Editing Magnetic core (section)

==== Laminated silicon steel ====
{{main article|Silicon steel}}
[[File:Laminated core eddy currents 2.svg|thumb|upright=1.4|''(left)'' Eddy currents ''(<span style="color:red;">I, red</span>)'' within a solid iron transformer core. ''(right)'' Making the core out of thin [[laminations]] parallel to the field ''(<span style="color:green;">B, green</span>)'' with insulation between them (''C'') limits the eddy currents to circulate within each individual lamination, reducing the total current.  In this diagram the field and currents are shown in one direction, but they actually reverse direction with the alternating current in the transformer winding.]]

In order to reduce the eddy current losses mentioned above, most low frequency power transformers and inductors use [[laminations|laminated]] cores, made of stacks of thin sheets of [[silicon steel]]:

===== Lamination =====
[[Image:EI Lam.jpg|thumb|right|Typical EI Lamination.]]

[[Lamination|Laminated]] magnetic cores are made of stacks of thin iron sheets coated with an insulating layer, lying as much as possible parallel with the lines of flux.  The layers of insulation serve as a barrier to eddy currents, so eddy currents can only flow in narrow loops within the thickness of each single lamination.  Since the current in an eddy current loop is proportional to the area of the loop, this prevents most of the current from flowing, reducing eddy currents to a very small level.   Since power dissipated is proportional to the square of the current, breaking a large core into narrow laminations reduces the power losses drastically.  From this, it can be seen that the thinner the laminations, the lower the eddy current losses.

===== Silicon alloying =====
A small addition of [[silicon]] to iron (around 3%) results in a dramatic increase of the [[resistivity]] of the metal, up to four times higher.{{citation needed|date=August 2011}}  The higher resistivity reduces the eddy currents, so [[silicon steel]] is used in transformer cores. Further increase in silicon concentration impairs the steel's mechanical properties, causing difficulties for rolling due to brittleness.

Among the two types of [[silicon steel]], grain-oriented (GO) and grain non-oriented (GNO), GO is most desirable for magnetic cores. It is [[anisotropic]], offering better magnetic properties than GNO in one direction. As the magnetic field in inductor and transformer cores is always along the same direction, it is an advantage to use grain oriented steel in the preferred orientation. Rotating machines, where the direction of the magnetic field can change, gain no benefit from grain-oriented steel.