Basic Structure of Eddy Current Brakes Eddy current brakes basically consist of a rotating disc ( made of conductive material) and a permanent magnet:
As the disc spins in the constant magnetic field generated by the permanent magnet, magne t, its conductive properties induce eddy currents. The Lorent forces from these currents in turn slo! do!n the disc. The most common application areas of magnetic brakes are trains, roller coasters, and aircraft. "t#s not unlikely that eddy current brakes !ill eventually be found in cars as !ell. !ell. $ou $ou may have also heard he ard of electromagnetic brakes, !hich are similar in design, e%cept instead of a permanent magnet they have iron !ound !ith a coil.
Modeling Eddy Current Brakes Let#s suppose suppose you are designing an eddy current brake, and you !ant to kno! ho! large the permanent magnet needs to be in order to provide enough tor&ue to slo! do!n the vehicle (train, roller coaster, car') in time. "n this case !e#re assuming the induced current distribution does not move !ith the rotating disc it stays !here the magnet is located. Note that the induced Lorentz current current density term often leads to confusion when modeling electromagnetics where there there are moving magnetic sources or the moving domain is of bounded extent in the same direction as the motion or varies in this direction. These types of moving sources generate magnetic flux that cannot be included in the Lorentz Lorentz term. To be clear, in our case the induced current distribution is stationary and does not move with the disc. Let#s assume you have a copper disc that#s cm thick, has a radius of * cm, and moves at an initial angular speed of ,*** rpm. The T permanent magnet is connected via an iron yoke, and there#s a .+ cm gap of air !here the disc can spin. sing -/0L /ultiphysics and the A-12- /odule, /odule, you can figure out ou t ho! much tor&ue your brake b rake system !ill have. 3hat#s
notable is that you can include the rotation of the device !ithout having a moving mesh. The magnetic brake model couples a dynamic e&uation (this defines the rotation of the disc) !ith the finite element method (this defines the tor&ue). This !ill allo! you to calculate the total time to completely brake the system.
3D model showing induced eddy current density and direction at t! s.
3D model showing induced eddy current density and direction at t"# s.
$ou can also plot the time evolution of the angular velocity, braking tor&ue, and dissipated po!er in your magnetic brake system: CIRCULAR EDDY CURRENT BRAKING SYSTEM
metal discs (rotors) are connected to a rotating coil, and a magnetic feld between the rotor and the coil creates a current used to generate electricity which produces heat.
When electromagnets are used, control o the braking action is made possible by varying the strength o the magnetic feld.
The movement o the metal through the magnetic feld o the electromagnets creates eddy currents in the discs.
These eddy currents generate an opposing magnetic feld (Len!s law), which then resists the rotation o the discs, providing braking orce which decelerate the moving system.
The net result is to convert the motion o the rotors into heat in the rotors.
Linear eddy current brakes
"t is frst described by #rench physicist #oucault.
The linear eddy current brake consists o a magnetic yoke with electrical coils positioned along the rail, which are being magnetied alternating as south and north magnetic poles.
This magnet does not touch the rail, as with the magnetic brake, but is held at a constant small distance rom the rail (appro$imately seven mm).
When the magnet is moved along the rail, it generates a non%stationary magnetic feld in the head o the rail, which then generates electrical tension (#araday!s induction law), and causes eddy currents. These disturb the magnetic feld in such a way that the magnetic orce is diverted to the opposite o the direction o the movement, thus creating a horiontal orce component, which works against the movement o the magnet.
Advantages. . .
"ndependent o wheel&rail adhesion.
'o contact, thereore no wear or tear.
'o noise or smell.
dustable brake orce.
*igh brake orces at high speeds.
+sed also as service brake.
"t uses electromagnetic orce and not riction 'on%mechanical (no moving parts, no riction) an be activated at will via electrical signal Low maintenance Light weight
How does an eddy current brake stop something moving?
Suppose we have a huge solid block of copper mounted on wheels. It is moving at a very high speed and we need to stop it. Suppose we place a giant magnet next to the track so that train had to pass nearby. As the copper approached the magnet eddy currents would be generated inside the copper which would their own magnetic eld. As the front part approached the magnet eddy currents in that bit of copper would try to generate a repulsive magnetic eld to slow down copper!s approach to magnet. As the front passed by" slowing down" the currents there would reverse" generating an attractive magnetic eld that tried to pull the train back again. #again" slowing it down$. %he copper would heat up the eddy currents swirled inside it" gaining the kinetic energy lost by the train as it slowed down.
Arrangement of &'( in high speed trains)
&'( I* 'A+S)
Sources) https),,www.youtube.com,watch?v-otu/01iH2I https),,www.youtube.com,watch?v-mopfu0feIhc https),,www.youtube.com,watch?v-ek3k*245k3k
