Electromagnetic vibration characteristics of an eccentric rotor with a static load

An eccentric rotor does not only occur with dynamic loads, but also has vibrations with static loads. A unified formula is given for the air-gap length for an eccentric rotor considering both the dynamic and static eccentricities. The unbalanced magnetic pull (UMP) of the rotor is calculated numerically. Differential motion equations are given for the rotor system for the effect of UMP, static load (gravity), and unbalanced mass excitation. The rotor shaft orbit and displacement spectra are analyzed for a dynamic eccentricity and a mixed eccentricity with a static load. The direction and magnitude of the static eccentricity are related to the vibration characteristics of the rotor system. The results show that the static eccentricity angle affects the rotor shaft orbit and makes the displacement frequency component amplitudes vary periodically. A harmonic appears at four times the rotating speed with increasing static eccentricity. The effects of a static load on the rotor system can be regarded as a static eccentricity in the direction of the load.