Characteristics Analysis of Field Winding Inter-Turn Short-Circuit Fault for Large-Capacity Synchronous Condenser Based on Stator Winding Asymmetric Branch Current

The early inter-turn short-circuit fault of field winding (ISFF) occurs between adjacent strands in a single rotor slot, which is a significant safety hazard in the transient operation of the large-capacity synchronous condenser. To realize high-precision detection of early ISFF, this paper proposes a characteristics analysis method of ISFF with the field strand as the minimum unit. This method combines the novel stator winding asymmetric branch connection mode of the condenser. Compared with the fault characteristics analysis method with the field coil as the minimum unit, the proposed method can analyze ISFF characteristics between strands in a single rotor slot and has higher fault detection resolution, which is especially suitable for electric excitation synchronous generators with stator winding asymmetric branch connections. The results show that ISFF occurs in a single rotor slot, the even harmonics components appear in the field magnetomotive force and partial stator winding asymmetric branch current, and the 2nd harmonic component accounts for the largest proportion. Taking the 5 turns ISFF in slot 1 of the 2-pole 3-branch condenser as an example, the 2nd harmonic in the field magnetomotive force even harmonics accounts for 55.15%, and the number of branches with even harmonics components current accounts for 66.67% of the total number of branches. The research results can provide theoretical support for high-precision ISFF detection to avoid fault expansion.