Electrical steel

The size of magnetic domains in the sheet can be reduced by scribingthe surface of the sheet with a laser, or mechanically. This greatlyreduces the hysteresis losses in the assembled core.

Core steel is much more costly than the mild steel used forapparatus tanks, generator frames, etc. - in 1981 it was more thantwice the cost per unit weight.

For certain , cores made of amorphous steel are used. This material is a prepared by pouring molten alloy steel on a rotating cooled wheel,which cools the metal so quickly (a rate of about one million degreesper second) that crystals do not form. The resulting may have losses due to the core material only one-third that ofconventional steels. However, its high cost (about twice that ofconventional steel) and lower mechanical properties make use ofamorphous steel economical only for certain distribution-typetransformers.

The magnetic properties of electrical steel are dependent on ,as increasing the average crystal size decreases the hysteresis loss.Hysteresis loss is determined by a standard test and for common gradesof electrical steel may range from about 2 to 10 watts per kilogram (1to 5 watts per pound) at 60 Hz and 1.5 tesla magnetic field strength.Semi-processed electrical steels are delivered in a state that, afterpunching the final shape, a final heat treatment develops the desired150-micrometer grain size. The fully processed steels are usuallydelivered with coating, full heat treatment, and defined magnetic properties, forapplications where the punching operation does not significantlydegrade the material properties. Excessive bending, incorrect heattreatment, or even rough handling of core steel can adversely effectits magnetic properties and may also increase noise due to

Electrical steel is usually coated to increase electrical resistance between laminations, to provide resistance to or , and to act as a lubricant during the cutting. There are various coatings, and , and the coating used depends on the application of the steel.The type of coating selected depends on the heat treatment of thelaminations, whether the finished lamination will be immersed in oil,and the working temperature of the finished apparatus. Former practicewas to insulate each lamination with a layer of paper or a varnishcoating, but this reduced the stacking factor of the core and limitedthe maximum temperature of the core.

Non-oriented electrical steel usually has a silicon level of2 to 3.5% and has similar magnetic properties in all directions, whichmakes it .It is less expensive and is used in applications where the direction ofmagnetic flux is changing, such as electric motors and generators. Itis also used when efficiency is less important or when there isinsufficient space to correctly orient components to take advantage ofthe properties of grain-oriented electrical steel.

Grain-oriented electrical steel usually has a silicon levelof 3% (Si:11Fe). It is processed in such a way that the optimumproperties are developed in the rolling direction, due to a tightcontrol (proposed by ) of the crystal orientation relative to the sheet. Due to the special orientation, the density is increased by 30% in the coil rolling direction, although its is decreased by 5%. It is used for the cores of high-efficiency , and .

There are two main types of electrical steel: grain-oriented and non-oriented.

Increasing the amount of silicon inhibits eddy currents and narrows the of the material, thus lowering the .However, the grain structure hardens and embrittles the metal, whichadversely affects the workability of the material, especially whenrolling it. When alloying, the concentration levels of , , and must be kept low, as these elements indicate the presence of carbides,sulfides, oxides and nitrides. These compounds, even in particles assmall as one micrometer in diameter, increase while also decreasing . The presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes aging when it slowly leaves the solid solution and precipitates ascarbides, thus resulting in an increase in power loss over time. Forthese reasons, the carbon level is kept to 0.005% or lower. The carbonlevel can be reduced by the steel in a atmosphere, such as .

Electrical steel is an iron alloy which may have from zero to 6.5%silicon (Si:5Fe). Silicon significantly increases the electricalresistivity of the steel, which decreases the induced and thus reduces the core loss. Manganese and can be added up to 0.5%.

The material is usually manufactured in the form of strips less than 2 mm thick. These strips are called when stacked together to form a core. Once assembled, they form the of or the and parts of . Laminations may be cut to their finished shape by a punch and die, or in smaller quantities may be cut by a laser, or by .

Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty tailored to produce certain properties, such as a small area (small energy dissipation per cycle, or low ) and high .

Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty steel