Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to produce specific magnetic properties: small hysteresis area causing low power loss per cycle, low core loss, and permeability.
Electrical steel is generally produced in cold-rolled strips less than 2 mm thick. These strips are cut to shape to make laminations which can be stacked together to form the laminated cores of transformers, along with the stator and rotor of electric motors. Laminations can be cut to their finished shape from a punch and die or, in smaller quantities, can be cut by way of a laser, or by Core cutting machine.
Silicon significantly boosts 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 of the material, especially when rolling it. When alloying, the concentration levels of carbon, sulfur, oxygen and nitrogen must be kept low, because these 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 while also decreasing magnetic permeability. The presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging whenever it slowly leaves the solid solution and precipitates as carbides, thus leading 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 within a decarburizing atmosphere, for example hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually includes a silicon measure of 2 to 3.5% and it has similar magnetic properties in all of the directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually includes a silicon level of 3% (Si:11Fe). It is actually processed in such a way how the optimal properties are created in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% inside the coil rolling direction, although its magnetic saturation is decreased by 5%. It can be employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is usually provided by the producing mills in coil form and has to be cut into “laminations”, that happen to be then used to form a transformer core, which can be a fundamental element of any transformer. Grain-oriented steel can be used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is less expensive than core cutting machine. It really is used when cost is more valuable than efficiency and for applications in which the direction of magnetic flux is not really constant, like 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 is 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 will not form. Amorphous steel is limited to foils of about 50 µm thickness. They have poorer mechanical properties so when of 2010 it costs about twice as much as conventional steel, so that it is cost-effective just for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of a single-third that from conventional electrical steels.
Electrical steel is usually coated to increase electrical resistance between laminations, reducing eddy currents, to supply resistance to corrosion or rust, as well as behave as a lubricant during die cutting. There are several coatings, organic and inorganic, and also the coating used depends upon the use of the steel. The sort of coating selected is determined by the warmth management of the laminations, whether the finished lamination will likely be immersed in oil, as well as the working temperature of the finished apparatus. Very early practice was to insulate each lamination with a layer of paper or perhaps a varnish coating, but this reduced the stacking factor from the core and limited the maximum temperature of your core.
The magnetic properties of electrical steel are influenced by heat treatment, as boosting the average crystal size decreases the hysteresis loss. Hysteresis loss is dependent upon an ordinary test and, for common grades of electrical steel, may range between 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 might be delivered in the semi-processed state to ensure, after punching the last shape, a final heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is usually delivered with an 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 perhaps rough handling can adversely affect electrical steel’s magnetic properties and might 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 had been over twice the cost by weight.
How big magnetic domains in crgo cutting machine can be reduced by scribing the surface of the sheet by using a laser, or mechanically. This greatly decreases the hysteresis losses within the assembled core.