Calculation of Iron Loss with Stress in Stator Core by Shrinkage Tolerance

Abstract

This paper presents a method for calculating the iron loss of the stator core of an electric motor owing to the stress generated by shrink fit tolerance in the production process. Shrink fit is used to fix the frame and stator core, shaft, and rotor core in a motor, and the corresponding condition varies depending on the material. Three finite element analysis steps were performed to reduce the iron loss owing to stress during shrinking of a frame and stator core. In step 1, the shrink fit process was applied to a frame and stator core, considering the manufacturing tolerances through three-dimensional modeling. Thermal-structure finite element analysis was performed to apply the same conditions as those in the shrink fit process. The shrink fit was expanded by applying heat to the frame, followed by natural cooling to calculate the contact stress between the frame and the stator core. In step 2, the same contact stress as that in step 1 was derived using structural analysis through two-dimensional modeling of the frame and stator core without tolerances. The contact stress was calculated by applying the equivalent thermal expansion coefficient of the frame, and it was confirmed that the manufacturing tolerance and maximum stress intensity are linearly related. In step 3, electromagnetic analysis was performed at the rated operating point of the 2.2-kW induction motor using the model obtained in step 2. The magnetic flux density distribution of the stator core was derived via electromagnetic analysis and the iron loss, including the stress distribution, realized in step 2. The iron losses obtained under different conditions, including the stress of the stator core owing to the shrink fit tolerance, were compared, and the effectiveness of the shrink fit tolerance required to achieve a motor with high efficiency was evaluated.