Yuhito Doi

Factors affecting eddy current losses of segmented Nd-Fe-B sintered magnets without insulation in large PM motors

In large permanent magnet motors, the permanent magnet in the motor is segmented into parts in order to reduce the eddy current loss in permanent magnet. It is reported that the insulation between sintered Nd-Fe-B magnets is possible only by contacting the segmented permanent magnets without insulation. But the mechanism for such a phenomenon has not been clear. We have already reported that the analysis considering the resistance of the contact part is possible by defining the contact resistance coefficient K. In this paper, the effects of number of segments of magnet, exciting frequency and contact resistance between magnets on the eddy current loss of the magnet are investigated.

Examination of eddy current in laminated core without insulation

Purpose – In the laminated core of transformer, motor, etc. each electrical steel sheet is usually insulated in order to reduce the eddy current loss. Raw steel sheets without insulation are sometimes used in a small core of electrical machines and electronic equipments, because the cost of iron core can be reduced if cheap steel sheets without insulation are used in the core. The purpose of the paper is to show how the contact resistance between sheets of laminated core affects the interlaminar eddy current and to show the criterion for judgment of the necessity of insulation. Design/methodology/approach – The eddy current losses of core made of SPCC (cold rolled steel sheets) of different widths with and without insulation under various conditions are analyzed by using the finite element method (FEM) considering the contact resistance. The equivalent circuit for such a laminated core without insulation is shown. The experimental investigation is also carried out. Findings – A criterion for the judgment ...