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Eddy currents (also known as Foucault’s currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor, according to Faraday’s law of induction. Eddy currents flow in closed loops in planes perpendicular to the magnetic field within conductors. Eddy currents can be reduced by breaking the circuit and preventing current loops from circulating through cracks or slits in the conductor. As a result, Eddy currents can be used to detect flaws in materials. The term “nondestructive testing” is commonly used in the aviation industry. A change in the magnetic field produced by Eddy currents indicates the presence of an irregularity; a defect reduces the size of the Eddy current, lowering the magnetic field strength.
Another application of Eddy currents is magnetic levitation. Conductors are subjected to varying magnetic fields, which cause Eddy currents to form within the conductor and a repulsive magnetic field to form, pushing the magnet and conductor apart.
Electric power metres:
Eddy currents cause the shiny metal disc in the electric power metre (analogue type) to rotate. Magnetic fields produced by sinusoidally varying currents in a coil induce electric currents in the disc.
Electromagnetic Damping
When an Eddy current comes into close contact with a conductive or magnetic object, electromagnetic damping occurs. When an Eddy current interacts with another magnetic field, it produces a damping force (i.e., reduction in motion). Electromagnetic damping is a resistive force that causes a conductive or magnetic object in an Eddy current field to slow down without being touched.
The interaction between the Eddy current and conductive materials slows the train down without using physical brakes, which is a principle used in rail brakes to help high-speed rail carriages stop at specific points without the use of physical brakes. Another application is galvanometers, which are devices that measure small electrical currents. To compensate for the galvanometer’s deflections, Eddy currents can be used to bring the coil closer to equilibrium.
The deflections are usually read-only after the testing process, and the coil in use has come to a halt. At that point, the galvanometer is no longer at equilibrium, and the accuracy of the galvanometer can be determined.
Induction furnace
An electric furnace is a heating chamber that uses electricity as a heat source to melt and alloy metals and refractories at extremely high temperatures. Electricity heats the metal, which has no electrochemical effect on it.
An arc or induction furnace is the most common type of modern electric furnace. The resistance furnace, which uses the furnace charge (i.e., the material to be heated) as the resistance element, is still used to produce silicon carbide and electrolytic aluminium. The heat-producing current is introduced through electrodes buried in the metal in one type of resistance furnace. Heat can be generated by the resistance components that line the inside of the furnace.
Electric Power Metres
Eddy currents cause the gleaming metal disc of the electric power metre to rotate. The electric currents in the disc flow due to the magnetic field. You can see the gleaming disc in your own home.
Single-phase induction energy metres work based on two fundamental principles:
- An aluminium disc is rotated.
- A method of calculating and visualising the amount of energy used.
Applications of Eddy Currents
- Braking Mechanism in Trains
Trains have metal wheels, and metal wheels move on metal tracks. The metal wheels of the trains are exposed to a magnetic field when the brakes are applied, causing Eddy currents to form. This impact increases as the train speeds up, and as the train slows down, the braking force decreases, bringing the train to a smooth stop.
- Damping in Galvanometers
The galvanometer needle usually swings back and forth around its equilibrium point before coming to rest. The needle oscillation causes a noticeable delay in the reading being recorded. This delay can be avoided by using a coil-over non-magnetic metal frame. Eddy currents are generated in the metallic frame as the coil is deflected, bringing the needle to a quick stop. The coil’s velocity is slowed here.
- Speed Indicators in Cars
Every vehicle we use for transportation has a speedometer, which indicates how quickly the vehicle is moving at any given moment. It has a magnet that rotates in response to the vehicle’s speed. Within the drum, Eddy currents are generated, which cause the pointer attached to the drum to move over the size because it moves in the same direction as the rotating magnet, indicating the vehicle’s speed.
- Rides in Amusement Parks
Eddy currents are used as a brake system in amusement park rides, allowing for smoother and contactless stopping.
How can we Minimise Eddy Currents:
- Eddy currents will be reduced in a number of ways, including by laminating the metal core.
- Insulating materials should be used to separate the laminations of the metallic core, and the plane of the laminations should be parallel to the magnetic flux, to chop across the routes of Eddy currents. The Eddy currents are weaker as a result of this configuration. Heat loss is significantly reduced because the conversion of electricity to heat is proportional to the square of the electrical current strength.
Conclusion
Eddy currents circulate in conductors like swirling eddies in a stream and are frequently caused by a changing force field. As force fields change, they circulate in closed loops perpendicular to the magnetic field plane. Foucault’s Currents is another name for them. Eddy currents have a tendency to cancel out the change in the field of force that causes them, resulting in energy loss in a large conductor.
The magnitude of the Eddy current is determined by the size of the magnetic field, loop area, rate of change of magnetic flux, and is inversely proportional to the conductor’s resistivity. These can often be reduced by laminating the core and using high-resistivity magnetic materials.
