There are a number of phenomena in electricity that professionals need to know. Although not all information can be useful in everyday practice, sometimes it will help to understand the cause of a problem. Eddy currents were the reason for the formation of some technological tricks in the manufacture of electrical machines and even became the basis for the principle of operation of some inventions. Let's see what Foucault eddy currents are and how they arise.
Content:
- Brief definition
- Discovery history
- Eddy current harm
- How to reduce losses
- Application in practice
Brief definition
Eddy currents are currents that flow in conductors under the influence of an alternating magnetic field on them. The field does not have to change, the body can move in a magnetic field, all the same, a current will begin to flow in it.
It is impossible to find a real trajectory for the movement of currents to take them into account, the current flows where it finds the path with the least resistance. Eddy currents always flow in a closed loop. The main conditions for its occurrence are the presence of an object in an alternating magnetic field or its movement relative to the field.
Discovery history
In 1824, the scientist D.F. Arago was conducting an experiment. He mounted a copper disk on one axis, and placed a magnetic needle above it. When the magnetic needle rotated, the disk began to move. This is how the phenomenon of eddy currents was observed for the first time. The disk began to rotate due to the fact that, due to the flow of currents, a magnetic field appeared, which interacted with the arrow. It was named then as the Arago phenomenon.
A couple of years later M. Faraday, who discovered the law of electromagnetic induction, explained this phenomenon in this way: a moving magnetic field induces a current in the disk (as in a closed loop) and it interacts with the field of the arrow.
Why is the second name Foucault currents? Because the physicist Foucault studied the phenomenon of eddy currents in detail. In the course of his research, he made a great discovery. It consisted in the fact that bodies are heated under the influence of eddy currents. With the theory sorted out, now we will talk about where Foucault currents are applied and which ones cause problems.
The video below provides a more detailed definition of this phenomenon:
Eddy current harm
If you were considering the design of a 50 Hz mains transformer, you probably noticed that its the core is made up of thin sheets, although it may seem that it was easier to make a solid cast design.
The fact is that this is how eddy currents are dealt with. Foucault established the heating of bodies in which they flow. Since the operation of the transformer is based on the principles of interaction of alternating magnetic fields, eddy currents are inevitable.
Any heating of bodies is the release of energy in the form of heat. In this case, core loss will occur. Why is it dangerous? In an electrical installation, strong heating leads to the destruction of the insulation of the windings and the failure of the machine. Eddy currents depend on the magnetic properties of the core.
How to reduce losses
Energy losses in the magnetic circuit are not useful, then how to deal with them? To reduce their size, the core is recruited from thin plates of electrical steel - this is a kind of preventive measure to reduce parasitic currents. Such losses are described by the formula by which the calculation can be made:
As you know: the smaller the cross-section of the conductor, the greater its resistance, and the greater its resistance, the lower the current. The plates are insulated from each other with scale or a layer of varnish. The cores of large transformers are pulled together with an insulated pin. This reduces the core loss, i.e. these are the main ways to reduce Foucault currents.
What are the consequences of the influence of this phenomenon? The magnetic field arising from the flow of Foucault currents weakens the field due to which they arose. That is, eddy currents reduce the strength of the electromagnets. The same applies to the design of electric motor and generator parts: rotor and stator.
Application in practice
Now about the useful areas of application of Foucault currents. A huge contribution was made to metallurgy with the invention of induction steel-making furnaces. They are designed in such a way that the molten mass of metal is placed inside a coil through which a high frequency current flows. Its magnetic field induces large currents inside the metal until it completely melts.
Author's note! The development of induction furnaces has significantly improved the environmental friendliness of metal production and changed the concept of smelting methods. I work at a metallurgical plant, where a new high-tech workshop was launched ten years ago with such installations, and a few years after the development of new equipment, the classic open-hearth. This indicates the productivity of this method of heating metals. Eddy currents are also used for surface hardening of metal.
Visual application in practice:
In addition to metallurgy, they are used in the production of electric vacuum devices. The problem is the complete evacuation of gases before sealing the flask. With the help of Foucault currents, the lamp electrodes are heated to high temperatures, thus deactivating the gas.
In everyday life, you can find induction cookers on which food is cooked, thanks to the application of this phenomenon. As you can see, eddy currents have their pros and cons.
Foucault currents are both good and bad. In some cases, their influence does not lead to electrical problems. For example, a pipeline laid near cable lines rots faster for no apparent third-party reason. At the same time, induction heating devices have shown themselves to be quite good, especially since such a device for domestic use can be assembled by yourself. We hope that now you know what Foucault's eddy currents are, as well as what application they found in production and in everyday life.
Related materials:
- How to make an induction boiler with your own hands
- The dependence of the resistance of the conductor on temperature
- The gimlet's rule in simple words