Analysis of Mechanical Losses in a Squirrel-Cage Induction Motor Induced by Different Types of Eccentricity

Rotor eccentricity in electric machines, caused by manufacturing tolerances and rotor aging, is an inherent and unavoidable phenomenon. This eccentricity disturbs the symmetrical distribution of the magnetic field, leading to an Unbalanced Magnetic Pull (UMP) and increased bearing friction losses. This study investigates the impact of static, dynamic, and mixed types of rotor eccentricities on the mechanical losses in squirrel-cage rotor induction motors under no-load conditions. The airgap flux density was first calculated using the Magnetomotive Force (MMF) permeance method, considering multiple armature reactions. The UMP caused by the eccentricity was then determined using the Maxwell stress tensor method. The analytical results for the UMP were employed to estimate the mechanical losses, which were subsequently validated through experimental measurements. The results clearly demonstrate that the presence of rotor eccentricity substantially increases the mechanical loss component in motors, directly impacting no-load losses and consequently reducing operational efficiency. The findings underscore the critical influence of rotor eccentricity in degrading motor performance through increased friction and vibration. This study provides essential guidance for optimizing induction motor design, monitoring and maintenance to enhance reliability and efficiency and mitigate losses.