Eddy currents, or Foucault currents - induction volumetric electric currents formed in conductors due to the time variation of the magnetic field flux acting on them. Since the resistance of large conductors is small, the Foucault current can be quite large. The movement of current in a conductor, according to Lenz's rule, is carried out along the path of greatest resistance to the forces that caused it.
Content
- The history of the discovery of the phenomenon
- Vortex forces
- Use in flaw detection
- Application of Foucault currents
The history of the discovery of the phenomenon
For the first time this phenomenon discovered by the French scientist Arago in the twenties of the XIX century. On one axis, he installed a copper disk, and above it a magnetic needle. Then he began to rotate the arrow, as a result of which the disk also began to rotate.
This phenomenon was named after the scientist Arago. When Faraday discovered the law of electromagnetic induction a few years later, he was able to explain this phenomenon. The magnetic field rotated by the arrow leads to the appearance of an eddy current in the disk, which carried out its movement.
A more detailed study of this phenomenon was undertaken by the physicist Foucault, who revealed the heating of metal bodies as a result of exposure to a magnetic field. The Russian physicist Lenz also studied and experimented with vortex flows. He found that they had no effect on the change in the magnetic field from which they formed.
Vortex forces
To increase the efficiency of any mechanism, it is necessary to minimize the forces of vortex flows. To do this, increase the electrical resistance of the magnetic wire. The method of reducing the effect of eddy currents depends on the type of electrical device. Suppression of Foucault currents carried out in the following ways:
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When assembling transformers, the cores are drawn from thin insulated plates. This makes it possible to reduce the degree of heating caused by the action of the Foucault current. - The metal plates are positioned so that the direction of the eddy current is perpendicular to their boundaries.
- With the advent of ferrites, which have high resistance, it has become possible to manufacture solid cores.
And also during the casting of the core elements, silicon is added, which increases the electrical resistance. Sometimes they are used in assembling pieces of metal wire, which are preliminarily subjected to heat treatment.
In addition, special insulation gaskets are used. Such methods during assembly can significantly reduce the strength of the Foucault currents, as a result of which the efficiency of any unit increases.
Magnetic wires in high-frequency equipment are carefully insulated from each other and twisted into a bundle. Each twist is covered with a special insulating element. For the transmission of electrical energy over long distances, a multicore cable with insulated wires is used.
Use in flaw detection
Eddy current testing is one of the ways to check the structure of different materials. It is based on the analysis of the changes occurring in the interaction of the external electromagnetic field with the eddy currents of the object under study.
As a source of the electromagnetic field, an inductive coil is used, on the basis of which flaw detectors are produced. These devices produce quality control inspection of electrically conductive materials:
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metals and their alloys; - semiconductors;
- graphite, etc.
The electromagnetic field of Foucault currents in the tested object acts on the coil of the device, inducing an electromotive force in it or changing the electrical resistance. The change in coil voltage determines the properties and quality of the tested object.
In addition to flaw detectors, which detect breaks in the surface of materials, they produce devices for determining the structure and size of objects. On the basis of the use of eddy currents, an apparatus for detecting electrically conductive elements (metal detector) is manufactured.
Application of Foucault currents
Experts believe that when using Foucault currents, they have more harmful effects than positive ones. Nevertheless, they have found wide application in various areas of life. This is especially true in the following areas:
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metallurgical industry; - transport;
- computing technology;
- electrical engineering.
On the basis of eddy currents for metallurgy, units are produced that allow transporting and quenching molten metals. Induction furnaces are widely used in the same industry. In terms of their performance, they are much superior to similar devices, the work of which is based on other types of action.
In addition, the processes of melting and quenching metals are only possible using this phenomenon. In transport, when moving high-speed trains on magnetic cushions, brake systems are used, the principle of which is based on Foucault currents.
The creation of modern computer technology and transformers became possible only due to the use and improvement of vortex flows in their designs. And also they are used in vacuum devices, where they carry out a complete pumping out of air and other gases.
Such devices are highly economical and efficient. At present, physicists in many countries continue to study and experiment with this phenomenon. As a result, every year it is possible to improve devices and equipment operating on the principle of eddy currents.
