Magnetic core

As iron core transformer core or also called short core is called a made ​​of ferromagnetic materials or ferrites and thus magnetizable solid or layer-built body in electrical engineering.

Its main task is to bring together, in conjunction with current-carrying coils the magnetic flux and to increase the inductance and the magnetic flux density.

When laminated iron cores of a laminated core ( from transformer sheets ) or an iron package is spoken. The plates isolated from each other are required on alternating fields in order to avoid eddy current losses.

  • 3.1 Examples of use

Basics

A coil through which an electric current, a magnetic field is built up around the spool. This magnetic effect is achieved by a core of a ferromagnetic substance (iron, nickel or cobalt ) is very strong, with certain materials, more than 10,000 times, is increased. The iron core improves the magnetic conductivity, whereby the magnetic flux is concentrated can be led to where he is to act. It reduces the number of windings in transformers the primary coil.

As ferromagnetic materials have below the Curie temperature ( for example, iron 768 ° C) molecular magnets inside. By the iron core, the magnetic flux is directed in certain pathways, this is particularly the case with annular closed ferrite cores with low leakage flux. However, the magnetic conductivity is approximately constant and depends on the magnetic flux density. At high densities, the material loses its high magnetic conductivity and this is reduced in the extreme case, which is referred to as saturation, μ0 is the vacuum on.

Construction

In the construction of iron cores, it is necessary to take into account a plurality of magnetic sizes:

  • Magnetic field strength
  • Magnetic flux density
  • The inductance
  • Possibly occurring eddy currents
  • The permeability ( magnetic permeability of the core material )

Depending on the field of application is the iron core of different ferromagnetic materials. It is important that materials with low iron losses as possible are used. Depending on the purpose magnetically hard or soft magnetic materials are used. These properties are apparent from the hysteresis loop. To optimize the effect of the iron core, the windings of the coils are made ​​so that the smallest possible space between the iron core and the coil body is formed.

Direct current

Since DC no eddy currents occur, the iron core can be made of solid iron here. This solid iron cores may consist of both cast iron and solid steel. However, in practice these iron cores are mainly made of electrical steel sheets. For small DC motors, the poles are often made ​​of ferrite magnets.

Low-frequency AC

The eddy current losses increase quadratically with the frequency and are so large that the solid iron core is strongly heated in massive iron cores. Due to these eddy currents occurring in alternating current and the associated eddy current losses, the iron cores for this use of layered and mutually insulated electrical steel sheets are produced. From these sheets, depending on the application, different cuts (M - EI - UI) stamped or rolled up into so-called tape-wound cores and processed.

High frequency alternating

For high-frequency alternating iron cores are made ​​of insulating material mixed with iron powder, iron powder cores so-called manufactured. The insulating bar between the metallic magnetic particles, reducing the eddy currents, as long as the frequency is not very high. There are also formed for the magnetic field disruptions, this allows only a relatively low permeability.

Another material for high frequencies are ferrites. These are ceramic materials based on oxides, and depending on the composition insulator or poor conductor. It is produced by sintering. Due to the low electrical conductivity occur in them even at high frequencies hardly eddy currents. At very high frequencies, no iron core is used.

Areas of application

Application areas are located where a targeted guiding the magnetic flux according to the electric current is required or where the inductance of a coil must be increased.

Examples of use

  • Transformers
  • Inductors
  • Electric motors, generators
  • Relay
  • Solenoids, pull magnets
  • Magnetic heads

Source:

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