What are Eddy Currents

In this guide, we will explore all the fundamental factors about eddy current. If you want to learn what they are, their effects or usefulness – then read this guide for detailed information.

What are Eddy Currents?

Eddy currents represent the electric currents move across a conductive object if subjected to fluctuating magnetic field. They circulate in closed loops in the conductive material, within planes at right angle to the electromagnetic field.

They occur if there is change in the magnetic field about a static conductor or if a conductor moves across the electromagnetic field. Eddy currents may be useful in some applications, but can also be unwanted in others.

Eddy currents
Eddy currents

Eddy Currents History

François Arago, physicist, mathematician, and the 2nd president of the Second French Republic was the first individual to notice eddy currents in 1824. In what has been referred to as rotatory magnetism, he distinguished it was possible to magnetize most conductive substances. These findings were later completed and expounded by Michael Faraday.

Emil Lenz formulated Lenz’s law in 1834. But it is Léon Foucault, a French scientist, who is acknowledged for discovering eddy currents. In 1855, The scientist determined that there is an increase in the force necessary to cause copper disk rotation when you position its rim between magnet poles. He also noted that the induced eddy currents heat up the disk.

Eddy Currents vs Eddy Losses

Eddy losses represent the dissipation of energy in heat form due to eddy currents circulation within conductive objects. Eddy currents experience resistance when flow through the material, which results in the heat dissipation. This energy loss can have adverse impacts in the functioning and efficiency of electrical transformers and equipment.

Eddy Losses
Eddy Losses

Summarily, eddy currents refer to the flowing electric currents generated in conductor materials due to changing electromagnetic fields. On the other hand, eddy losses describe the energy losses as heat due to these eddy currents. It is important to minimize eddy losses in order to enhance the working and effectiveness of electromagnetic appliances.

How Eddy Current are Produced

The eddy currents phenomenon is due to electromagnetic induction. When you introduce or there is a change in a magnetic field close to a conductive object, a magnetic flux is formed that penetrates the object.

The magnetic flux moving across the material changes with alterations in the induced electromagnetic field. Based on Faraday’s Law of electromagnetic induction, electric currents are produced by the changing magnetic flux.

These induced electric currents flow in a circular manner inside the conductor material, and what are known as eddy currents. The flow direction of the currents is dependent on the conductive material properties and magnetic field direction.

Eddy current production testing
Eddy current production testing

Causes of Eddy Currents

Typically, eddy currents are generated when there is variation in the magnetic field about a static conductor, or if a conductor moves across a magnetic field. Therefore, there is formation of eddy currents in instances where there is change in direction or intensity of electromagnetic field inside a conductor.

Hysteresis Vs Eddy Currents

Hysteresis and eddy currents are two dissimilar phenomena associated with the materials behavior within fluctuating magnetic fields. This magnetic fields fluctuation causes hysteresis in ferromagnetic materials and eddy currents within conductor objects.

Hysteresis loop
Hysteresis loop

The magnetic losses as a result of hysteresis are referred to as hysteresis loss whilst those caused by eddy currents are described as eddy current loss.

The table below compares hysteresis loss vs eddy current loss:

Hysteresis Loss Eddy Current Loss
Hysteresis loss happens because of magnetism reversal in a ferromagnetic material under varying magnetic field. Eddy current loss happens because of relative motion between the magnetic field and a conductor.
Takes place only within the core of an electrical device. Takes place within the core, conductor, and body of electrical device.
Happens in ferromagnetic materials Happens in conductive materials.
Hysteresis loss reduction involves using grain-oriented steel. Eddy current loss reduction entails utilizing lamination of metals to construct the lamination of the core.
Calculated applying the formula Pb = η * Bmaxn * f * V Calculated applying the formula P= Ke * Bmax2 * f2 * t* V

 

Eddy Currents Formula and Calculations

You can employ the formula below to determine the overall losses as a result of eddy currents:

P= Ke * Bmax2 * f2 * t* V

Where,

  • Pe represents eddy current loss (W)
  • Ke denotes eddy current constant.
  • Bmax denotes maximum flux density (Wb/m2)
  • f represents the induced voltage frequency (Hz)
  • t represents conductive material thickness (m)
  • V denotes the volume of conductor material (m3)

How to Minimize Eddy Currents

 

Minimizing eddy current losses is instrumental in enhancing the performance of electrical systems and devices. Here are some the methods of how to reduce eddy current losses:

Laminated Core

Incorporating laminated cores constructed using thin sheets of conducting material is a popular eddy current reduction technique in motors, transformers and additional electromagnetic gadgets. The thin sheets produce a greater electrical resistance towards the circulating current direction, hence minimizing eddy current losses.

High Resistivity Materials

Employing conductive materials having high electrical resistivity also assists in minimizing eddy current losses. They enable quick and efficient dissipation of eddy currents, which reduces losses.

Proper Core Design

Minimize the eddy currents path by optimizing the core design. For instance, you can use rectangular or toroidal cores rather than round cores to decrease the eddy current paths.

Control Frequency

There is direct proportionality between the fluctuating magnetic field frequency and eddy current losses. Though it might be difficult to eradicate eddy currents totally, decreasing the frequency can be instrumental in minimizing the losses in high-frequency applications.

Soft Magnetic Materials

Employ soft magnetic materials with low coercivity and high permeability. These materials type tend to exhibit reduced eddy current losses if exposed to fluctuating electromagnetic fields.

Magnetic Shielding

At times, magnetic shielding techniques can be applied to redirect or contain the magnetic fields. This inhibits their interaction with adjacent conductors, decreasing eddy currents induction.

Magnetic Coatings

Magnetic coating or insulation of the conductor surface can inhibit eddy currents development. The layer minimizes eddy current circulation by forming an obstacle between the fluctuating magnetic field and the conductor material.

Eddy Current Damping

This method of minimizing eddy current losses works by controlling motion or vibrations. You can lower unnecessary vibrations through the introduction of regulated eddy currents within specific parts.

Harmful Effects of Eddy Currents

 

Despite the many uses and benefits of eddy currents, they have some dangerous impacts as well. Some of the harmful eddy currents effects include:

Heating of Components

You may experience excess components heating as a result of eddy currents. This is especially a challenge when you use materials having high electrical conductivity or in high-frequency applications. The heating may lead to material deterioration, thermal stress, and reduced service life of the impacted components.

Energy Loss

There is possibility of conductive materials encountering considerable energy losses due to eddy currents. This may cause ineffectiveness in electrical systems and devices.

Eddy currents produce resistance as they flow across a conducting material, transforming the electrical energy to heat energy. Consequently, this energy conversion can lower the efficiency of generators, motors, transformers and additional electrical devices.

Noise and Vibration

There is also chance of induced audible noise and mechanical vibrations by eddy currents within conductive substances and neighboring structures. This means that the phenomenon can have adverse impacts in uses where low noise and accuracy are critical, like in sensitive audio equipment or scientific instruments.

Electromagnetic Interference (EMI)

Electromagnetic field creation because of eddy currents can interfere with adjacent electronic gadgets and circuitry. The EMI may result in disruptions, breakdown and signal distortion in delicate electronic devices. This can cause data corruption, communication errors, and additional functioning problems.

Magnetic Drag

Mobile conductor objects might experience magnetic drag caused by eddy currents, which counters the conductor movement. This may be undesirable if you intending to attain accurate control or positioning or in some mechanical equipment.

Applications of Eddy Currents

The most essential and prevalent uses of eddy currents include:

Magnetic Levitation

Magnetic levitation is a repulsive form of levitation that is applied in advanced high-speed maglev commuter trains to facilitate frictionless transportation. A superconducting magnet mounted on the train generates fluctuating magnetic flux.

This in turn generates eddy currents over the static conducting sheet on which the train levitates. The interaction of the magnetic field and eddy currents produces the levitation forces.

Induction Furnace

Induction furnace is common in smelting sector, where you put the metal you want to melt within a swiftly varying high-induced current. This current generates greater heat amount that melts the metal. Therefore, induction furnace helps in metal extraction from the ore.

Induction Motor

Eddy currents are instrumental in the rotation of induction motor. This happens when the system exposes the induced currents to the metallic rotor circling within the electromagnetic field. Consequently, there is decrease in relative speed between the field and rotor, making the induction to spin in the magnetic field direction.

Speedometer

The vehicle speedometer features a magnet, tied using hair strings, is fixed on the primary shaft of the motor vehicle. With every vehicle movement, the magnet shifts and displays the speed of the car through the hair strings.

Electric Brakes

Eddy currents play a significant role in the braking of trains, toller coasters, and electric drill or saw for its emergency cutout. The brakes subject the metallic wheels to an electromagnetic field, leading to an eddy current. As a result, the exchange between the generated eddy currents and applied field decelerates the wheels.

Faster spinning of the wheels will lead to more notable effect. This implies that eddy currents make it possible to decelerate a fast-moving machine without creating any discomfort.

Galvanometer

Another application of eddy currents is in galvanometers. Here, the eddy currents are applied to counteract the galvanometer deflection to ensure that the coil utilized inside the device attains equilibrium.

It facilitates the establishment of the galvanometer accuracy. This is because you cannot typically read the deflection till the testing operation and coil utilized settles.

Energy Meter

The armature coil inside an energy meter features an aluminum disc which circles in the paired permanent horseshoe magnet poles. The induced eddy currents produce a braking effect, and the power used is directly correlated to the divergence.

Metal Detector

With the aid of eddy currents induction, metal detectors help sense metals presence in soils, rocks etc. They are also employed by security forces to detect landmines, explosives, and weapons.

Metal Separation

Eddy currents and magnetic damping may also be applied in recycling centers for separation of metals from non-metals. This applies to all metal types, not only the ferromagnetic kinds like steel and iron.

Surface Inspection

Many techniques for finding discontinuity or irregularity on materials surfaces make use of the eddy currents phenomenon. Eddy current testing falls under non-destructive testing method, where the metal being tested is not interfered with.

Any flaw in the metal, such as near-surface fissure, cuts out the eddy current, consequently lowering the electromagnetic field. It is easy to sense this magnetic field variation.

Conclusion

As you can see, eddy currents have both benefits and limitations depending on the area of application. If you have any questions or inquiries about this interesting phenomenon, we are here to help.

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