Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is really a special steel tailored to generate specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally created in cold-rolled strips below 2 mm thick. These strips are cut to contour around make laminations that happen to be stacked together to form the laminated cores of transformers, along with the stator and rotor of electric motors. Laminations could be cut for their finished shape by a punch and die or, in smaller quantities, can be cut by a laser, or by cut to length machine.
Silicon significantly raises the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus decreasing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of 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 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 actual existence of carbon carries 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 an increase in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level might be reduced by annealing the steel inside a decarburizing atmosphere, such as hydrogen.
Electrical steel made without special processing to manipulate crystal orientation, non-oriented steel, usually features a silicon level of 2 to 3.5% and contains similar magnetic properties in most directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is usually abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon amount of 3% (Si:11Fe). It is actually processed in such a manner that the optimal properties are created in the rolling direction, as a result of tight control (proposed by Norman P. Goss) of your 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 really is used 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”, that are then used to form a transformer core, which is a fundamental part of any transformer. Grain-oriented steel is commonly used in large power and distribution transformers and also in certain audio output transformers.
CRNGO is less expensive than cut to length. It can be used when expense is more essential than efficiency and for applications where the direction of magnetic flux is not constant, as with electric motors and generators with moving parts. You can use it if you find insufficient space to orient components to leverage 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 around one megakelvin per second, so quickly that crystals will not form. Amorphous steel is restricted to foils of about 50 µm thickness. It offers poorer mechanical properties so when of 2010 it costs about double the amount as conventional steel, rendering it inexpensive exclusively for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of merely one-third that from conventional electrical steels.
Electrical steel is normally coated to boost electrical resistance between laminations, reducing eddy currents, to deliver effectiveness against corrosion or rust, and also to serve as a lubricant during die cutting. There are various coatings, organic and inorganic, and also the coating used is determined by the application of the steel. The particular coating selected depends upon the heat treatments for the laminations, regardless of if the finished lamination will be immersed in oil, along with the working temperature in the finished apparatus. Very early practice would be to insulate each lamination by using a layer of paper or a varnish coating, but this reduced the stacking factor of your core and limited the maximum temperature in 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 a regular 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 inside a semi-processed state in order that, after punching the last shape, a final heat treatment does apply to produce 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 fails 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 could also increase noise due to 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 was actually greater than twice the cost by weight.
How big magnetic domains in Transformer core cutting machine could be reduced by scribing the top of the sheet by using a laser, or mechanically. This greatly reduces the hysteresis losses in the assembled core.