Multiphase annular brushless excitation systems

with their excellent redundancy

are the most common form of excitation for high-capacity nuclear power units. Since the windings of each phase are concentrated in localized sections of the motor circumference

eccentricity faults can lead to significant imbalance among the phases

resulting in excessive vibration and internal overvoltage in the stator. To investigate the characteristics of static eccentricity faults

starting from the unbalanced air gap permeance after eccentricity

the harmonic features of the stator excitation current that can be measured were derived by analyzing the mutual coupling between the excitation winding and the armature winding after eccentricity faults. Subsequently

electromagnetic transient models with varying degrees of eccentricity faults were simulated

and the results were analyzed in the frequency domain. The harmonic characteristics observed in the armature current

spatial magnetic flux density

and excitation current from the simulations align well with the theoretical analysis. Finally

the validity of the theoretical analysis was further verified through actual field recordings of faulty excitation currents from an operational machine. The analysis method and conclusion of the proposed static eccentricity fault can be applied to multiphase annular brushless exciters with different phase numbers

and the harmonic characteristics of the fault excitation current provide a theoretical basis for the research of static eccentricity fault monitoring.