Based On The Injection Of Small Current Grounding System Single-phase Ground Fault Location Method

Neutral point non-effectively grounded system or neutral point earthed via arc-suppression coil is wildly adopted by medium-voltage power distribution network in our country. Single-phase grounded fault happens most frequently in the non-solidly earthed network with the probability up to 80 percent .When single-phase to earth fault occurs in a non-solidly earthed network, the fault current is small and the three phase line to line voltages are still symmetric since no short-circuit loop is formed, the load can keep on running for a period of time. But when the fault happened, the non-faulted phase voltage would increase and intermittent arc grounding would lead arc over voltage, and the insulation would be damaged in long time running, therefore the system result in more serious phase-to-phase voltage. So single-phase to earth fault should be removed immediately. In case of the fault can't be removed in time, the fault line and fault point should be detected quickly. The fault device should be removed as soon as possible after the necessary load transferring.When single-phase to earth fault occurs, open line method is often used to detect the fault line and artificially searching line method is often used to locate the fault point. Open line method need carry on many switching operation, usually cause many electric users power-off, and artificially searching line method would drain on huge manpower and material resources. Both old methods are unfit with the high automatically electric network contemporarily. Researchers all over the world have made the enormous efforts for a long time, but there is not a satisfactory result so far. Although distribution network's lines are not as long as transmission network's lines but have the features of many offsets and extensively covering area, so it is very difficult to locate fault point. Moreover, with the increasing power system and the high demand to the quantity of electricity power, right and fast location of fault point method need be developed.Nowadays, S-injection method is the most useful method to locate fault point. Many theories based on injection method have obtained well effect and many relays based on injection method have been used in many distribution networks. Based on the injection method and communication technology, this paper put forward the fault location method of single-phase to earth fault. We designed fault location system based on GSM-SMS communication technology, and have obtained well effect. According to the using of the concrete project, this paper illustrates the validity and feasibility of the method. About the question in practical application, this paper analyzed part of the problem and put forward some solutions.In this paper we developed detector of injected signal based on analog method. By using integrated filter chip UAF42 to replace originally separate chips; using high performance, low -cost digital chip of MSP430 serials, and using digital filter improve the accuracy of detecting injected signal; using SIEMENS MC3S communication module based on GPRS system we increased the speediness and reliability of the information transforming. The improved injected signal detector would be put into practice operation in the near future.