Study Of Automatic Fault Location Techniques For Distribution System Based On Signal Injection Method

While neutral points of transmission system is usually directly earthed, distribution system adopts neutral point unearthed mode or neutral point earthed via arc-suppression coil, which is known as non-solidly earthed network. When single-phase to earth fault occurs in a non-solidly earthed network, the three phase line to line voltages are still symmetric, and the network can keep on running for one to two hours. But the non-faulted phase voltage would increase to 3^1/2 times of original voltage, which would lead to more serious phase-to-phase fault. So it is necessary to detect faulted line and fault location as soon as possible. However, after fault occurs, since no short-circuit loop is formed, the fault current is too. small to detect, so detection of single phase to ground fault in distribution networks is one of the hot interests in the area of power systems.Recently, with the development of Digital Signal Processing, the faulted line selection technique has got great progress, but fault location is still an issue which has to be solved. So far, a variety of proposed location methods have not been applied in practice, or have a low degree of automation. Signal-injection method is one of the most useful methods to locate fault point. This method can locate the fault point accurately, but there are still a lot of problems that remain to be further improved, such as the degree of automation, fault tolerance and performance of devices.Based on the analysis of injection-method principle, this paper built distribution network single phase to ground fault location system, which has obtained good effect in locating single phase fault. In the system, to solve the problem of low automation lever, distribution system location software was developed, using VS.NET as platform, and adopted SQL sever database. The network model construction referred to IEC 61970 -CIM 301 public information modeling standard, and adopted the object-oriented programming design thought. On the basis of partition of distribution system, network topology introduced the breadth-first search algorithm. This method can achieve the entire network topology analysis, simply and effectively. According to position of remote signal detector, automatic locating algorithm added information compensation algorithm. This algorithm finally solves the difficulty of accurate locating when detectors' information is inaccurate or incomplete.Communication between remote detectors and PC software system is another key to locate fault point. Means of communication in this paper add GPRS communication mode on the base of the traditional GSM short message. The developed automatic location system has achieved good results in the field experiment. It can locate single phase ground fault point, automatically and accurately.