 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 may be delivered in the semi-processed state so that, after punching the very last shape, one final heat treatment does apply to form the normally required 150-micrometer grain size. Fully processed electrical steel is generally delivered with the 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, as well as rough handling can adversely affect electrical steel’s magnetic properties and may even also increase noise because of magnetostriction.
The magnetic properties of electrical steel are tested using the internationally standard Epstein frame method.
Electrical steel is far more costly than mild steel-in 1981 it was a lot more than twice the price by weight.
The dimensions of magnetic domains in Silicon steel cut to length can be reduced by scribing the top of the sheet having a laser, or mechanically. This greatly cuts down on the hysteresis losses in the assembled core.