Research On Traveling Wave Fault Line Selection Technology For Non-solidly Grounding System

Most of the existing wave fault line selection methods for non-solidly grounding system only focus on the fault information of the first head of traveling wave.Because of the length of the lines in non-solidly grounding system are short and the number of the feeder is much,the fault traveling wave will have a complex refraction and reflection process in a short time,it cannot select the right line without accurately identifying and capturing the first head of traveling wave.In view of the shortcomings of the existing methods of traveling wave line selection,by analyzing the traveling wave propagation process of non-solidly grounding fault,proposed a fault line selection method for non-solidly grounding system based on the similarity of the traveling wave waveform.The main work of this paper is as follows:1.This paper introducing the basic principles of traveling wave fault selection for non-solidly grounding systems.Deeply analyzed the dynamic propagation process of fault traveling wave based on the actual line structure of the non-solidly grounding system,summarized the shortcomings of the existing methods of traveling wave line selection.Summarized the similarity relationship between traveling wave current in metal sheath grounding wire and zero mode traveling wave current for three-core cable lines which is widely used in medium and low voltage distribution network.2.By analyzing the process of refraction and reflection of traveling waves,summarized a new idea of fault line selection based on the comparison of traveling wave waveform similarity.Proposed fault line selection method for non-solidly grounding system based on the comprehensive similarity comparison of traveling waves waveform on the basis of analyzing the time-frequency energy information of traveling waves.This method extracted the time-frequency energy information of fault traveling wave current by S-transform firstly,then calculated the similarity of traveling wave shape through the time-frequency information,finally,selected the fault line by calculated and compared the comprehensive similarity coefficient of traveling wave waveform.3.Proposed a fault line selection method for non-solidly grounding system based on the comprehensive distance comparison of traveling wave waveform on the basis of analyzing the similar relationships of traveling waves.This method measured the similarity relationship between traveling wave by the modified Hausdorff distance between the transient fault traveling wave waveforms,and then calculated the traveling wave waveform comprehensive distance of each line and other lines according to the modified Hausdorff distance of fault raveling wave,finally,selected the fault line by comparing the traveling wave waveform comprehensive distance.4.This paper built a fault simulation model of non-solidly grounding system at PSCAD simulation environment and processed the simulation data in MATLAB.By setting different types of fault simulation conditions,discussed the influence of fault location,transition resistance,neutral grounding mode and noise for the fault line selection methods.The validity of the proposed method is further verified by the field measurement data.Simulation and measured data analysis shows that proposed methods can effectively compensate the shortcoming that the existing traveling wave line selection method only focus on the fault information of the first head of traveling wave,and can make full use of the transient traveling wave fault information,and is not affected by the neutral point grounding type,fault location and transition resistance of the system,and the line selection results are accurate and reliable,provided a new idea for traveling wave fault line selection of non-solidly grounding system.