LABORATORIO ELETTROFISICO YOUR MAGNETIC PARTNER SINCE 1959

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Evelina Di Lorenzo
8 anni fa
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1 FINITE ELEMENT ANALYSIS (F.E.A.) IN THE DESIGN OF MAGNETIZING COILS How does it works? the Customer s samples are needed! (0 days time) FEA calculation the Customer s drawings are of great help! (3 days time) mechanical drawing ready for assemblying prototyping coil! (10 days time) FEA calculation the coil is ready! (25 days time)

(0 days time) FEA calculation the Customer s drawings are of great help!

2 What is F.E.A.? Finite element analysis is the most popular numerical method for the solution of electromagnetic field problems: it is applied to a wide range of different applications and in the last two decades it lived a strong increase also in this electromagnetism. Laboratorio Elettrofisico has been using F.E.A. analysis for the design and optimization of its equipment since 1991, when, especially among companies producing measuring and automatic equipments, it was very unusual. Figure 1: meshing of 2D geometry (turn section in which electric current J is flowing) Figure 2: magnetic induction around the turn section.

applications and in the last two decades it lived a strong increase also in this electromagnetism. Laboratorio Elettrofisico has been using F.E.A.

3 Why using F.E.A. to design magnetizing coils? The final step of any electromagnetic design is an experimental prototype, to verify the electromagnetic, mechanical and thermal characteristics of the device: building up one or several can be sometimes very expensive, especially if the device has a unique and complex geometry. This is the case of most of Laboratorio Elettrofisico magnetizing and measuring devices, as most of rotors, stators or actuators to be magnetized or measured are different in magnetic properties or geometries from all the other ones. Furthermore only by mean of a computer analysis it is possible to obtain many different models of the device in a short time and to test very difficult solutions or too expensive to realize in an experimental prototype. Figure 3: radial magnetization of NdFeB bonded ring. Internal radius of the magnet was only 3 mm. Real magnetizing is very small but very complex to produce.

sometimes very expensive, especially if the device has a unique and complex geometry.

4 Transient electromagnetic and coupled analysis Most of the F.E.A. analysis in L.E. are performed to model very fast transitory phenomena, as magnetizing process are obtained by capacitors discharge in a magnetizing fixture.

5 Laboratorio Elettrofisico: using F.E.A. in magnetizing design Sometimes an estimation by analytical model (by classical circuit modelling) is possible, maybe together with the comparison of previous electric and magnetic results of similar previous device. But usually in magnetism is not easy to create reliable models by classic circuit magnetic, as you deal with non linear material, big flux leakage and sometimes also with Eddy currents effects. Such approach is almost impossible if you are dealing each time with new design of motors, sensors or actuators, what is usual in Laboratorio Elettrofisico: so each time classic circuit models should be studied, tested and approved, which is not possible giving answer in few days or hours! Actually, a realistic model can start only during the following steps: 2D model transient model, which can be performed also by the : parametrization of the geometry and energy optimization of the geometry and energy validation of the best solution 3D static and transient model o magnetic static analysis using current obtained in 2D transient analysis and, sometimes o parametrization of the geometry and energy o optimization of the geometry and energy o validation of the best solution

6 Final device production and test: comparison with F.E.A. prediction. Figure 4: two poles bitter coil (RAB model). Detail of the magnetizing field direction and distribution on a vertical section. Figure 5: rectangular bitter coil, 2 poles, air cooled.

Detail of the magnetizing field direction and distribution on

7 Figure 6: four poles - iron wound magnetizing fixture (CAF model). Figure 7: four poles - iron wound magnetizing fixture: detail of the mesh (CAF model)

8 Figure 8: example of CAF model coil (air cooled) and samples. Figure 9: HE multipolar fixtures for servomotors and generators and samples

9 Thermal analysis To obtain the minimum cycle time a thermal analysis is also possible: it is further more complex, as it requires a 3D simulation (due to the 3D effect of cooling fluid flow) and the convective exchange are also difficult to set. But the details you can get with F.E.M. analysis cannot be obtained with other method and this can be very useful as the high temperature area in magnetizing fixture are usually very localized in space (and transient are very short, too).

set. But the details you can get with F.E.M.

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