Research On Key Technologies Of Non-effectively Grounding System Fault Location

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. 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 detected and removed immediately. The fault device should be removed as soon as possible after the necessary load transferring.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. But S-injection method still needs much manpower to find the fault line. 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.In this paper, S-injection theory is used in the auto-location systems, applying GPRS with the combination of short-distance wireless method for communication from the per-unit to the up-computer. Each unit was placed in the bottom of tower to collect the 220Hz injected signals and transmit them to the up-computer which can determine the fault line and locate the specific fault point. This paper designs the structure of the detection device and control procedures. We select STM32 MCU as a micro-controller because of its low-power, high performance, strong anti-interference. Wireless communications use GPRS and short-distance wireless in the form of combination to reduce the fixed costs and guarantee reliability. The solar-energy battery is proposed to be the main energy for the outdoor per-unit, especially for the everlasting online.This paper analyzed in detail of the location of the detector to be placed. On the basis of analyzing electromagnetic field distribution in the bottom of the overhead line, we can get the current signal attenuation characteristics of the magnetic field and find the best position for the detector to extract the injected signal.Basing on the use of hollow coil sensor detection technology, this paper presented a new technology to measure current and voltage. Choose three points below the line to measure the horizontal magnetic induction intensity and vertical electric field strength. The current and voltage values of line can be deduced from the measured values above. Simulations verified the feasibility of this method.