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 contributing to low power loss per cycle, low core loss, and permeability.
Electrical steel is often created in cold-rolled strips under 2 mm thick. These strips are cut to shape to make laminations that are stacked together to create the laminated cores of transformers, and the stator and rotor of electric motors. Laminations could be cut for their finished shape with a punch and die or, in smaller quantities, might be cut with a laser, or by Core cutting machine.
Silicon significantly increases the electrical resistivity in 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 if rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen has to be kept low, because they elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even just in particles no more than one micrometer in diameter, increase hysteresis losses as well as decreasing magnetic permeability. The presence of carbon carries 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 a rise in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel within a decarburizing atmosphere, such as 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 it has similar magnetic properties in every directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually includes a silicon amount of 3% (Si:11Fe). It really is processed in a way how the optimal properties are created in the rolling direction, due to a tight control (proposed by Norman P. Goss) in the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% in the coil rolling direction, although its magnetic saturation is decreased by 5%. It can be useful for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is normally provided by the producing mills in coil form and should be cut into “laminations”, that are then used to make a transformer core, which can be a fundamental part of any transformer. Grain-oriented steel is utilized in large power and distribution transformers and also in certain audio output transformers.
CRNGO is cheaper than core cutting machine. It really is used when expense is more valuable than efficiency and then for applications the location where the direction of magnetic flux is just not constant, as in electric motors and generators with moving parts. You can use it should there be insufficient space to orient components to benefit from the directional properties of grain-oriented electrical steel.
This material can be 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 fast that crystals will not form. Amorphous steel has limitations to foils of about 50 µm thickness. They have poorer mechanical properties so when of 2010 it costs about twice as much as conventional steel, rendering it inexpensive only for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of one-third that relating to conventional electrical steels.
Electrical steel is usually coated to boost electrical resistance between laminations, reducing eddy currents, to offer potential to deal with corrosion or rust, as well as to act as a lubricant during die cutting. There are various coatings, organic and inorganic, and also the coating used is determined by the effective use of the steel. The sort of coating selected is dependent upon the temperature treatment of the laminations, if the finished lamination will be immersed in oil, as well as the working temperature of the finished apparatus. Very early practice was to insulate each lamination having a layer of paper or a varnish coating, but this reduced the stacking factor from the core and limited the highest temperature in the core.
The magnetic properties of electrical steel are influenced by heat treatment, as increasing the average crystal size decreases the hysteresis loss. Hysteresis loss is determined by an ordinary test and, for common grades of electrical steel, may range 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 in a semi-processed state to ensure, after punching the very last shape, one last heat treatment does apply to produce the normally required 150-micrometer grain size. Fully processed electrical steel is often delivered having an 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, and even rough handling can adversely affect electrical steel’s magnetic properties and may also increase noise because of magnetostriction.
The magnetic properties of electrical steel are tested utilizing the internationally standard Epstein frame method.
Electrical steel is much more costly than mild steel-in 1981 it was actually greater than twice the fee by weight.
The size of magnetic domains in Transformer core cutting machine might be reduced by scribing the top of the sheet with a laser, or mechanically. This greatly decreases the hysteresis losses within the assembled core.