What is Eddy Current? Where to use?

When an electrically conductive object moves in a magnetic field or is surrounded by a time varying magnetic field, currents are induced in it. If the conductor is a long wire or coil, the direction of the induced current is clearly indicated. In three-dimensional or two-dimensional metal parts, the flow direction is subject to turbulent changes. Such ring currents are called eddy currents. On the one hand, they are used, for example, in eddy current brakes, but on the other hand, they cause energy losses (eddy current losses) in many electrical machines such as transformers and generators and must be kept as small as possible here.

Discovery of the Eddy Current

In 1824, the scientist D.F. Arago was experimenting. He placed a copper disk on an axis, placed a magnetic needle on top of it. When the magnetic needle turned, the disc began to move. Thus, the phenomenon of eddy currents was observed for the first time. The disk began to rotate due to the flow of currents, the appearance of a magnetic field interacting with the arrow. It was later called the Arago phenomenon.

A few years later, M. Faraday, who discovered the law of electromagnetic induction, explained this phenomenon as follows: a moving magnetic field induces a current in the disk (as in a closed circuit) and interacts with the arrow field.

See Also: What is Electric Current? Unit and Types of Current?

Damages Caused by Eddy Currents

If you’ve ever thought about the design of a 50 Hz network transformer, you’ve probably noticed that although it may seem easier to make a one-piece cast structure, its core is made of thin sheets.

The fact is that this is how they fight eddy currents. Foucault established the warming of the bodies in which they flow. Since the operation of the transformer is based on the principles of the interaction of alternating magnetic fields, eddy currents are inevitable.

When it happens very close to the body, it can cause damage due to intense heat. In this case, core losses will occur. Why is it dangerous? Overheating in electrical systems leads to deterioration of cable windings. Eddy currents depend on the magnetic properties of the core.

How to Reduce Losses

Energy losses in the magnetic circuit do not benefit, how to deal with them? To reduce their value, the core is taken from thin plates of electrical steel – these are a kind of preventive measures to reduce parasitic currents. Such losses are defined by a formula from which it is possible to calculate:

As you know: the smaller the cross section of the conductor, the greater its resistance, and the greater the resistance, the less 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 hairpin. This reduces core losses, ie. these are the main ways of reducing Foucault currents.

What are the consequences of this phenomenon? As the currents occur, the field from which they emerge begins to weaken. So eddy currents reduce the power of electromagnets.

Eddy Current Usage Areas

Now about the useful applications of Foucault’s currents. A major contribution to metallurgy was made with the invention of induction steelmaking furnaces. It is designed in such a way that a molten metal mass is placed inside a coil through which a high frequency current flows. Its magnetic field induces large currents in the metal until it melts completely.

An example usage video we saw on a channel on Youtube;

They are used in metallurgy, as well as in the manufacture of electrovacuum devices. The problem is that the gases are completely removed before closing the bottle. With the help of Foucault currents, the electrodes of the lamp are heated to high temperatures, thereby deactivating the gas. In everyday life, you can find kitchen induction cookers, in which dishes are cooked thanks to the application of this phenomenon. Eddy currents also have some advantages and disadvantages.

Foucault’s currents are both beneficial and harmful. In some cases, their effects cause non-electrical problems. For example, a pipeline laid near cable lines will rot faster for no apparent third-party cause. At the same time, induction heating devices have proven themselves quite well, especially since such a device for domestic use can be assembled by yourself. We hope you now know what Foucault eddy currents are and what applications they find in production and everyday life.

Source: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/eddy-current