Re: Problem with FEMM

["emiliano.menghi@xxxxxxxxx" <emiliano.menghi@xxxxxxxxx>]

--- In femm@xxxxxxxxxxxxxxx, "David Meeker <dcm3c@xxxx>" <dcm3c@xxxx> wrote:

> --- In femm@xxxxxxxxxxxxxxx, "zifera <emiliano.menghi@xxxx>"

> <emiliano.menghi@xxxx> wrote:

> > Dear David and Femm users, i've a big problem with Femm and i hope 

> > that you want help me.

> > I use FEMM to computate the shielding effectiveness (low frequency: 

> > 50-60 hetz) of plane aluminium screen (tickness 3 mm, lenght 2 m). 

> > The source is a triphase cable system with simmtric current (500 A). 

> > The distance between the conductor is 25 cm. The position of the 

> > screen is simmetric respect the conductors (the conductors are in 

> > plane) 

> > The problem is that near the screen the magnetic field (calculated 

> > along a line parallel to the sceen) is not simmetric!! For distance 

> > bigger than 50 cm magnetic field return to be simmetric. Why?

> > I've tested the same configuration with a commercial fem (Ansoft) and 

> > the result is equal.

> > Thanks.

> > 

> > Emiliano

> 

> If I understand your geometry correctly, I don't think that the field

> distribution here should be symmetric. Essentially, if you've put

> three-phase conductors in a line on top of a plate, you've made

> yourself a linear induction motor. A wave of flux travels from one

> side of the plate to another, and you can get a funny looking total

> field when you include the reaction field from the plate.

> 

> When viewed from far away, the combined field of the three wires in a

> row begins to look like that of a dipole whose strength varies

> sinusoidally with respect to time. The field then looks a lot more

> regular.

> 

> Dave.





I send you an example of the configuration.

In this case the screen thickness is 3 mm and the lenght is 1 m

You can plot B along the line (-200, -100; 200, -100)

Bye

[Format]      =  3.0
[Frequency]   =  50
[Precision]   =  1e-008
[LengthUnits] =  centimeters
[ProblemType] =  planar
[Coordinates] =  cartesian
[Comment]     =  "Add comments here."
[PointProps]   = 0
[BdryProps]   = 1
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    <BdryName> = "Boundary"
    <BdryType> = 0
    <A_0> = 0
    <A_1> = 0
    <A_2> = 0
    <Phi> = 0
    <c0> = 0
    <c1> = 0
    <Mu_ssd> = 0
    <Sigma_ssd> = 0
  <EndBdry>
[BlockProps]  = 4
  <BeginBlock>
    <BlockName> = "Copper"
    <Mu_x> = 1
    <Mu_y> = 1
    <H_c> = 0
    <H_cAngle> = 0
    <J_re> = 0
    <J_im> = 0
    <Sigma> = 58
    <d_lam> = 0
    <Phi_h> = 0
    <LamType> = 0
    <LamFill> = 1
    <BHPoints> = 0
  <EndBlock>
  <BeginBlock>
    <BlockName> = "Air"
    <Mu_x> = 1
    <Mu_y> = 1
    <H_c> = 0
    <H_cAngle> = 0
    <J_re> = 0
    <J_im> = 0
    <Sigma> = 0
    <d_lam> = 0
    <Phi_h> = 0
    <LamType> = 0
    <LamFill> = 1
    <BHPoints> = 0
  <EndBlock>
  <BeginBlock>
    <BlockName> = "Lead Alloy"
    <Mu_x> = 1
    <Mu_y> = 1
    <H_c> = 0
    <H_cAngle> = 0
    <J_re> = 0
    <J_im> = 0
    <Sigma> = 4.6699999999999999
    <d_lam> = 0
    <Phi_h> = 0
    <LamType> = 0
    <LamFill> = 1
    <BHPoints> = 0
  <EndBlock>
  <BeginBlock>
    <BlockName> = "Earth"
    <Mu_x> = 1
    <Mu_y> = 1
    <H_c> = 0
    <H_cAngle> = 0
    <J_re> = 0
    <J_im> = 0
    <Sigma> = 1e-008
    <d_lam> = 0
    <Phi_h> = 0
    <LamType> = 0
    <LamFill> = 1
    <BHPoints> = 0
  <EndBlock>
[CircuitProps]  = 4
  <BeginCircuit>
    <CircuitName> = "phase R"
    <VoltGradient_re> = 0
    <VoltGradient_im> = 0
    <TotalAmps_re> = 400
    <TotalAmps_im> = 0
    <CircuitType> = 0
  <EndCircuit>
  <BeginCircuit>
    <CircuitName> = "Phase S"
    <VoltGradient_re> = 0
    <VoltGradient_im> = 0
    <TotalAmps_re> = -200
    <TotalAmps_im> = -346.41016000000002
    <CircuitType> = 0
  <EndCircuit>
  <BeginCircuit>
    <CircuitName> = "Phase T"
    <VoltGradient_re> = 0
    <VoltGradient_im> = 0
    <TotalAmps_re> = -200
    <TotalAmps_im> = 346.41016000000002
    <CircuitType> = 0
  <EndCircuit>
  <BeginCircuit>
    <CircuitName> = "zeroo"
    <VoltGradient_re> = 0
    <VoltGradient_im> = 0
    <TotalAmps_re> = 0
    <TotalAmps_im> = 0
    <CircuitType> = 0
  <EndCircuit>
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-1.919999999999999	-145	0	0
4.1500000000000004	-145	0	0
-4.1500000000000004	-145	0	0
29.149999999999999	-145	0	0
20.850000000000001	-145	0	0
26.920000000000002	-145	0	0
23.079999999999998	-145	0	0
-20.850000000000001	-145	0	0
-29.149999999999999	-145	0	0
-23.079999999999998	-145	0	0
-26.920000000000002	-145	0	0
-100	-145	0	0
100	-145	0	0
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-500	-145	0	0
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-1500	-145	0	0
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2000	-145	0	0
-50	-135	0	0
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-50	-135.30000000000001	0	0
50	-135.30000000000001	0	0
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800	-145	0	0
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55	-183	2	3	0	0	0
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35.399999999999999	-135.19999999999999	1	0.080000000000000002	4	0	0
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