It was found out manually that for the magnetic flux density in the air-gap B=1,0T, the magneto-motive force required is Fw=968mA. For the same mmf Fw, the result obtained by FEMM, using magnetic material with the same quality as in Table 1, is B=0,942T. This is an average value. Actually the distribution of the flux density B along the pole face is not uniform, due to the fringing effect. In the central part of the pole B is less than at the pole edges. However the error of the manual calculations does not exceed 6%. In Fig. 2 based on the data taken from the FEMM solution, the picture of the fringing is depicted. The actual distribution of the flux density along the pole face (line C; A; Al; Cl) is presented in Fig. 3. It is worth mentioning that the distance between the corresponding points C; A and Al; Cl is 10 mm.
When the driving mmf is doubled Fw=1936 mA, the result obtained by FEMM is B=1,453T.
Fig. 2 - Magnetic field distribution in the magnetic circuit in fig. 1 based on computer-aided analyses by FEMM.
Fig. 3 - Distribution of the magnetic flux density B in the air-gap for the fig. 2 configuration.
Electromagnetic Module. Modelling, Analysis and Design.
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