What are eddy currents and what measures are taken to reduce them

In electricity, there are a number of phenomena that specialists need to know. Although not all information can be useful in everyday practice, it can sometimes help to understand the cause of a problem. Eddy currents caused some technological tricks in the manufacture of electric 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.

Brief definition

Eddy currents are currents that flow in conductors under the influence of an alternating magnetic field. Not necessarily the field must change, the body can move in a magnetic field, all the same, a current will begin to flow in it.

Eddy currents

It is impossible to find the real trajectory of the 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 subject being in an alternating magnetic field or moving about the field.

Discovery story

In 1824, the scientist D.F. Arago conducted an experiment. He mounted a copper disk on one axis, placed a magnetic needle above it. As the magnetic needle rotates, the disk begins to move. So for the first time observed the phenomenon of eddy currents. 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 called, while the phenomenon of Arago.

After a couple of years, 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 arrow field.

Why is the second name Foucault currents? Because the physicist Foucault investigated in detail the phenomenon of eddy currents. In the course of his research, he made a great discovery. It consisted in the fact that bodies under the influence of eddy currents heat up. We have dealt with the theory, now we will talk about where Foucault currents are used and which 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 network transformer, you probably noticed that its core is made of thin sheets, although it might seem that it was easier to make a solid cast structure.

Transformer core

The fact is that they are struggling with eddy currents in this way. Foucault established the heating of the bodies in which they flow. Since the operation of the transformer is based on the principles of interaction of variable magnetic fields, eddy currents are inevitable.

Any heating of bodies is the release of energy in the form of heat. In this case, core losses will occur. How is this 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

Loss of energy in the magnetic circuit is 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 stray currents. Such losses are described by the formula by which it is possible to calculate:

Formula for calculating

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 isolated from each other by scale or a layer of varnish. The cores of large transformers are pulled together by an insulated stud. This reduces 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 electromagnets. The same applies to the design of parts of electric motors and a generator: a rotor and a stator.

Practical application

Now about the useful applications of Foucault currents. A huge contribution was made to metallurgy by the invention of induction steelmaking furnaces. They are arranged 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 is completely melted.

Steel furnace

Note of the author!The development of induction furnaces significantly increased the environmental friendliness of metal production and changed the idea of ​​smelting methods. I work at a metallurgical plant, where ten years ago they launched a new high-tech workshop with such installations, and a few years after the development of new equipment, the classic open-hearth was closed. 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 manufacture of vacuum devices. The problem is the complete removal of gases before sealing the flask. Using Foucault currents, the electrodes of the lamp 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 beneficial and harmful. In some cases, their influence does not entail electrical problems. For example, a pipeline laid near cable lines decays faster for no apparent third-party reasons. At the same time, induction heating devices have shown themselves quite well, especially since such a device for domestic use can be assembled yourself. We hope that now you know what Foucault eddy currents are, as well as what application they found in production and in everyday life.

Related materials:

(1 votes)
Loading...

Add a comment