Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to produce specific magnetic properties: small hysteresis area leading to low power loss per cycle, low core loss, and high permeability.
Electrical steel is normally created in cold-rolled strips lower than 2 mm thick. These strips are cut to contour around make laminations that are stacked together to produce the laminated cores of transformers, along with the stator and rotor of electric motors. Laminations might be cut to 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 boosts the electrical resistivity in 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 your material, especially when rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen has to be kept low, as these elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even during particles no more than one micrometer in diameter, increase hysteresis losses while decreasing magnetic permeability. The presence of carbon features a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it slowly leaves the solid solution and precipitates as carbides, thus resulting in a rise in power loss with time. Because of this, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel in the decarburizing atmosphere, like hydrogen.
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually carries a silicon degree of 2 to 3.5% and has 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 features a silicon level of 3% (Si:11Fe). It can be processed in such a manner 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 frequently abbreviated to CRGO.
CRGO is generally supplied by the producing mills in coil form and has to be cut into “laminations”, which can be then used to form a transformer core, which happens to be an integral part of any transformer. Grain-oriented steel is commonly used in large power and distribution transformers and in certain audio output transformers.
CRNGO is less expensive than core cutting machine. It really is used when expense is more significant than efficiency and then for applications where 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 take advantage 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 at a rate around one megakelvin per second, so fast that crystals tend not to form. Amorphous steel is limited to foils of approximately 50 µm thickness. It provides poorer mechanical properties so that as of 2010 it costs about double the amount as conventional steel, making it cost-effective exclusively for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of a single-third that relating to conventional electrical steels.
Electrical steel is often coated to increase electrical resistance between laminations, reducing eddy currents, to supply effectiveness against corrosion or rust, and also to work as a lubricant during die cutting. There are several coatings, organic and inorganic, and the coating used is determined by the effective use of the steel. The type of coating selected is determined by the heat management of the laminations, regardless of if the finished lamination is going to be immersed in oil, as well as the working temperature in the finished apparatus. Very early practice would be to insulate each lamination by using a layer of paper or possibly a varnish coating, but this reduced the stacking factor of your core and limited the utmost temperature of the core.
The magnetic properties of electrical steel are reliant on heat treatment, as improving the average crystal size decreases the hysteresis loss. Hysteresis loss is dependent upon an ordinary test and, for common grades of electrical steel, may range between 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 could be delivered inside a semi-processed state so that, after punching the final shape, your final heat treatment can be applied to create 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, and even 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 while using internationally standard Epstein frame method.
Electrical steel is far more costly than mild steel-in 1981 it was a lot more than twice the cost by weight.
How big magnetic domains in Silicon steel cut to length can be reduced by scribing the surface of the sheet using a laser, or mechanically. This greatly reduces the hysteresis losses inside the assembled core.