The third-harmonic voltages at the generator neutral and the terminals, and the phase angle relationship between fundamental frequency zero-sequence voltage and zero-sequence current under different single-phase grounding faults are analyzed. According to that, a phase-angle difference direction element for generator stator grounding fault protection is presented. It consists of two parts: for fault location less than 50% of stator winding from neutral point, the direction function is based on the phase comparison of the third-harmonic voltages at the generator neutral with that at the terminals. But it cannot detect the ground fault direction near the generator terminal (for fault location larger than 50～ of stator winding from neutral point), which can be determined by the phase comparison of the fundamental frequency zero-sequence voltage with fundamental frequency zero-sequence current. Research results show the direction element can detect stator grounding faults with high sensitivity and accuracy.%分析了发电机发生内外部单相接地故障后,机端和中性点侧3次谐波电压、基波零序电压和零序电流之间相角的变化关系.在此基础上,提出基于相角判别的新型发电机定子接地保护方向元件.该方向元件由2部分组成:对距中性点50%以内的定子绕组故障,利用机端和中性点两侧故障分量3次谐波电压的相角值相等且为负值的特点构成;对50%以上范围的定子绕组故障,由于零序故障电压和电流均相对较大,采用零序电压和零序电流相位的关系来识别故障方向.该方向元件构成原理简单,可以与目前现场应用的各种单相接地保护方案配合使用,具有较强的工程应用前景.
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