[W-MA-47] Toward Practical Application of Iron Loss Analysis Taking Stress into Account

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1. Environments That Take Stress into Account

Increasing the accuracy of an iron loss analysis for a magnetic field analysis poses challenges. With conventional iron loss calculation methods, the iron loss characteristics of electromagnetic steel sheet materials that were measured beforehand with methods such as the Epstein method are used to estimate iron loss in machines. However, it is known that iron loss increases more in electromagnetic steel sheets inside actual electric machines than it does than from various factors [1]. Stress can be cited as one of the factors. In figure 1, an example shows how iron loss in an electromagnetic steel sheet is affected by stress. Electromagnetic steel sheets in physical machines receive stress due to shrink fitting / press fitting the frame, fixed lamination from caulking / welding / bolt tightening, and temperature distribution (thermal stress). For example, the results of performing a structural analysis on compressive stress generated by press fitting the frame of a stator core in a motor is shown in figure 2. Compressive stress of 30 MPa or more is applied to the back yoke section, and the impact on iron loss is great when considering the rate of increase in figure 1. Therefore, it becomes clear that this factor cannot be ignored. The effects of stress must be accounted for in order to perform a highly reliable loss evaluation.

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