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Impact of Shield Thickness on Reducing Stray Losses (T.E.A.M. Problem 21c)

Transformers with MagNet for SOLIDWORKS

The purpose of this family of benchmarks is to investigate the effects of shielding on flux densities outside of transformers. In this problem, there are two exciting coils directed in opposite directions and shielded by magnetic (M) or electromagnetic (EM) shields. The magnetic shields are made of anisotropic silicon steel sheets, and the electromagnetic shields are made of copper plates.

There are two types of shields in this benchmark: one single silicon steel sheet or copper plate (M1 or EM1), or three separated silicon steel sheets or plates (M2 or EM2). The transformer wall is made out of magnetic steel.

The magnetic field density is measured along contours on the surface of the transformer wall, and of the shields, and compared with measured results. The following example is based on the Testing Electromagnetic Analysis Methods (T.E.A.M.) problem #21c: 3-D Stray Field Loss. The benchmark can be found on the International Compumag Society's website.

Transformer with different shielding thickness

METHODS and RESULTS

MAGNETIC FLUX DENSITY in the TRANSFORMER WALL

The power source is sinusoidal and there are solid conductors present, therefore an AC Time Harmonic simulation is required. Shown here are plots of the magnetic flux density on the surface of the magnetic steel plate that is furthest away from the exciting coils.

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TOTAL LOSS in the TRANSFORMER WALL

Shown here is a plot of the total loss on the outer surface of the transformer wall for each of the four different configurations.

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EDDY CURRENTS

Displayed here are the arrow plots of current density inside the magnetic steel for the two configurations containing magnetic shields (P21-M1 and P21-M2). The arrows indicate direction while the colors indicate field intensity.

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ELECTROMAGNETIC SHIELD'S EFFECT ON EDDY CURRENTS

Shown here are the arrow plots of current density inside the magnetic steel for the two configurations containing electromagnetic shields (P21-EM1 and P21-EM2). The effect of the copper shielding on the field strengths inside the transformer wall can be seen clearly.

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FLUX DENSITY on the PLATE SURFACE

Comparing the flux density along a contour on the steel plate surface.

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ANISOTROPIC USER-DEFINED MATERIALS

In this example, P21c-M1 and P21c-M2 use laminated silicon steel sheets as a shielding material. Laminated silicon steel can be modeled by creating a material that has a non-linear, anisotropic magnetic permeability. Shown here are the B-H curves for the laminated silicon steel that were used in the example.

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COMPARING MAGNET for SOLIDWORKS & MEASURED RESULTS

In the description of TEAM Problem 21c, experimental values are given for the magnetic flux densities along contours on the surface of the shield and of the transformer wall. Displayed here is a graphical comparison between the results that were generated by MagNet for SOLIDWORKS simulation and the experimental data.

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