Research On Single-phase-fault Line Selection And Location For Small Current Neutral Grounding Power System

The small current grounding adopted by the neutral distributionnetwork cannot cause the trip immediately, but if it works with fault for along time, greater faults will be made. Considering the fact that the signalof the fault current caused by this way of grounding is weak, thecharacteristics of the fault are unnoticeable, and the fault is veryvulnerable to environment. It’s rather difficult to locate and select thefault line. If the single-phase ground breaks down, it’s hard to locate thefault line. Therefore, it’s a difficult problem to locate and select the faultof the small current grounding system.The origin of this paper is from cooperation between colleges andenterprises. The thesis includes the following parts.1.With the grounding way of neutral point as the objective of theresearch, a deep analysis is made to explore features of transient andsteady state fault characteristics when it breaks down, based on which thethesis makes the criterion of the types of faults according to the changesof voltage, including the phase voltage and voltage of neutral in thesingle-phase grounding, and further builds the simulation model to testifythe criterion.2.Based on traveling wave fault location algorithm of wavelettransform, the method extracts the fault time and calculates the distance,and establishes the simulation model. Results show that such method is feasible when there are changes of the location of fault and groundresistance.3.The thesis proposes an improved HHT method of selecting fault line. A simulation is made by testing with the different neutral point grounding mode, voltage fault initial angle, transition resistance and adding noisesignal, which results show that such HHT method has the followingfeatures: the ability to capture the zero sequence current mutation,thereliability to fault location and the practicality of the computing method.