Experimental Assessment and Modeling of Losses in Interlocked Magnetic Cores

The use of interlocks often represents an affordable stacking solution for soft magnetic cores in mass production of electrical machines. However, due to the process itself, the material behavior and thus the resulting electrical machine performance is negatively impacted. On the one hand, this is due to additional conductive paths, which increase the eddy current losses. On the other hand, locally introduced mechanical stresses occur. These lead to nonnegligible degradation of the magnetic material properties inside and around the interlock area, following higher hysteresis losses. This article investigates and develops a reliable and accurate three-dimensional finite-element method model that considers the contact resistance between interlocks and laminations, as well as layered regions for the material degradation around the interlock area. Examples of flux and eddy current density distributions are provided, together with the computation of the total iron losses for a variable number of rectangular dowels in the yoke of stator core samples. The numerical analyses are validated by several interlaboratory measurements conducted on multiple stator core samples made of two different grades of electrical steels and with different numbers of interlocks. Results reveal impact of some percent on the core losses and well evident degradation on the material BH curve.