Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is a special steel tailored to generate specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and permeability.
Electrical steel is usually manufactured 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 create the laminated cores of transformers, along with the stator and rotor of electric motors. Laminations might be cut with their finished shape by a punch and die or, in smaller quantities, could be cut with a laser, or by cut to length machine.
Silicon significantly increases the electrical resistivity from the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability in the material, particularly if rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen should be kept low, as these elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even during particles as small as one micrometer in diameter, increase hysteresis losses as well as decreasing magnetic permeability. The existence of carbon carries 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 contributing to an increase in power loss as time passes. For these reasons, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel inside a decarburizing atmosphere, including hydrogen.
Electrical steel made without special processing to manipulate crystal orientation, non-oriented steel, usually includes 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 normally abbreviated to CRNGO.
Grain-oriented electrical steel usually includes a silicon amount of 3% (Si:11Fe). It is processed in a manner how the optimal properties are created in the rolling direction, because of a tight control (proposed by Norman P. Goss) in 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 normally supplied by the producing mills in coil form and should be cut into “laminations”, which can be then used to form a transformer core, which happens to be a fundamental element of any transformer. Grain-oriented steel is used in large power and distribution transformers and also in certain audio output transformers.
CRNGO is cheaper than core cutting machine. It can be used when pricing is more important than efficiency as well as for applications where the direction of magnetic flux will not be constant, like in 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 is actually 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 fast that crystals will not form. Amorphous steel has limitations to foils of around 50 µm thickness. They have poorer mechanical properties so that as of 2010 it costs about double the amount as conventional steel, which makes it cost-effective simply for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of a single-third that relating to conventional electrical steels.
Electrical steel is generally coated to boost electrical resistance between laminations, reducing eddy currents, to supply effectiveness against corrosion or rust, and also to work as a lubricant during die cutting. There are various coatings, organic and inorganic, and also the coating used depends upon the use of the steel. The kind of coating selected depends on the temperature treatment of the laminations, whether the finished lamination will probably be immersed in oil, as well as the working temperature in the finished apparatus. Very early practice would be to insulate each lamination with a layer of paper or perhaps a varnish coating, but this reduced the stacking factor in the core and limited the maximum temperature of your core.
The magnetic properties of electrical steel are determined by heat treatment, as improving the average crystal size decreases the hysteresis loss. Hysteresis loss is determined by a standard 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 a semi-processed state so that, after punching the last shape, one last heat treatment can be applied to make 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 does not 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 might also increase noise because of magnetostriction.
The magnetic properties of electrical steel are tested while using internationally standard Epstein frame method.
Electrical steel is more costly than mild steel-in 1981 it had been greater than twice the charge by weight.
The size of magnetic domains in Transformer core cutting machine may be reduced by scribing the surface of the sheet using a laser, or mechanically. This greatly reduces the hysteresis losses within the assembled core.