Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is really a special steel tailored to produce specific magnetic properties: small hysteresis area causing low power loss per cycle, low core loss, and permeability.
Electrical steel is normally created in cold-rolled strips less than 2 mm thick. These strips are cut to contour around make laminations which are stacked together to form the laminated cores of transformers, and the stator and rotor of electric motors. Laminations could be cut on their finished shape with a punch and die or, in smaller quantities, can be cut by a laser, or by Core cutting machine.
Silicon significantly improves the electrical resistivity in the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability from the material, specially when rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen needs to be kept low, because they elements indicate the actual existence of carbides, sulfides, oxides and nitrides. These compounds, even just in particles no more than one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The existence 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. For these reasons, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, for example hydrogen.
Electrical steel made without special processing to control crystal orientation, non-oriented steel, usually features a silicon level of 2 to 3.5% and possesses similar magnetic properties in every directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually features a silicon degree of 3% (Si:11Fe). It really is processed in a manner the optimal properties are created in the rolling direction, because of a tight control (proposed by Norman P. Goss) from 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 is used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is normally abbreviated to CRGO.
CRGO is often supplied by the producing mills in coil form and must be cut into “laminations”, which are then used produce a transformer core, which is an integral part of any transformer. Grain-oriented steel is used in large power and distribution transformers and in certain audio output transformers.
CRNGO is more affordable than cut to length. It is used when cost is more significant than efficiency as well as for applications the location where the direction of magnetic flux will not be constant, like in electric motors and generators with moving parts. You can use it if you have insufficient space to orient components to make use of the directional properties of grain-oriented electrical steel.
This product is really 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 limited to foils around 50 µm thickness. It has poorer mechanical properties so that as of 2010 it costs about double the amount as conventional steel, so that it is inexpensive simply for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of just one-third that relating to conventional electrical steels.
Electrical steel is usually coated to enhance electrical resistance between laminations, reducing eddy currents, to supply potential to deal with corrosion or rust, and to behave as a lubricant during die cutting. There are numerous coatings, organic and inorganic, as well as the coating used is dependent upon the effective use of the steel. The kind of coating selected depends upon the temperature therapy for the laminations, whether the finished lamination will probably be immersed in oil, as well as the working temperature of your finished apparatus. Very early practice ended up being to insulate each lamination having a layer of paper or a varnish coating, but this reduced the stacking factor in the core and limited the highest temperature from 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 is determined by a standard test and, for common grades of electrical steel, may vary 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 may be delivered within a semi-processed state to ensure, after punching the last shape, a final heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is normally delivered having 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, as well as rough handling can adversely affect electrical steel’s magnetic properties and may even also increase noise due to magnetostriction.
The magnetic properties of electrical steel are tested while using internationally standard Epstein frame method.
Electrical steel is a lot more costly than mild steel-in 1981 it had been over twice the charge by weight.
The size of magnetic domains in Transformer core cutting machine could be reduced by scribing the surface of the sheet having a laser, or mechanically. This greatly lessens the hysteresis losses inside the assembled core.