The Research On Fault Line Selection And Section Location Method Of Single-phase Grounding Fault In Distribution Network

Single-phase grounding fault is the fault with the highest probability in the distribution network,accounting for 80%~90% of the total fault.The fault identification and determination are urgent problems to be solved in the relay protection of distribution network.With the expansive size of urban distribution networks,the proportion of cable lines will increase,and the current of ground capacitance of the power distribution network will also increase.If faults are not eliminated in time,longterm faulty operation may lead to further expansion of the fault range.The possibility of secondary faults such as insulation breakdown and phase short-circuit occurs.For decades,many domestic and foreign experts and scholars have paid a lot of effort.However,from the point of view of field operation results,there is still no product that can completely figure out line selection and positioning of single-phase grounding fault.This thesis is based on previous studies.Firstly,through the analysis and concluction of domestic and foreign documents,the existing methods of line selection and positioning are compared,and their application principles,applicable occasions and existing defects are summarized.The model of small-current grounding system was established to analyze the fault transient signal,and the simulation model was built in MATLAB/Simulink.The law of fault signal was summarized from the simulation model through comparing with the theoretical analysis.The principle of the line selection method using phase-ground fault components is illustated.According to the same three phase-ground current increment waveform of a sound line after a single-phase earth fault occurs,the fault phase and non-fault phase before the fault line fault point are different,the characteristics of faults in which the phase-ground current increment waveforms differ greatly,and the line selection criterion based on the construction of the difference coefficient of the amplitude difference and the construction of the relative polarity coefficient based on the polarity difference is proposed,and the fault section is discriminated according to the idea of breadth first search.We verify the correctness of the method through MATLAB method of simulation and calculation for a large number of different grounding situation.A DSP-based section location device was preliminarily designed.By setting up a distribution network static simulation experiment platform,the reliability of the method and design was verified on the platform.This method has advantages in small amount of communication,easily achievement,bootstrap routine.The advantages lay a solid foundation for further study.