Effect of 3D unidirectional and hybrid sage on electromagnetic torque fluctuation characteristics in synchronous generator

This paper presents a comprehensive study on the variation laws of electromagnetic torque (EMT) under static air-gap eccentricity (SAGE) conditions in synchronous generators. Different from other studies, this paper focuses on not only the impact of radial SAGE, but also the effect of axial and hybrid SAGE, on the EMT fluctuation characteristics, i.e., we actually study the 3D static rotor eccentricity. The theoretical analysis model is first set up to study the influence of SAGE on the magnetomotive force (MFD) and EMT. Then, the finite element calculation and the experimental study on the CS-5 prototype generator which is of two poles and 3000 rpm are carried out to validate the theoretical analysis. It is shown that the radial SAGE will increase the dc component of MFD and shift the whole MFD curve and the phase current upwardly, while the axial SAGE will reduce the dc component as well as the amplitudes of both the MFD and the phase current like a compressing operation. In general, no matter in unidirectional or hybrid SAGE cases, the radial SAGE will intensify the EMT ripple and increase each harmonic of EMT, while axial SAGE will play the opposite role. The research conclusion obtained in this paper is potential to be applied as a supplement criterion for the condition monitoring and control of the eccentricity faults.