Study On Single-Phase Erath Fault In Small Current Grounding System

Neutral point non-effectively grounded modes are widely used in power distribution network in China. These modes can improve the reliability of power suppy. When a single phase to ground fault occurs, the current of the grounding phase is much smaller than the load current and three-phase line voltage can still keep the symmetry. So the system can run with faults for a while. But the fault phase voltage poses a serious threat to the system. In order to avoid the expansion of the scope of the accident, the fault must be located and removed quickly. The main research content of this paper is the problem of fault line selection and fault location.Firstly, this paper do an in-depth research on the steady and transient characteristics of the systems when a single-phase ground fault occurs in them. The results show that the transient and steady characteristics are both contains a large number of fault information, but the steady values are very small, so it will lead great error by using them. The transient information of the systems are more obvious and not affected by the non-effectively grounding method, therefore the use of transient characteristics of lines is more significance. The wavelet transform is a signal analysis tool, it can decompose the signal into different frequence bands, which is conducive to extract the transient fault information from the feature frequency band. The research on the theory of wavelet transform provides a theoretical basis for the method of selecting the fault line. Finally the simulation examples show that the method is applicable to the neutral non-grounded system and neutral point via arc suppression coil system.The structure of distribution networks is more complex, when the fault line is selected, the fault position is alse needed to locate. This paper proposes the use of improved plant growth simulation algorithm and the bat algorithm to locate the faults. Taking into account the fault information is easily affected by various environmental factors, So a reasonable mathematical model is established. It can make use of the PGSA and BA with fault tolerance. The simulation results show that the methods can accurately locate the fault section in the conditions with distortion information or non-distortion information.