【作者】 杜萍；

【导师】 张庆超；

【作者基本信息】 天津大学 ， 电力系统及其自动化， 2009， 硕士

【摘要】 中性点非有效接地系统被广泛应用于我国中低压配电网络,在此系统中单相接地故障是主要的故障类型。发生故障时在接地点故障电流不太大的情况下,电力系统可以带故障运行一段时间,系统有较高可靠性。但这种接地方式也存在缺点:故障电阻的存在、线路参数(特别是零序参数)不准确、测量装置存在误差等再加上本身故障电流很小,使测距的精确度降低。这样就降低了供电可靠性,故找出一种新思路使其能更准确有效地判断故障点具有重要意义。接地故障中,零序阻抗和大地电导率存在直接联系,其值往往随着土壤的湿度、盐度等变化而变化,并非为一定值,故很难测得故障发生时刻的精确值。本文在搜集统计中国各个地区多年土壤湿度的基础上,推导计算并分析了零序阻抗在不同地区,不同时间段的分布。Monte Carlo方法是以概率统计理论为指导的一类非常重要的数值计算方法,其通过使用随机数(或更常见的伪随机数)来解决很多计算问题。本文提出了应用Monte Carlo进行故障测距的新方法。该算法利用零序阻抗的统计信息及其分布规律,求取故障距离的某些数学特征,使在零序阻抗在有大范围变化的情况下得到的测距精度更高。本文提出的算法基于故障线路的建模及Monte- Carlo方法。这种算法不仅能算出故障点,也能求出另一个重要信息,即短路最可能发生的线路段。更多还原

【Abstract】 Non-direct grounded neutral system has been widely used in low and medium voltage distribution system in some countries and the single phrase to ground fault is the main one of this kind of system. When the fault occurred, if the value of the fault current is not too great, the power system can keep operation for a while with the fault. Therefore, this kind of system brings strong power supply reliability. However this system also has a huge disadvantage that the accuracy of fault location is low because of the fault resistance, inaccurate line parameters (especially the zero-sequence impedance), errors of measuring device and the low fault current by its own, which reduces the power supply reliability. So it is necessary to find some ways for the fault location detection.In the phase-to-earth fault power system, the value of zero-sequence impedance is directly related to the earth conductivity. When the soil moisture and salinity change, the value of this impedance is different too. So it is hard to determine the exact value when the fault occurred. The value and distribution of zero-sequence impedance in different areas and periods both are calculated in this paper based on the full-scale soil moisture data.Monte Carlo is an important method that is based on the theory of probability and statistics, which utilizes random number (pseudo-random number is common) to solve many calculative questions. The paper presents a new approach for calculation of fault location. The proposed algorithm utilizes statistical information about the zero-sequence impedances and the distribution laws of these values to get the numerical characteristics of fault location, which results in more accurate fault location for lines with a great interval of the zero-sequence impedance. This algorithm is based on modeling of the faulted line and the method of Monte Carlo. It calculates not only the expected value of the distance to the fault location, namely, the length of the line segment, where short circuit may have occurred.更多还原