Rotor-bearing system dynamics under dynamic air gap eccentricity

The goal of this study is to solve the problem of the condenser’s rotor violently vibrating due to the unbalanced magnetic pulling force (UMP) caused by the dynamic air gap eccentricity of the condenser. To do this, the UMP is theoretically calculated and simulated. The results show that the UMP is a force whose main component is in the natural frequency and that its magnitude is directly proportional to the eccentricity. The modal analysis also shows that increasing the stiffness of the bearing causes a higher critical rotor speed, with the bearing stiffness interval of 1×10⁶ N/m to 1×10¹⁰ N/m experiencing significant changes. The explanation is that the rotor is in a mixed mode, with rigid mode dominant or bending mode dominant when the bearing stiffness is between 1×10⁶ N/m and 1×10¹⁰ N/m. The critical speed is not significantly affected by the bearing damping. The UMP is put on the rotor surface in a harmonic response analysis. The condenser’s rotor is discovered to have a noticeable amplitude peak close to the intrinsic frequency. It is discovered that the amplitude peak decreases as bearing stiffness increases, increases as eccentricity increases, and decreases as bearing damping increases. The first-order force transfer rate peak of the bearing grows and then stabilizes as bearing stiffness increases, but the overall force transfer rate keeps rising. The results demonstrate that condenser rotor vibration can be mitigated by modifying bearing stiffness, damping, and decreasing eccentricity.