Research On Segment Location And Branch Identification Of Single-phase-to-ground Faults In Multi-branch Radial Distribution Networks

Distribution system is the last link of power transmission,which is the most closely connected link between power system and users,and plays a pivotal role in power distribution.After the single-phase ground fault occurs in the distribution system,it is very important to locate and isolate the fault quickly to improve the reliability of power supply,which is also an important requirement for the construction of smart distribution system.Taking the multi branch radial distribution system as the research objective,for the permanent ground fault,the transient information after the occurrence of the fault is used to complete the fault section location,and the steady-state information after the small resistance of the neutral point is put into operation is used to complete the fault branch identification,so as to be able to quickly isolate the fault and restore the power supply in the non-fault area.Firstly,the transient,steady-state analysis of the fault feeders in the distribution system under the distributed measuring points is established,and the steady-state and transient characteristics of the zero mode current of each feeder terminal on the feeders after the single-phase ground fault are analyzed under different neutral grounding modes,as well as the distribution law of the steady-state and transient zero mode current of the whole system.Secondly,wavelet analysis is used as a mathematical tool to decompose the transient pure fault component of zero mode current after the occurrence of single-phase ground fault in distribution network,calculate the wavelet transient energy of each sub band,and use the energy factor to represent the energy distribution of the transient pure fault component of zero mode current at each measuring point.The basic principle of fault section location is that the energy distribution of zero mode current at the two measuring points of sound section is similar,while the main energy concentration frequency band of zero mode current at the two measuring points of fault section is generally different.The similarity of histogram is used to represent the similarity of energy distribution to complete the fault section location,and the adaptability of the method is discussed under the conditions of neutral point grounding mode,sampling frequency,fault resistance,fault initial phase angle,current transformer polarity reverse connection,inaccurate timing,branch fault and so on.Thirdly,the chi square test is used to judge the difference of the main energy distribution of the adjacent measuring points,and the chi square test results are taken as the preliminary judgment results of the fault section for special scene,and the amplitude and polarity of the zero mode current are used to verify the results.A multi criteria fusion method is proposed to locate the single-phase to ground fault section in distribution system,so as to overcome the defect that a single criterion may lead to misjudgmentFinally,the steady-state characteristics of sound branch and fault branch of distribution system under different grounding modes are analyzed.In this paper,a branch identification method of single-phase ground fault based on simulation after test(SAT)is proposed.In this method,all branches are assumed to be sound branches.According to the characteristics of capacitor components,the SAT current can be calculated from the steady-state zero mode voltage,and then the waveform matching can be realized by using Hausdorff distance to verify whether the hypothesis is true or not.Finally,the fault branche is obtained.