Measurement and Analysis of AC Loss of NdFeB Sintered Magnet

NdFeB sintered magnets are widely used in rotating machines. As the conductivity of NdFeB sintered magnet is fairly high compared with that of ferrite magnet, the eddy current loss due to slot ripple etc. cannot be neglected. If the eddy current loss of permanent magnet becomes large, the temperature of permanent magnet becomes high and the thermal demagnetization becomes serious. Therefore, it is required to evaluate ac loss of permanent magnet. But the measurement of ac loss of permanent magnet under serious operating condition is not reported yet. In this paper, the ac loss of NdFeB sintered magnet was measured using newly developed closed-type measuring equipment. It is shown that the coaxial double coil is useful for accurate measurement of magnetic field. The eddy current loss and hysteresis loss of permanent magnet are obtained by the loss separation. It is illustrated that the hysteresis loss is larger than the eddy current loss in the range of less than several hundred Hertz. The appropriateness of measurement is verified by the numerical analysis.