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EMI - induced current on two parallel wire

  1. Dec 8, 2008 #1
    I would like to quantify the EMI on a circuit and I am confused on how to do that. I have two parallel wires that are laying on top of each other. I have tried to calculate the flux linkage and came up with:

    [tex]\Lambda[/tex] = [l*[tex]\mu[/tex]o*I/(2pi)]*ln((d-a)/a)

    where a=radius of each wire, d=distance between the center of the wires, l=length of the wires, I=current on wire 1, and [tex]\mu[/tex]o*=permeability of free space.

    I don't understand how this would induce a current on wire 2 though.

    I'd really appreciate any help with this issue.

  2. jcsd
  3. Dec 8, 2008 #2
    A constant current will not induce a current in another wire; induced current is proportional to the change in the original current.
  4. Dec 9, 2008 #3
    Thank you for your reply. You are right. I'm sorry I forgot to indicate that the problem is occuring because inrush current. So, there would be a change in current. Do you know how to calculate the change in current on wire 2 due to a change in current on wire 1?
  5. Dec 9, 2008 #4


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    Homework Helper

    It depends on how exactly the current is changing. You don't necessarily need a change in current; a change in magnetic flux through some pre-defined surface or where magnetic flux lines are being cut suffices as well.
  6. Dec 9, 2008 #5
    If I could measure exactly how the current is changing on wire 1 do you know how I would be able to calculate the change in current on wire 2? Does the flux linkage equation apply here? If so, how does it translate into a change in current on wire 2?

  7. Dec 9, 2008 #6


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    Homework Helper

    You have to use Faraday's law here:
    [tex]Emf = -\frac{d\Phi_B}{dt} [/tex].
    So this gives you the induced emf on wire 2. To get the induced current, divide emf by resistance of wire 2. That's all I can say if you don't provide any more information on the setup.
  8. Dec 9, 2008 #7


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    Staff: Mentor

    You can have both inductive and capacitive crosstalk. The capacitive crosstalk is just coupling from wire-to-wire. Inductive coupling requires tso loops to couple the energy. So don't ignore the return paths of the wires in your inductive crosstalk calculation.
  9. Dec 11, 2008 #8
    thanks for the responses.
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