Electrical Eddy Current
Electrical eddy current is the current that originates within the current carrying conductor by changing magnetic field due to Faraday’s law of induction. Eddy current circulates in a closed loop within the conductor, perpendicular to the magnetic field that generates it. It may generate when a conductor is exposing to magnetic field or when a moving magnetic field gets closer to a stationary metallic conductor. That means:
“Anything that changes the direction and intensity of magnetic field induces eddy current in conductor.”
The value of current induces is directly proportional to loop area, magnetic field strength and rate of change of flux while inversely proportional to the material resistivity.
How does eddy current produce?
As we know that in magnetic field, charged particles experience a force. There are so many free electrons in conductive materials that move around within the material. As these electron’s experiences a force due to change of magnetic flux within magnetic field, creates circular electric field perpendicular to that magnetic field. This electric field produces a flow of current in small loop, which is eddy current.
What does eddy current do?
Lenz’s law states that, as the induced eddy current flows, it will originate its own magnetic field. The direction of this magnetic field will be such that it opposes the external magnetic field. Thus, eddy current reduces the overall magnetic field. This property of reducing overall magnetic field is useful for stopping rotating power tools. Thus, eddy current causes energy loss in alternating current operating machinery.
Limiting eddy current
Metallic conductors are sliced into thin metal sheets to reduce eddy current. This reduces the surface area of conductor resulting in lowering eddy current loss. This phenomenon is adopt in transformer manufacturing world widely. Transformer cores are cut into thin sheets. These sheets are then laminated with insulator in between them to limit induced magnetic field. Thus result in limiting transformer iron core loss and heating loss.
Application of eddy current
- Eddy current also has advantages up to some extinct. It can be useful to diagnose cracks within the conductors. Since cracks within conductive material prevents formation of loops in that region thus resulting in detecting defects in materials. This is called nondestructive testing (NDT) and is often use to test airplane surfaces.
- It can be useful for braking purposes. As mentioned above, it can be helpful in quickly turning kinetic energy into other form of energy.
- Another application of eddy current is its use in certain type of proximity sensors to observe the vibration and function of rotating shafts inside their bearings. Those sensors are extremely sensitive to very small displacements making them well suitable to examine the minute vibrations in turbo-machinery.
- It can also be useful for the identification of coins. The coin rolls beyond a stationary magnet, and eddy currents slow its pace. The eddy currents strength and thus the retardation, relies upon at the conductivity of the coin’s metal. Slug coins behave differently than genuine coins.
Eddy current is also responsible for skin effect in high voltage conductors.
To read more about skin effect follow the below given article.
|What is skin effect in electrical power system?|