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Remanent magnetic flux

Discussion in 'General Electronics Discussion' started by Asj, Jan 24, 2012.

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  1. Asj

    Asj

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    Jan 23, 2012
    Remenanent flux in core of transformer is to be given path to collapse in neutral . how this can be done before application of next DC pulse .
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,309
    2,238
    Nov 17, 2011
    Remanence or residual magnetism is a property of the material. It is not fundamentally linked to DC. It means that the core remains magnetized even after the magnetizing current has dropped to zero. This will happen even with AC current if the current is interrupted e.g. during zero crossing.
    You can either use core material with a very low remanence or you can apply an AC current with steadily decreasing amplitude to minimize the hysteresis loop.

    See here http://hyperphysics.phy-astr.gsu.edu/hbase/solids/hyst.html for more

    Harald
     
  3. Asj

    Asj

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    Jan 23, 2012
    Since the core is getting magnetised in my case due to Pulse DC i have linked it with DC . Say i have applied 50msec pulse , core may have or may not have magnetised .But to avoid and mshap, i take precuation to demagnetise the core.after evry pulse is applied .nad making it ready for next pulse , this will avoid inrush current i may face later on. which my source may not be ready for.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,309
    2,238
    Nov 17, 2011
    Asy,
    it doesnt't matter where the magnetization comes from, whether AC, DC pulsed ...
    To demagnetize the core you'd have to use suitable material or a demagnetizing current.
    It is probably easier to limit the inrush current by a resistor or a suitably controlled transistor. The latter could be part of the oitput stage of your pulse generator. You'd limit the slew rate of the current by soft-switching the output transistor(s).

    Harald
     
  5. Asj

    Asj

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    Jan 23, 2012
    Ckt analysis of the attachment

    Can any one analyse the ckt attached .
     

    Attached Files:

  6. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Study the hysteresis curves - for example here, here, here, here, and here.

    You'll see that it requires a very precisely controlled current in the opposite direction to demagnetize it. The exact value depends on the first magnetizing level.
    Magnetizing the core in the opposite direction would be at least as beneficial, and would simply require a large pulse in the opposite direction.

    All of this is of no importance to ferrite cores since they have almost no remanence.
    For iron cores it may matter, and you may even need to apply a decaying AC to be able to return it to the virgin curve (if that's the property you need from it).
     
  7. Asj

    Asj

    10
    0
    Jan 23, 2012
    remeanent flux removal

    Can burst of pulses will help in demagnetising the core.?
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    10,309
    2,238
    Nov 17, 2011
    Asj,
    no, it is neither the frequency nor the number of pulses that demagnetizes a core. It is the decaying magnitude.
     
  9. Asj

    Asj

    10
    0
    Jan 23, 2012
    remeanent flux removal

    Can i remove the remanent flux using RC snubber at output of switch
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    10,309
    2,238
    Nov 17, 2011
    No, you can't.
    The RC snubber will attenuate the voltage spike when switching the current through the coil. It will not generate a demagnetizing current.
    As Resqueline already stated: use a ferrite core to minimize remanence.

    Harald
     
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