EDDY CURRENT AND APPLICATIONS PROJECT

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Basic Structure of Eddy Current Brakes

Eddy current brakes basically consist of a rotating disc (made of conductive material) and apermanent magnet:

As the disc spins in the constant magnetic field generated by the permanent magnet, 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 befound in cars as !ell.

$ou may have also heard 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 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 doesnot move !ith the rotating disc it stays !here the magnet is located.

Note that the induced Lorentz current density term often leads to confusion when modeling

electromagnetics where 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 movingsources generate magnetic flux that cannot be included in the 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 aninitial 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, you can figure out ho! much tor&ue your brake system !ill have. 3hat#s
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notable is that you can include the rotation of the device !ithout having a moving mesh. The

magnetic brake modelcouples 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 tocompletely brake the system.

3D model showing induced eddy currentdensity and direction at t! s.

3D model showing induced eddy currentdensity 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 electricitywhich 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.
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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.


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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


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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 eddycurrents 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.


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Arrangement of &'( in high speed trains)

&'( I* 'A+S)


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Sources)

https),,www.youtube.com,watch?v-otu/01iH2I

https),,www.youtube.com,watch?v-mopfu0feIhc

https),,www.youtube.com,watch?v-ek3k*245k3k

EDDY CURRENT AND APPLICATIONS PROJECT

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