Fault Line Selection And Fault Location For A Single Phase Fault Of Small Current Grounding System

Neutral grounding of power system is divided into two categories:High-current grounding and Small current grounding. Middle voltage distribution power systems in our country are almost small current grounding systems. The single-phase-to-earth fault happens most frequently in the small current grounding system. Due to weak fault current, arc instability and random factors, fault line selection and fault location are always hard problems in small current grounding system. Especially for the problem of fault location of small current grounding system, there are always no reliable fault location method and precision fault location device for single-phase-to-earth fault in small current grounding system.Under this background, on the basis of previous research of fault line selection and fault location in small current grounding system, a method of small current grounding system fault line selection based on wavelet transform and a method of small current grounding system fault location based on signal injection and traveling wave fault location method was proposed in this thesis. The simulation of single-phase-to-earth fault in small current grounding system with MATLAB verifies the effectiveness of the algorithms.The main works of the thesis are shown as follow.(1) The fault characteristics for single-phase-to-earth in small current grounding system are analyzed systematically. This thesis analyzed the steady-state characteristics and transient characteristics of single-phase-to-earth fault in small current grounding system.(2) A method of fault line selection for single-phase-to-earth fault in small current grounding system based on wavelet transform was proposed in this thesis. This method could determine time of fault by transforming the zero-sequence voltage with wavelet and determine line fault line by comparing the magnitude and polarity of wavelet transform of zero-sequence current. It can select the fault line reliably. In the end the simulated results verify the effect of research.(3) A method of fault location of small current grounding system based on signal injection and traveling wave fault location method was presented in this thesis. This method could realize fault section location through injecting a specific frequency signal into fault phase through fault location devices, estimate the fault distance according to the method of traveling wave fault location. In the end the simulated and experimental results verify the effect of research.(4) The fault location device for single-phase-to-earth fault in small current grounding system was designed based on TMS320F2812DSP.