Influence of Compressive Stresses on Core Losses and Magnetization Demand of Electrical Steel Sheets and Press Fitted Stator Cores

This paper illustrates the influence of compressive stresses up to – 175 MPa on the specific core losses and magnetization demand of electrical steel sheets and press-fitted stator cores. Therefore, the press fit of a real motor geometry is designed and the mechanical stresses occurring were calculated numerically at ambient and operating temperature. Furthermore, measurements are done with a single sheet tester under compressive stresses and press fitted stator cores as ring probes. Tests are done with electrical steel sheets made of M270-50A grade at different frequencies, taking into account applications for industrial drives. With rising compressive stress, magnetization demand rises clearly in medium polarization range up to 1500 % at −175 MPa compared to stress-free condition. Specific core losses increase continuously with rising compressive stress, and real geometry stator core results can partially be directly compared to strip probes under compressive stress. For specific core losses a loss separation is done by the Bertotti approach, separating specific hysteresis, specific eddy current and specific excess losses. The results get prepared to be used in modified finite element analysis (FEA) calculations of an electrical machine, taking into account the manufacturing step of press fitting.