Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to create specific magnetic properties: small hysteresis area contributing to low power loss per cycle, low core loss, and high permeability.
Electrical steel is often made in cold-rolled strips below 2 mm thick. These strips are cut to shape to make laminations that happen to be stacked together to produce the laminated cores of transformers, along with the stator and rotor of electric motors. Laminations may be cut for their finished shape by way of 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 of your 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 degrees of carbon, sulfur, oxygen and nitrogen should be kept low, because these elements indicate the presence of carbides, sulfides, oxides and nitrides. These compounds, even in particles no more than one micrometer in diameter, increase hysteresis losses as well as decreasing magnetic permeability. The presence of carbon features 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 causing an increase in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel inside a decarburizing atmosphere, for example hydrogen.
Electrical steel made without special processing to manipulate crystal orientation, non-oriented steel, usually has a silicon amount of 2 to 3.5% and has similar magnetic properties in most directions, i.e., it is isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon amount of 3% (Si:11Fe). It is processed in such a way that this optimal properties are created in the rolling direction, as a result of 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 employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is normally abbreviated to CRGO.
CRGO is often provided by the producing mills in coil form and needs to be cut into “laminations”, which are then used to create a transformer core, which can be an important part of any transformer. Grain-oriented steel is commonly used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is less costly than cut to length. It is actually used when expense is more significant than efficiency as well as for applications where direction of magnetic flux is not really constant, like electric motors and generators with moving parts. You can use it if you have insufficient space to orient components to make use of the directional properties of grain-oriented electrical steel.
This product can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price around one megakelvin per second, so quickly that crystals will not form. Amorphous steel is limited 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, so that it is inexpensive exclusively for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of a single-third those of conventional electrical steels.
Electrical steel is normally coated to increase electrical resistance between laminations, reducing eddy currents, to provide potential to deal with corrosion or rust, as well as to serve as a lubricant during die cutting. There are numerous coatings, organic and inorganic, as well as the coating used depends upon the effective use of the steel. The particular coating selected depends on the warmth management of the laminations, regardless of if the finished lamination is going to be immersed in oil, and the working temperature in the finished apparatus. Very early practice would be to insulate each lamination with a layer of paper or possibly a varnish coating, but this reduced the stacking factor from the core and limited the highest temperature of your core.
The magnetic properties of electrical steel are reliant on heat treatment, as enhancing the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon a regular test and, for common grades of electrical steel, may vary 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 can be delivered in a semi-processed state so that, after punching the final shape, one final heat treatment can be applied to produce the normally required 150-micrometer grain size. Fully processed electrical steel is often delivered having 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, and even rough handling can adversely affect electrical steel’s magnetic properties and could also increase noise due to magnetostriction.
The magnetic properties of electrical steel are tested utilizing the internationally standard Epstein frame method.
Electrical steel is more costly than mild steel-in 1981 it was greater than twice the charge by weight.
The actual size of magnetic domains in crgo cutting machine could be reduced by scribing the surface of the sheet by using a laser, or mechanically. This greatly lessens the hysteresis losses within the assembled core.