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A train is a fantastic vehicle, and riding on one is a lot of fun. Do you recall seeing the trees as you boarded the train? Do you recall the loud screams that were heard prior to the train coming to a stop? What noise did you hear? Well, the train was being slowed down by a pilot. However, newer high-speed trains, monorails, and other types of trains do not hear this noise. . Why is that so? Everything concerning eddy currents will be covered in this article.
Eddy currents, often referred to as Foucault’s currents, are electrical current loops that are generated into conductors by a shifting magnetic field, in accordance with Faraday’s law of induction. When graphed, these circular currents within a metal object mimic eddies or whirlpools in a liquid. in this article we will learn more about them in-depth.
Have you noticed your car’s speedometer? A little low magnet in the speed indicator is attached to the car’s drive shaft. It rotates based on the vehicle’s speed. Eddy currents have the effect of opposing the rotational motion and deflecting the pointer at a specific angle. The calibrated scale and attached pointer show the vehicle’s speed.
Eddy currents waste energy because they tend to oppose one another. Many beneficial forms of energy, such as kinetic energy, are transformed into heat by eddy currents, which is typically not beneficial.
What is Eddy Current ? | eddy current definition?
Eddy currents are currents that move through conductors like the whirling eddies in a stream. They flow in closed loops perpendicular to the magnetic field’s plane and are produced by shifting magnetic fields. Eddy currents are caused by changes in the strength or direction of a magnetic field experienced by a conductor, which can happen when the conductor is travelling through a magnetic field or when the magnetic field around a stationary conductor is changing. The amount of the eddy current is inversely proportional to the conductor’s resistivity and directly related to the magnetic field’s strength, the loop’s area, and the rate at which the flux is changing. Eddy currents create their own magnetic fields just like any other current that flows through a conductor. According to Lenz’s Law, the magnetic field produced by a magnetically induced current, such as an eddy current, will oppose the change in magnetic field that caused it. Eddy current braking, a widely used technique for halting rotating power tools and rollercoasters, takes advantage of this resistance produced by the opposing magnetic fields.
Eddy currents are produced when ? | How are Eddy Currents Generated?
When a conductor moves through a magnetic field or when the magnetic field around a stationary conductor is altered, eddy currents are produced. As a result, anytime a conductor experiences a change in the strength or direction of a magnetic field, eddy currents may be produced.
Like swirling eddies in a stream, eddy currents move through conductors and are frequently created in reaction to a changing magnetic field. They are caused by shifting magnetic fields to flow in closed loops that are perpendicular to the magnetic field plane. Also known as Foucault’s Currents, these. Lenz’s Law states that the direction of an induced current will be similar to an eddy current in that the magnetic field it generates will oppose the change in the magnetic field that generated it. Within a conductor, this requires the motion of electrons in a plane perpendicular to the magnetic field. The eddy current’s strength is:
proportionate to the magnetic field’s strength
proportionate to the loop’s surface area
related to how quickly the magnetic flux changes
oppositely related to the resistivity
Eddy current results in energy loss in a conductor because it has a tendency to oppose changes in the magnetic field that produce it. devices convert electrical or kinetic energy—two types of energy—into heat. We use the resistance produced by the opposing magnetic field to generate eddy currents for braking in order to stop rotating power tools and rollercoasters.
Eddy currents were originally observed in 1824 by François Arago, the 25th Prime Minister of France and a mathematician, scientist, and astronomer. 1824. He was the first to see the rotational magnetism, and he understood that most conductive items could be made magnetic. Ten years later, Heinrich Lenz published the Lenz law, but it wasn’t until 1855 that Léon Foucault, a French physicist, made the formal discovery of eddy currents. He conducted several experiments and came to the conclusion that when the rim of a copper disc is placed between the poles of a magnet, the force required to rotate it increases ( like a horseshoe magnet). The disc heated up as a result of these induced eddy currents.
Properties of Eddy Currents:
eddy current has the following properties.
These only occur inside of conducting materials.
Defects like cracks, corrosion, sharp edges, etc. deform them.
The intensity of eddy currents increases at the surface and decreases with depth.
Applications of eddy current | Uses of eddy current:
there are lots of application of eddy current. some of them are as below.
Modern high-speed Maglev trains use this repulsive type of levitation to ensure frictionless transportation. Eddy currents are created on the stationary conducting sheet over which the train levitates by the shifting magnetic flux produced by a superconducting magnet mounted on the running train. Eddy currents and the magnetic field combine to create levitational forces.
Hyperthermia Cancer Treatment:
Eddy current heating is used for tissue heating during hyperthermia cancer treatment. proximal wire windings coupled to a capacitor to create a tank circuit, which is connected to a radio frequency source, cause eddy currents in the conducting tubings.
Eddy Current Braking:
Kinetic energy that is lost as heat owing to eddy current losses has a wide range of industrial uses, including:
Eddy currents are produced in the wheels when the brakes apply pressure, exposing the metal wheels to a magnetic field. The wheels are slowed down by the magnetic interaction between the applied field and the eddy currents. As the train slows, the braking force decreases, resulting in a gentle stopping action. The stronger the effect, the faster the wheels spin.
A roller coaster braking:
A series of strong, permanent magnets permanently install at the end of the track of a rollercoaster ride. As the cars speed by, these magnets create eddy currents in the metal components affixed on the sides of the vehicles. Up until the very end of the trip, the cars travel freely around the track before the brakes engage and the magnets collide with the metal.
Electric saw or drill for its shut-off in an emergency:
Eddy current is also used in electrical saw and drill for emergency stoppage.
Induction Heating | Induction furnace:
With the aid of a high frequency electromagnet and eddy currents, a conducting body is heated electrically through the process of induction heating. Its primary uses include induction cooking, melting metals in an induction furnace, welding, brazing, and other processes.
Large eddy currents are created in magnetic fields that are rapidly changing because of the strong emf that is produced. Temperature is created by eddy currents. As a result, a high temperature is produced. Therefore, a coil is wrapped around a constituent metal that is set in a magnetic field that is produced by a high frequency and is highly oscillating. The metal will melt at the generated temperature. Metals are extracted from ores using this method. By melting the metals in an induction furnace at a very high temperature, alloys can be created.
Eddy Current Adjustable Speed Drives:
An eddy current linked speed drive is possible with the aid of a feedback controller. It is used in plastic processing, conveyors, metal forging, etc.
Eddy current induction in the metal, if present, is used by metal detectors to identify the presence of metals in rocks, soils, and other materials.
Applications for data processing:
Eddy current non-destructive testing is used to examine the composition and toughness of metal constructions.
Deadbeat galvanometers are created via electromagnetic damping. Before the needle settles, it often oscillates a little bit around its equilibrium point. The coil is wound around a metallic frame that is not magnetic to prevent the delay in reading acquisition caused by this. As the coil is deflected, eddy currents form in the metallic frame, which causes the needle to come to rest very immediately. So, the “coil is dampened” in its motion. A fixed core of nonmagnetic metallic material is used in some galvanometers. Eddy currents produced in the coil’s core oppose the motion of the coil as it oscillates, bringing the coil to a stop.
Electric Power Meters:
Eddy currents cause the gleaming metal disc in the electric power metre to rotate. The electric currents in the disc are produced by the magnetic field. The gleaming disc can also be seen from your home.
These currents are used to determine a vehicle’s speed. A magnet that continuously rotates in accordance with the speed of our car makes up a speedometer. In the drum, eddy currents are generated. The pointer attached to the drum indicates the speed of the vehicle as the drum rotates in the direction of the magnet’s rotation.
Eddy current test:
eddy current test is used to detect the following..
- Crack detection: Equipment for detecting eddy current cracks can be categorised as high frequency instruments for ferrous and non-ferrous materials that have surface-breaking cracks and low frequency instruments for non-ferrous materials that have subterranean cracks.
- Tube and wiring testing: Eddy current test systems that can inspect tube, bar, and wire at 3 m/s have been developed. The test installation automatically starts when the operator calibrates the device using a tube or wire with known faults, removing flawed products from the production line or painting them with paint.
- Condenser tube inspection: The heat exchangers of pressurised water reactors are currently the focus of a lot of research on this application as eddy current testing is useful in this.
- Material sorting:The approach delivers a better sample of material qualities than many other material sorting methods, and more significantly, it is relatively quick since eddy current fields penetrate beyond the surface of the test material.
- Welding testing: Simple high frequency eddy current testers have been employed for some time to find toe fractures in ferrous welds. The technique has the benefit of being able to see flaws through multiple coats of paint. High noise levels brought on by weld permeability fluctuations and lift-off noise from rough cap surfaces are the drawbacks.
- Coating thickness measurement: Eddy current testing is effective for precisely measuring paint and metallic coatings on metal surfaces due to its excellent near-surface resolution.
Eddy Current loss | eddy current loss formula
Faraday’s Law of Electromagnetic Induction states that when magnetic material is exposed to a magnetic field produced by alternating current, an emf is inducted into the core material. The magnetic material has an electrically conductive quality, and the induced emf in the material induces current flow. Within the substance, the current moves around. And the EMF-generated circulation currents are known as eddy currents. Eddy current loss is the name given to the heat that is lost as a result of eddy currents in magnetic material.
Eddy Currents are the circulating current that the induced EMF causes. Eddy current loss refers to the heat loss resulting from eddy currents.
Hysteresis loss is the other loss in the magnetic substance. Iron loss, magnetic loss, and constant loss are the combined eddy current and hysteresis losses.
Alternating current creates magnetic flux in the magnetic material when it passes through the coil. Inducing EMF at multiple core sites, the flux also relates to the core material. The core’s closed-loop circulation current is caused by the potential difference. Eddy Current is the name of the circulating current.
The eddy current loss proportional to;
The eddy current’s square (I2)
Resistance of the core (R)
Thus formula of eddy current losses is Eddy Current loss (We) = K x I2 R (Where K is the eddy current constant)
How to Reduce Eddy Current Loss?
By lowering the current, we can lower the eddy current loss. As core resistance rises, the current declines. The core resistance can be reduced via;
using flimsy laminated sheets in the core
using silicon steel with a high resistivity as the core material
Thin laminated sheets are used to create the core. Electrical insulation is provided between two adjacent sheet
s by the lamination on the sheets. The thin sheet’s resistance is higher because its cross-sectional area is less (R = ρL/A). Eddy currents are hampered by the high resistance. As a result, current and loss are reduced in size.
The use of a CRGO (Cold Rolled Grain Oriented) Steel core is the alternative technique for decreasing current and loss. Due to the greater electrical resistance of the CRGO steel core, the loss is decreased.
Eddy current loss in transformer:
According to the faraday law and the lenz law, the magnetic field flow inside the transformer core causes emf in the core, causing eddy current to flow as illustrated in the picture below. Take a look at the transformer core part in the illustration. Eddy current ieddy circulates inside the core as a result of the magnetic field B(t) created by the winding current i(t).
Eddy current losses can be expressed as follows:
Where f is the frequency of the excitation source, Bm is the peak value of the magnetic field, and T is the thickness of the material, ke is a constant that depends on the size and is inversely proportional to the material’s resistivity.
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