Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is a special steel tailored to generate specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and permeability.
Electrical steel is often made in cold-rolled strips lower than 2 mm thick. These strips are cut to shape to make laminations that happen to be stacked together to form the laminated cores of transformers, and also the stator and rotor of electric motors. Laminations can be cut to their finished shape by way of a punch and die or, in smaller quantities, can be cut by a laser, or by cut to length machine.
Silicon significantly increases the electrical resistivity from the steel, which decreases the induced eddy currents and narrows the hysteresis loop in the material, thus reducing 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 levels of carbon, sulfur, oxygen and nitrogen needs to be kept low, since 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 presence of carbon carries 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. Therefore, the carbon level is kept to .005% or lower. The carbon level might be reduced by annealing the steel within a decarburizing atmosphere, like hydrogen.
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually carries a silicon level of 2 to 3.5% and contains similar magnetic properties in all directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is usually abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon measure of 3% (Si:11Fe). It is actually processed in such a manner that this optimal properties are created in the rolling direction, due to a tight control (proposed by Norman P. Goss) in the crystal orientation in accordance with the sheet. The magnetic flux density is increased by 30% within the coil rolling direction, although its magnetic saturation is decreased by 5%. It really is employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is usually abbreviated to CRGO.
CRGO is often provided 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 a fundamental element of any transformer. Grain-oriented steel can be used in large power and distribution transformers as well as in certain audio output transformers.
CRNGO is less expensive than core cutting machine. It can be used when cost is more important than efficiency and for applications the location where the direction of magnetic flux is not constant, like electric motors and generators with moving parts. It can be used when there is insufficient space to orient components to make use of the directional properties of grain-oriented electrical steel.
This product is 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 fast that crystals tend not to form. Amorphous steel is restricted to foils of around 50 µm thickness. It has poorer mechanical properties and as of 2010 it costs about twice as much as conventional steel, so that it is inexpensive simply for some distribution-type transformers.Transformers with amorphous steel cores may have core losses of just one-third that of conventional electrical steels.
Electrical steel is often coated to boost electrical resistance between laminations, reducing eddy currents, to supply resistance to corrosion or rust, and also to serve as a lubricant during die cutting. There are various coatings, organic and inorganic, and also the coating used depends upon the application of the steel. The type of coating selected is dependent upon the temperature therapy for the laminations, if the finished lamination is going to be immersed in oil, and also the working temperature in the 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 of the core and limited the highest temperature of the core.
The magnetic properties of electrical steel are dependent on heat treatment, as enhancing the average crystal size decreases the hysteresis loss. Hysteresis loss is determined by a regular test and, for common grades of electrical steel, may range between 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 might be delivered within a semi-processed state in order that, after punching the last shape, one final heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is normally delivered with the 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 perhaps rough handling can adversely affect electrical steel’s magnetic properties and might also increase noise due to magnetostriction.
The magnetic properties of electrical steel are tested using the internationally standard Epstein frame method.
Electrical steel is much more costly than mild steel-in 1981 it was actually a lot more than twice the fee by weight.
The dimensions of magnetic domains in crgo cutting machine might be reduced by scribing the top of the sheet using a laser, or mechanically. This greatly reduces the hysteresis losses in the assembled core.