Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to generate specific magnetic properties: small hysteresis area causing low power loss per cycle, low core loss, and permeability.
Electrical steel is normally 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 produce the laminated cores of transformers, and also the stator and rotor of electric motors. Laminations could be cut for their finished shape with a punch and die or, in smaller quantities, can be cut from a laser, or by Core cutting machine.
Silicon significantly increases the electrical resistivity of 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 of the material, particularly when rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen must be kept low, because these elements indicate the inclusion of carbides, sulfides, oxides and nitrides. These compounds, even just in particles as small as one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The actual existence of carbon features a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging if it slowly leaves the solid solution and precipitates as carbides, thus leading to an increase in power loss with time. Because of this, 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 includes a silicon measure of 2 to 3.5% and has similar magnetic properties in all of the directions, i.e., it is isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon degree of 3% (Si:11Fe). It is processed in such a manner that this optimal properties are developed in the rolling direction, due to a tight control (proposed by Norman P. Goss) from the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% inside the coil rolling direction, although its magnetic saturation is decreased by 5%. It is used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is frequently abbreviated to CRGO.
CRGO is generally provided by the producing mills in coil form and has to be cut into “laminations”, that happen to be then used to form a transformer core, that is a fundamental element 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 core cutting machine. It really is used when pricing is more significant than efficiency and for applications where the direction of magnetic flux is just not constant, as with electric motors and generators with moving parts. It can be used if you find insufficient space to orient components to leverage the directional properties of grain-oriented electrical steel.
This material is actually 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 quick that crystals will not form. Amorphous steel is limited to foils of approximately 50 µm thickness. It has poorer mechanical properties and as of 2010 it costs about twice as much as conventional steel, which makes it inexpensive only for some distribution-type transformers.Transformers with amorphous steel cores may have core losses of just one-third that relating to conventional electrical steels.
Electrical steel is normally coated to enhance electrical resistance between laminations, reducing eddy currents, to deliver effectiveness against corrosion or rust, and to behave as a lubricant during die cutting. There are several coatings, organic and inorganic, as well as the coating used is determined by the effective use of the steel. The sort of coating selected is determined by the warmth therapy for the laminations, whether or not the finished lamination will be immersed in oil, along with the working temperature of your finished apparatus. Very early practice would be to insulate each lamination by using a layer of paper or possibly a varnish coating, but this reduced the stacking factor from the core and limited the most temperature of your 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 a regular 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 can be delivered inside a semi-processed state in order that, after punching the final shape, a final heat treatment does apply to produce 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 is not going to significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or perhaps rough handling can adversely affect electrical steel’s magnetic properties and may even also increase noise as a result 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 actually greater than twice the price by weight.
The actual size of magnetic domains in crgo cutting machine could be reduced by scribing the surface of the sheet using a laser, or mechanically. This greatly lessens the hysteresis losses in the assembled core.