Development of Methods for Measuring Magnetic Characteristics of Strong Magnet

对IEC标准《强磁体磁特性测量方法》草案的编制进行了基础性研究。主要研究结果如下：1.考虑磁滞特性的无取向材料磁场分析方法的发展为了计算永磁体的退磁因子，发展了考虑磁滞特性的无取向材料磁场分析方法。该方法以M-B回线作为磁特性，并假设磁化方向与磁通密度方向相同.电容器放电励磁电机磁场分析方法的发展在开路磁路法脉冲宽度较小时，涡流产生的反向磁场对磁场强度的测量误差是不可忽略的。为了研究脉冲宽度对测量精度的影响，提出了磁化电流未知的有限元法。通过计算结果与实测结果的对比，验证了该方法的有效性.影响测量精度的因素（1）磁体形状从退磁系数恒定的角度考虑，磁体的最佳形状为磁体的高度与直径相同。(2)Nd-Fe-B磁体的退磁因子在矫顽力附近的变化幅度大于Sm-Co磁体。(3)试样侧面的制造劣化对退磁因子的影响大于边缘面。当试样较长时，这种影响较大。(4)涡流脉冲磁铁产生的磁场变化dB/dt应小于80 T/ms，以获得3%的精度。

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.