Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) can be a special steel tailored to generate specific magnetic properties: small hysteresis area contributing to low power loss per cycle, low core loss, and permeability.
Electrical steel is generally made in cold-rolled strips lower 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, and also the stator and rotor of electric motors. Laminations may be cut with their finished shape by way of a punch and die or, in smaller quantities, might be cut from 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 of your material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability from the material, particularly when rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen must be kept low, since these elements indicate the presence of carbides, sulfides, oxides and nitrides. These compounds, even during particles no more than one micrometer in diameter, increase hysteresis losses as well as decreasing magnetic permeability. The presence of carbon has 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 over time. For these reasons, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel in the decarburizing atmosphere, such as hydrogen.
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually has a silicon measure of 2 to 3.5% and contains similar magnetic properties in all of the directions, i.e., it really is 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 a manner that the optimal properties are developed in the rolling direction, caused by 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 really is utilized for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is often supplied by the producing mills in coil form and needs to be cut into “laminations”, that are then used to form a transformer core, which can be an important part of any transformer. Grain-oriented steel is used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is cheaper than cut to length. It really is used when cost is more valuable than efficiency and for applications the location where the direction of magnetic flux will not be constant, like electric motors and generators with moving parts. You can use it when there is insufficient space to orient components to benefit from the directional properties of grain-oriented electrical steel.
This material can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price of around one megakelvin per second, so quick that crystals do not form. Amorphous steel is restricted to foils around 50 µm thickness. It offers poorer mechanical properties and as of 2010 it costs about twice as much as conventional steel, which makes it cost-effective just for some distribution-type transformers.Transformers with amorphous steel cores might have core losses of merely one-third that from conventional electrical steels.
Electrical steel is generally coated to enhance electrical resistance between laminations, reducing eddy currents, to supply effectiveness against corrosion or rust, and to serve as a lubricant during die cutting. There are many coatings, organic and inorganic, and the coating used depends upon the effective use of the steel. The sort of coating selected depends on the heat management of the laminations, if the finished lamination will probably be immersed in oil, and the working temperature from the finished apparatus. Very early practice ended up being to insulate each lamination with a layer of paper or possibly a varnish coating, but this reduced the stacking factor in the core and limited the utmost 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 a semi-processed state in order that, after punching the last shape, one last heat treatment does apply to form the normally required 150-micrometer grain size. Fully processed electrical steel is normally 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, as well as 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 making use of the internationally standard Epstein frame method.
Electrical steel is much more costly than mild steel-in 1981 it absolutely was greater than twice the price by weight.
The actual size of magnetic domains in Silicon steel cut to length could be reduced by scribing the surface of the sheet by using a laser, or mechanically. This greatly lessens the hysteresis losses in the assembled core.