A comprehensive study on electromagnetic torque and rotor UMP based on an improved 3D static air-gap eccentricity model

Static air-gap eccentricity (SAGE) is a common fault in generators. Current researches primarily focus on the parallel SAGE types, while the inclined static air-gap eccentricity (ISAGE) has been rarely investigated. This paper proposes an improved air-gap eccentricity model and presents a study on the electromagnetic-mechanical properties in synchronous generators under typical ISAGE running conditions. Such electromagnetic-mechanical properties include not only the magnetic flux density (MFD) variations, but also the mechanical responses of the electromagnetic torque (EMT) and rotor unbalanced magnetic pulls (UMP). The typical ISAGE factors include: 1) a varied rotor inclined angle theta, and 2) different values of axial inclined distance z (indicates the offset combination case of the two rotor ends). This work is based on the MFD analysis calculation. Theoretical analysis, finite element analysis, and experimental study are carried out, respectively, by taking a 5 kVA two-pole prototype generator as the study object. It is shown that the electromagnetic-mechanical properties of the generator will change when the inclined eccentricity occurs. The EMT, and the rotor UMP as well as the vibrations will increase as the rotor inclined theta and z increase. Specifically, the 2nd harmonic has the most significant variation.