Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to produce specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally produced in cold-rolled strips less than 2 mm thick. These strips are cut to contour around make laminations which are stacked together to make the laminated cores of transformers, and also the stator and rotor of electric motors. Laminations can 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 improves the electrical resistivity of 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 from the material, especially when rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen must be kept low, as these elements indicate the actual existence of carbides, sulfides, oxides and nitrides. These compounds, in particles as small as one micrometer in diameter, increase hysteresis losses while decreasing magnetic permeability. The actual existence of carbon has 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 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 may be reduced by annealing the steel within a decarburizing atmosphere, such as hydrogen.
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually features a silicon amount of 2 to 3.5% and it has similar magnetic properties in all of the directions, i.e., it is isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually features a silicon level of 3% (Si:11Fe). It can be processed in a manner that this 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% from the coil rolling direction, although its magnetic saturation is decreased by 5%. It can be utilized 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 needs to be cut into “laminations”, that are then used to make a transformer core, which can be a fundamental part of any transformer. Grain-oriented steel is commonly used in large power and distribution transformers and in certain audio output transformers.
CRNGO is more affordable than cut to length. It can be used when expense is more significant than efficiency and then for applications where the direction of magnetic flux is not really constant, like in electric motors and generators with moving parts. You can use it when there is insufficient space to orient components to leverage 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 tend not to form. Amorphous steel is limited to foils of around 50 µm thickness. It offers poorer mechanical properties so when of 2010 it costs about twice as much as conventional steel, rendering it cost-effective simply for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of one-third that of conventional electrical steels.
Electrical steel is often coated to enhance electrical resistance between laminations, reducing eddy currents, to provide resistance to corrosion or rust, as well as to behave as a lubricant during die cutting. There are various coatings, organic and inorganic, as well as the coating used depends on the effective use of the steel. The type of coating selected depends on the high temperature treatment of the laminations, regardless of if the finished lamination will probably be immersed in oil, and also the working temperature of your finished apparatus. Very early practice ended up being to insulate each lamination with a layer of paper or a varnish coating, but this reduced the stacking factor from the core and limited the utmost temperature in the core.
The magnetic properties of electrical steel are determined by heat treatment, as enhancing the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon an ordinary 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 to ensure, after punching the final shape, one final 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 will not significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or perhaps rough handling can adversely affect electrical steel’s magnetic properties and could also increase noise because of magnetostriction.
The magnetic properties of electrical steel are tested making use of the internationally standard Epstein frame method.
Electrical steel is a lot more costly than mild steel-in 1981 it had been a lot more than twice the charge by weight.
The size of magnetic domains in crgo cutting machine might be reduced by scribing the top of the sheet with a laser, or mechanically. This greatly decreases the hysteresis losses inside the assembled core.