Magnetic Circuit Analysis /Reduction in Eddy Current by Splitting Magnets
As a countermeasure to eddy current, it is effective to split magnets. We further investigated split magnets. The eddy current loss was compared for a motor with magnets not split and with the magnets split into 6 pieces as in Figure (a). There were four test materials: C1020 copper, A7075 aluminum, SUS304 stainless steel, and N36UH magnets. The test pieces were 50x50x10 mm, the strength of the AC magnetic field was ±12.3 kA/m (±154 Oe) and the frequency was 2000 Hz.
Figure (b) shows the relationship of the eddy current loss with whether or not the magnets were split. With copper and aluminum, which have comparatively weak resistance, the loss is larger when the magnets are split. This is due to the surface effect of eddy current. When the test piece is larger or the frequency is high, the eddy loss due to splitting increases.
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Figure (a) Magnets split into 6 and not split
Figure (b) Comparison of eddy current loss
Figure (c) shows the result of bringing the split test material in contact without insulation and measuring the eddy current loss. A comparison was made with items completely insulated between layers. It was found that splitting had an effect for all the materials, regardless of the insulation between layers. When producing split magnets, there is no need for a process to completely insulate between layers, for example with paint.
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Figure (c) Relationship of the eddy current loss with whether or not the magnets are split
