Development of Methods for Measuring Magnetic Characteristics of Strong Magnet

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The basic investigations for preparing the draft about IEC standard method of for measuring magnetic characteristic of strong magnet are carried out. The results obtained can be summarized as follows :1. Development of Method for Analyzing Magnetic Field in Non-Oriented Materials Taking into Account Hysteresis CharacteristicsIn order to calculate demagnetizing factor for permanent magnet, the method for analyzing magnetic field in non-oriented materials taking into account hysteresischaracteristics is developed. In this method, M-B loop is used as magnetic characteristics and the direction of magnetization is assumed to be the same with that of flux density.2. Development of Method for Analyzing Magnetic Field in Electric Machine Magnetized by Discharging Current of CapacitorsIf the pulse width of the open magnetic circuit method is small, the error of measured magnetic field strength due to the opposing magnetic field produced by he eddy current is not negligible. In order to investigate the effect of the pulse width on the accuracy, the finite element method, in which the magnetizing current is unknown, is developed. The validity of the method is verified by comparing the calculated results with measured ones.3. Factors Affecting Accuracy of Measurement(1) Shape of specimenThe optimum shape of specimen is that the height of magnet is the same with the diameter from a standpoint of constant demagnetizing factor.(2) Magnetic characteristics of specimenThe variation of demagnetizing factor of Nd-Fe-B magnet is larger than that of Sm-Co magnet near the coercive force.(3) Manufacturing deterioratrationThe effects of manufacturing deterioratin of side surface of specimen on the demagnetizing factor is larger than that of edge surface. This effects is large when the specimen is long.(4) Eddy currentThe change of magnetic field dB/dt produced by the pulse magnet should be less than 80T/ms in order to obtain 3% accuracy.