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 high permeability.
Electrical steel is often made in cold-rolled strips lower than 2 mm thick. These strips are cut to contour around make laminations which are stacked together to make the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations might be cut with their finished shape with a punch and die or, in smaller quantities, may be cut by way of a laser, or by cut to length machine.
Silicon significantly raises the electrical resistivity from the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus decreasing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material, specially when rolling it. When alloying, the concentration degrees of carbon, sulfur, oxygen and nitrogen needs to be kept low, because they elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, in particles as small as one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The actual existence of carbon features a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it slowly leaves the solid solution and precipitates as carbides, thus resulting in a rise in power loss as time passes. Because of this, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel in a decarburizing atmosphere, like 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 every directions, i.e., it can be isotropic. Cold-rolled non-grain-oriented steel is normally abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon degree of 3% (Si:11Fe). It is processed in a manner how the optimal properties are developed 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% in 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 usually abbreviated to CRGO.
CRGO is generally provided by the producing mills in coil form and must be cut into “laminations”, which can be then used to make a transformer core, which is an integral part of any transformer. Grain-oriented steel is utilized in large power and distribution transformers as well as in certain audio output transformers.
CRNGO is more affordable than transformer core cutting machine. It can be used when pricing is more important than efficiency as well as for applications where direction of magnetic flux is not really constant, as with electric motors and generators with moving parts. It can be used if you find insufficient space to orient components to benefit from the directional properties of grain-oriented electrical steel.
This material is really 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 quickly that crystals tend not to form. Amorphous steel has limitations to foils of around 50 µm thickness. It has poorer mechanical properties and also as of 2010 it costs about double the amount as conventional steel, rendering it cost-effective just for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of one-third that relating to conventional electrical steels.
Electrical steel is generally coated to improve electrical resistance between laminations, reducing eddy currents, to deliver potential to deal with corrosion or rust, and to behave as a lubricant during die cutting. There are many coatings, organic and inorganic, and also the coating used depends upon the application of the steel. The particular coating selected is dependent upon the heat management of the laminations, whether the finished lamination is going to be immersed in oil, and also the working temperature of your finished apparatus. Very early practice would be to insulate each lamination having a layer of paper or even a varnish coating, but this reduced the stacking factor from the core and limited the highest temperature from the core.
The magnetic properties of electrical steel are dependent on heat treatment, as increasing the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon a typical 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 might be delivered within a semi-processed state to ensure that, after punching the very last shape, a final heat treatment does apply to make the normally required 150-micrometer grain size. Fully processed electrical steel is often 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, or even rough handling can adversely affect electrical steel’s magnetic properties and may even also increase noise on account of magnetostriction.
The magnetic properties of electrical steel are tested using the internationally standard Epstein frame method.
Electrical steel is a lot more costly than mild steel-in 1981 it was greater than twice the cost by weight.
The actual size of magnetic domains in crgo cutting machine could be reduced by scribing the surface of the sheet having a laser, or mechanically. This greatly cuts down on the hysteresis losses from the assembled core.