基于可控短路技术的小电流接地选线方法研究-电力系统及其自动化专业论文.docxVIP

三峡大学硕士学位论文 三 峡 大 学 硕 士 学 位 论 文 PAGE III PAGE III 二种选线判据比第一种判据更有效。 关键词：配电网 小电流接地系统 真空触发开关 可控短路 故障选线 Abstract Neutral non-effectively grounded systems are widely adopted for power distribution systems in China, because of its higher power supply reliability. Neutral effectively grounded systems can produce sufficient faulted current magnitude to allow sensitive and selective relaying with feeders and bus-tie breakers after ground fault. When a ground fault on one phase occurs, the neutral non-effectively grounded systems produce small faulted current. It makes no effects on the normal operation in a period of time. Although the faulted line does not need to be eliminated immediately after ground fault, long period of fault status is dangerous to the safety of the systems. However, the identification of the single-phase to ground faulted line in neutral non-effectively distribution systems is a difficult problem due to its very small faulted current. The problem of faulted line identification in neutral non-effectively distribution systems has not been well solved for a long time. Up to now, many methods of faulted line identification have been proposed. But every method has its field of application. When the fault resistance is relative great, the accuracy of faulted line identification is lower. This paper firstly introduces the basic principle and problem of every method for faulted line identification. Then the paper introduces the main connection modes of the neutral in distribution systems, and analyzes the state electric characteristics when a ground fault on one phase occurs in ungrounded systems and resonant grounded systems. These are the theoretical basis of the criterion for faulted line identification. Due to the characteristic that the small faulted current is hard to be detected, new method based on controllable short-circuit technique is proposed in this paper. It can make the neutral grounded temporarily by controlling triggered vacuum switch (TVS)