Auto Fault Locating System And Application Techniques For Single-line To Ground Fault Selection In Middle-low Voltage Distribution Networks

In China, the non-solidly earthed neutral is widely used in distribution system. It has the virtue of proving power supply's reliability. 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. But fault location are not solved when single-phase to earth fault occurs due to weak current and unstable fault arc. To date utilities still use manual switching to identify an earthed feeder and eyeballing to locate the fault point in the absence of a more reliable detection method. So, this paper studies automatic fault location in distribution systemNowadays, 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.In this paper, S-injection theory is used in the auto-location systems, applying GPRS method for communication from the per-unit to the up-computer. Each unit can collect the 222Hz injected signals and transmit them to the up-computer which can determine the fault line and locate the specific fault point. In order to decrease the power cost of the per-unit, the emphasized digital filter is used instead of the logical circuits. The filter processes and the anti-interference technology are presented in this paper. Also the software is finished. The solar-energy battery is proposed to be the main energy for the outdoor per-unit, especially for the everlasting online.The S-injection fault located system is tested in the laboratory and proved very good in the field running.