中文摘要：

小电流接地系统单相接地故障选相的传统判据是建立在电网对地参数严格对称的条件下形成的，由于电网不对称度的普遍存在，当电网发生不完全接地故障时，特别是经高阻接地时，传统判据失效。详细分析并给出电网发生不完全接地故障后的零序电压轨迹，根据零序电压变化的特征将平面坐标系分成若干扇区，每个扇区与电网参数“不平衡矢量和”相对应。研究发现，零序不平衡电压处在的扇区不同，随着过渡电导的增加，零序电压的幅值和相位变化均出现不同的特征，可根据零序电压轨迹变化的规律特征，实现单相不完全接地故障相的判别。理论及仿真分析表明，所提方法可有效解决不对称电网发生不完全接地故障相的识别。

英文摘要：

Traditional single-phase-ground fault phase selection criterion in small current grounding system is based on the conditions that line parameters are strictly symmetrical. Strictly speaking, the grid lines-to-ground parameters are not always symmetrical. When single-phase ground fault occurs, conventional method does not work, especially in the case of a large transition resistance. The paper analyzed its mechanism in detail and gave the neutral voltage locus when single-phase- ground fault occurred. The impact of transition resistance to the zero sequence voltage considered, the plane coordinate system was divided into several sectors, and every sector corresponded with the ＂parameters imbalance vector addition＂. It was found that, with the increase of transient conductance, zero-sequence voltage amplitude and phase angle were changed differently with the unsymmetrical voltage in different sectors. According to the characteristics of neutral voltage locus, single incomplete grounding fault could be selected accurately. Theoretical analyses and simulations show that the method can identify the phase of incomplete grounding fault in unsymmetrical power.