Related To Testing Phase To Ground Fault In The Distribution System

Distribution system are universally the non-solidly earthed networks, and the single-phase to earth fault happens most frequently in the power system with ungrounded neutral. However, in the small current grounding power system, when the single-phase to earth fault occurs, because the amplitude of steady state current is small and intermittent arc ground, fault line selecting is very difficult. Several methods have been developed to solve the problem, but none of them can perform perfectly under various fault conditions. For detecting the single-phase to earth fault line quickly and reliably is an important issue in the distribution system protection. And the study of fault location becomes more and more important with the requirement of improving the reliability of power supply and the fast development of the distributed power system automation. So much attention is paid to the problem of discriminating the faulted line or bus in the power system with floating neutral.Aiming at the problem of fault line selection, this paper reviews systematically the existing theories about fault line detection of the neutral indirectly grounded system, and then point out their defect and drawback. At the same time, the steady and transient feature of single-phase-to-ground fault in various types of neutral injecting grounded system is analyzed and simulated, this provides theoretical basis for the research on new fault line selection algorithm. Comparison shows the injecting current method (S method) is a preferable fault line selection method. It does not directly use the steady or transient signals in the lines, so overcomes defect of those methods based on such signals in the lines. Rooting in the S method, this paper use the fault phase current of every line after fault as a selection criterion, and use the correlative detection algorithm to perform fault line selection.It is known that when the transition resistor is too large, we can't choose fault phase only by the lowest one. This article deduces the regularity of three phases following by the transition resistor, and gives a new method of choosing the fault phase. At the meantime, the article Analysis the relationship between residual voltage and transition resistor, this way we can reflect the transition resistor by the residual voltage.In order to detect and abstract the injected signal, this article puts forward a new method based on a principle of correlation detection algorithm. Providing two orthogonal correlation signals, which multiplicities and integrates the signal received by sensor, then we can abstract the injection signal. This filtering method is simple, is strong to anti-interference. The result of simulation shows that this method can complete the detection of injected signal, and chooses the fault line. We use the magnitude and phase of the injection signal filtered out by correlation filter algorithm to choose fault line. But when the transition resistor is too large we can't the right line. For this reason this article analysis tolerance of the magnitude of the injection signals to transition resistor. In order to overcome this shortcoming, this article improves the method to use phase information to improve the collection of fault line.Simulation of fault line selection in neutral indirectly grounded system is performed in MATLAB. In the simulation, parameters such as grounding position, switch angle, grounding resistance, grounding distance, are all taken into consideration. Results indicate that the new algorithm is accurate and reliable.