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 high permeability.
Electrical steel is usually made in cold-rolled strips less than 2 mm thick. These strips are cut to contour around make laminations that are stacked together to make the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations may be cut to their finished shape from a punch and die or, in smaller quantities, might be cut by way of a laser, or by Core cutting machine.
Silicon significantly increases the electrical resistivity of your steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus reducing 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, because they elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, in particles as small as one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The existence of carbon features a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging whenever it slowly leaves the solid solution and precipitates as carbides, thus contributing to an increase in power loss over time. Because of this, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel inside a decarburizing atmosphere, including 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 directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is normally abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon amount of 3% (Si:11Fe). It can be processed in such a way that this optimal properties are developed in the rolling direction, as a result of tight control (proposed by Norman P. Goss) in the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% within 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 often provided by the producing mills in coil form and should be cut into “laminations”, which can be then used to make a transformer core, that is a fundamental part of any transformer. Grain-oriented steel can be used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is more affordable than cut to length. It is used when cost is more essential than efficiency and also 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 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 around one megakelvin per second, so quick that crystals usually do not form. Amorphous steel is restricted to foils of about 50 µm thickness. It has poorer mechanical properties so when of 2010 it costs about double the amount as conventional steel, making it cost-effective simply for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of one-third that from conventional electrical steels.
Electrical steel is normally coated to boost electrical resistance between laminations, reducing eddy currents, to supply effectiveness against corrosion or rust, as well as to serve as a lubricant during die cutting. There are numerous coatings, organic and inorganic, and also the coating used is dependent upon the effective use of the steel. The kind of coating selected depends upon the high temperature therapy for the laminations, regardless of if the finished lamination will be immersed in oil, as well as the working temperature of your finished apparatus. Very early practice was to insulate each lamination by using a layer of paper or perhaps a varnish coating, but this reduced the stacking factor of the core and limited the maximum temperature of the core.
The magnetic properties of electrical steel are reliant on heat treatment, as increasing the average crystal size decreases the hysteresis loss. Hysteresis loss is dependent upon a regular test and, for common grades of electrical steel, may cover anything 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 could be delivered within a semi-processed state so that, after punching the final shape, one final heat treatment does apply to make the normally required 150-micrometer grain size. Fully processed electrical steel is often delivered with the 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 may even also increase noise as a result 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 absolutely was over twice the charge by weight.
How big magnetic domains in Silicon steel cut to length might be reduced by scribing the top of the sheet by using a laser, or mechanically. This greatly reduces the hysteresis losses from the assembled core.