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Eddy Currents and Induction Braking

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Eddy Currents and Induction ... The drag effects give rise to induction braking Absent external potentials will result in the system coming to a halt Heating ... – PowerPoint PPT presentation

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Title: Eddy Currents and Induction Braking


1
Eddy Currents and Induction Braking
  • By John Norris
  • Date Oct. 22, 2012

2
What is Induction?
  • Faradays Law
  • The induced electromotive force in any closed
    circuit is equal to the negative of the time rate
    of change of the magnetic flux through the
    circuit.
  • Lenzs Law
  • Why circuits obey Newtons third law along with
    the conservation of energy
  • An induced electromotive force (emf) always
    gives rise to a current whose magnetic field
    opposes the original change in magnetic flux

3
Induction Currents Eddy Currents
  • Called Eddy since they are analogous to fluid
    eddies in formation and behavior
  • Responsible for the opposing magnetic fields that
    produce drag and heating effects
  • The drag effects give rise to induction braking
  • Absent external potentials will result in the
    system coming to a halt
  • Heating effects are exploited by devices such as
    induction cookers
  • If left unchecked, then it could result in
    serious damage to mechanical/circuit components

4
Check on Heat Effects
  • High voltage circuits are constructed as a series
    of laminations to reduce eddy currents
  • Solid conductors would suffer increased
    resistivity and large energy losses (heat)

5
Drag Effects Magnetic Braking
  • Not to be confused with stellar magnetic braking
  • The primary reason for slow stellar rotations
  • Utilized in many practical applications
  • Trains (Maglev and conventional) as a braking
    system
  • Some roller coasters
  • Braking Industrial equipment and power tools
  • Some exercise equipment
  • Rowing or Spin machines to increase resistance
  • Determining structural defects in conductive
    materials
  • Metal Detectors

6
Circular vs. Linear
  • Metal disc, on the end of a rotor assembly,
    placed between two electromagnets
  • Static bank of magnets/conductors located on the
    tracks with conductors/magnets on the car

7
Advantages Disadvantages
  • Quiet
  • Almost no wear
  • Wear only if coolant system failure
  • Essentially zero maintenance
  • Produce no chemical pollution
  • Dust
  • Smell
  • Physical waste
  • No toxic chemicals
  • Need conventional brakes to hold a vehicle
    stationary
  • In reality certain sections of railroad tracks
    have lots of brake activity
  • Excess heat would cause structural issues
  • Reduce brake effectiveness
  • Increased cost

8
Regenerative Braking
  • Still not widely used
  • Basic idea has been around since the industrial
    revolution
  • Flywheels (mechanical capacitor)
  • Flywheels still used, but eddy currents can be
    exploited for this end as well
  • Capture the energy from the induced currents
    instead of it just being allowed to dissipate as
    heat
  • Avoids problem of having to carry around big
    flywheels

9
Demonstration
  • Copper pipe Neodymium magnets
  • Pipe Dimensions
  • ½ and ¾ diameter (outer) pipes both 1/32
    thick
  • Magnets (NdFeB)
  • ½ diameter
  • N42 Axially magnetized
  • Pull Force 3.1 lbs
  • Surface Field 1601 Gauss (0.1601 T)
  • Magnets have been weakened due to an living an
    abused life
  • For increase braking effect
  • More powerful magnet
  • Thicker contiguous pipe
  • Use more strongly conductive diamagnetic material
  • Lower temperature (pipe not magnet)

10
Great Videos
  • Liquid N2 and copper tube magnetic levitation
  • http//www.youtube.com/watch?vAzOSYJmYLTgfeature
    watch_response
  • Induction heater levitation molten aluminum
  • http//www.youtube.com/watch?vQ6Zrnv4OtbUfeature
    related
  • Worlds Strongest Magnet
  • Shot in the MagLab
  • http//www.youtube.com/watch?vQGytW_C6hR8feature
    watch-vrec

11
References
  1. "Diamagnetism." Wikipedia. Wikimedia Foundation,
    16 Oct. 2012. Web. 19 Oct. 2012.
    lthttp//en.wikipedia.org/wiki/Diamagnetismgt.
  2. "Eddy Current Brake." Wikipedia. Wikimedia
    Foundation, 10 Nov. 2012. Web. 19 Oct. 2012.
    lthttp//en.wikipedia.org/wiki/Eddy_current_brakegt
    .
  3. "Eddy Current Brakes." How Do Eddy-current Brakes
    Work? A Simple Introduction. N.p., n.d. Web. 19
    Oct. 2012. lthttp//www.explainthatstuff.com/eddy-
    current-brakes.htmlgt.
  4. "Eddy Current." Wikipedia. Wikimedia Foundation,
    16 Oct. 2012. Web.19 Oct. 2012.
    lthttp//en.wikipedia.org/wiki/Eddy_currentgt.
  5. "Faraday's Law of Induction." Wikipedia.
    Wikimedia Foundation, 17 Oct. 2012. Web. 19 Oct.
    2012. lthttp//en.wikipedia.org/wiki/Faraday's_law
    _of_inductiongt.
  6. "Lenz's Law." Wikipedia. Wikimedia Foundation, 16
    Oct. 2012. Web. 19 Oct. 2012. lthttp//en.wikipedi
    a.org/wiki/Lenz's_lawgt.
  7. Neodymium Disk Magnets" KJ Magnetics. N.p.,
    n.d. Web. 19 Oct. 2012. lthttps//www.kjmagnetics.
    com/proddetail.asp?prodD81gt.
  8. "Regenerative Brakes." How Do Regenerative Brakes
    Work? N.p., n.d. Web. 19 Oct. 2012.
    lthttp//www.explainthatstuff.com/how- regenerative
    -brakes-work.htmlgt.

12
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17
Diamagnetism (wiKi)
  • Believed to be caused by the alteration of the
    electron orbital velocities
  • Alters magnetic dipole moment
  • Field will oppose the the magnetic field changes
    due to the external field
  • Caused by quantum mech (Landau Levels)
  • Copper Diamagnetic
  • Diamagnetism primarily responsible for the Lenz
    Law interaction
  • Superconductors completely repel external
    magnetic fields
  • All conductors exhibit an effective diamagnetism
    when they experience a changing magnetic field.
    The Lorentz force on electrons causes them to
    circulate around forming eddy currents. The eddy
    currents then produce an induced magnetic field
    which opposes the applied field, resisting the
    conductor's motion.
  • Joke Of course if I could have had some gold
    piping the effect could have been much stronger
    but I probably wouldnt have brought it to class
  • Magnetic permeability lt or 1
  • All conductors exhibit an effective diamagnetism
    when they experience a changing magnetic field.
    The Lorentz force on electrons causes them to
    circulate around forming eddy currents. The eddy
    currents then produce an induced magnetic field
    which opposes the applied field, resisting the
    conductor's motion.

18
Super Conductors
  • Pic Neodynium iron boron mags
  • What does 42 MGOe mean?
  • Mega Gauss Oersted magnetic energy product
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