Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is really a special steel tailored to create specific magnetic properties: small hysteresis area leading to low power loss per cycle, low core loss, and high permeability.
Electrical steel is often produced in cold-rolled strips less than 2 mm thick. These strips are cut to contour around make laminations which are stacked together to create the laminated cores of transformers, and also the stator and rotor of electric motors. Laminations can be cut on their finished shape by way of a punch and die or, in smaller quantities, can be cut with a laser, or by Core cutting machine.
Silicon significantly boosts the electrical resistivity of your steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus reducing 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 quantities of carbon, sulfur, oxygen and nitrogen needs to be kept low, as these elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even in particles as small as one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The inclusion of carbon has 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 leading to an increase in power loss after a while. For these reasons, the carbon level is kept to .005% or lower. The carbon level may 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 features a silicon amount of 2 to 3.5% and contains similar magnetic properties in every directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is usually abbreviated to CRNGO.
Grain-oriented electrical steel usually includes a silicon measure of 3% (Si:11Fe). It really is processed in such a way that this optimal properties are created in the rolling direction, because of 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 can be employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is normally abbreviated to CRGO.
CRGO is usually provided by the producing mills in coil form and should be cut into “laminations”, which can be then used produce a transformer core, which is a fundamental element of any transformer. Grain-oriented steel is used in large power and distribution transformers and also in certain audio output transformers.
CRNGO is more affordable than cut to length. It is used when expense is more significant than efficiency and also for applications where the direction of magnetic flux is not constant, as in electric motors and generators with moving parts. You can use it if you find insufficient space to orient components to take advantage 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 of approximately one megakelvin per second, so fast that crystals usually do not form. Amorphous steel has limitations to foils around 50 µm thickness. It offers poorer mechanical properties so when of 2010 it costs about double the amount as conventional steel, which makes it cost-effective just for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of a single-third that relating to conventional electrical steels.
Electrical steel is normally coated to improve electrical resistance between laminations, reducing eddy currents, to offer effectiveness against corrosion or rust, as well as act as a lubricant during die cutting. There are several coatings, organic and inorganic, as well as the coating used depends on the application of the steel. The sort of coating selected is dependent upon the heat therapy for the laminations, whether or not the finished lamination will be immersed in oil, as well as the working temperature of your finished apparatus. Very early practice ended up being to insulate each lamination using a layer of paper or possibly a varnish coating, but this reduced the stacking factor of the core and limited the maximum temperature in the core.
The magnetic properties of electrical steel are influenced by heat treatment, as improving the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon a standard 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 may be delivered in a semi-processed state in order that, after punching the final shape, a final heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is usually 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 even rough handling can adversely affect electrical steel’s magnetic properties and may also increase noise on account of magnetostriction.
The magnetic properties of electrical steel are tested using the internationally standard Epstein frame method.
Electrical steel is far more costly than mild steel-in 1981 it had been more than twice the cost by weight.
The dimensions of magnetic domains in crgo cutting machine may be reduced by scribing the top of the sheet with a laser, or mechanically. This greatly cuts down on the hysteresis losses from the assembled core.