中文摘要：

大型水轮发电机励磁绕组匝间短路故障不仅会使励磁电流增大、输出无功功率减小，还会导致机组振动加剧，影响系统的安全稳定运行。为对故障特征及其机理进行研究，以三峡左岸VGS发电机为例，首先通过分析故障时励磁磁动势及其作用在不均匀气隙产生的磁场性质，得出定子相绕组内部存在分数次不平衡分支电流的特征。以定子支路为基本分析单元推导出分支电流时间谐波次数与电枢反应磁动势空间谐波次数的对应关系，进而得到电枢反应磁场在转子绕组中产生的附加电流谐波次数的一般性通式。最后利用经过实验验证的多回路方法对故障进行定量计算，验证了理论分析的正确性，并基于计算结果对故障的保护进行了初步探讨。提出分数槽水轮发电机励磁绕组匝间短路故障特征的分析方法，为故障在线检测与保护奠定了理论基础。

英文摘要：

In addition to the resulting field current increment and reactive power output decrement, the inter-turn short circuit of field windings in large hydro-generators will also introduce the aggravation of vibration, which jointly affect the secure and stable operation of power systems. In order to study the fault characteristics and mechanisms, the Three Gorges left bank VGS generator is used as example for this study. Firstly the properties of the field MMF and the uneven air-gap field generated by the MMF under fault conditions are studied. It can be concluded that there exist fractional harmonic unbalanced branch current inside each phases of the stator. Then the stator branch can be used as the basic analysis module, the relationship between time harmonic frequency of branch current and space harmonic frequency of the armature reaction MMF can be derived; and the routine general formula of the harmonic frequency of the additional current in the rotor windings produced by the armature reaction field can be obtained as well. Finally faults can be calculated quantitatively using a multi-loop method as verified by experiments, which prove the validity of the theoretical analysis. Based on the calculation results, protection of the faults is also preliminarily discussed. This paper initially puts forward the analysis method of the inter-turn short circuit fault characteristics of field windings in fractional-slot hydro-generators. It forms the theoretical foundation for the fault on-line detection and protection for fractional-slot hydro generators. This work is supported by National Natural Science Foundation of China （No. 50807027）.