Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) can be a special steel tailored to make specific magnetic properties: small hysteresis area causing low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally made in cold-rolled strips below 2 mm thick. These strips are cut to contour around make laminations which are stacked together to produce the laminated cores of transformers, and also the stator and rotor of electric motors. Laminations might be cut with their finished shape from a punch and die or, in smaller quantities, can be cut with a laser, or by cut to length machine.
Silicon significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus reducing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability in the material, specially when rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen has to be kept low, as these elements indicate the presence of carbides, sulfides, oxides and nitrides. These compounds, in particles no more than one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The inclusion 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 causing a rise in power loss over time. For these reasons, the carbon level is kept to .005% or lower. The carbon level may be reduced by annealing the steel in a decarburizing atmosphere, including hydrogen.
Electrical steel made without special processing to manipulate crystal orientation, non-oriented steel, usually carries a silicon degree of 2 to 3.5% and it has similar magnetic properties in most directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is usually abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon degree of 3% (Si:11Fe). It really is processed in a way the optimal properties are created in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation in accordance with 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 utilized for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is usually supplied by the producing mills in coil form and has to be cut into “laminations”, which are then used produce a transformer core, which can be an integral part of any transformer. Grain-oriented steel is used in large power and distribution transformers as well as in certain audio output transformers.
CRNGO is less expensive than transformer core cutting machine. It can be used when cost is more significant than efficiency as well as for applications in which the 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 take advantage 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 at a rate around one megakelvin per second, so quick that crystals usually do not form. Amorphous steel is restricted to foils of about 50 µm thickness. It provides poorer mechanical properties so when of 2010 it costs about twice as much as conventional steel, so that it is inexpensive just for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of just one-third that of conventional electrical steels.
Electrical steel is usually coated to enhance electrical resistance between laminations, reducing eddy currents, to offer resistance to corrosion or rust, as well as work as a lubricant during die cutting. There are various coatings, organic and inorganic, along with the coating used is dependent upon the effective use of the steel. The sort of coating selected depends upon the temperature therapy for the laminations, whether the finished lamination will be immersed in oil, along with the working temperature of the finished apparatus. Very early practice was to insulate each lamination having a layer of paper or perhaps a varnish coating, but this reduced the stacking factor from the core and limited the maximum temperature of the core.
The magnetic properties of electrical steel are reliant on heat treatment, as boosting the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon a standard test and, for common grades of electrical steel, may cover anything 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 can be delivered in the semi-processed state in order that, after punching the ultimate shape, a final heat treatment can be applied to produce the normally required 150-micrometer grain size. Fully processed electrical steel is generally delivered with an 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, or even rough handling can adversely affect electrical steel’s magnetic properties and might also increase noise on account of magnetostriction.
The magnetic properties of electrical steel are tested utilizing 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 size of magnetic domains in Transformer core cutting machine might be reduced by scribing the top of the sheet using a laser, or mechanically. This greatly decreases the hysteresis losses inside the assembled core.