The rotor winding inter-turn short circuit fault will generate an even number of and fractional harmonic unbalanced current components related to the number of pole-pairs and stator winding configurations in stator loops. Considering the above situation

the expression of the unbalanced magnetic pull(UMP)in the coordinate axis direction of stator Cartesian coordinates is derived based on the harmonic magnetomotive force(MMF)caused by the harmonic component of unbalanced current. Secondly

according to the characteristics of the stator and rotor MMF

the expression of frequency of UMP is obtained and a complete characteristic analytic method for UMP under a fault is formed. This method has been applied in the rotor inter-turn short circuit fault analysis in non-salient pole generator prototypes with a different number of pole-pairs. The numerical result of the rotor electromagnetic force in a fault is calculated by the field circuit coupling of ANSOFT software. Simulation results are consistent with the findings of theoretical analysis

which proves the correctness of this method. Both theoretical analysis and simulation results show that generators with a different number of pole-pairs and stator winding configurations will have UMP with different harmonic characteristics

which lays the foundation for fault monitoring by merging electro-mechanical information. This work is supported by National Natural Science Foundation of China(No. 51307005)and Fundamental Research Funds for the Central Universities(No. 2015YJS149

No. KEJB15016536

No. KERC14003536).