Research On Single-Ended Traveling Wave Fault Location Method For DC Transmission Lines Based On Wavefront Information

DC transmission lines across a wide range of regions,complex operating environment,fast and accurate fault location technology,to ensure the safety of users with electricity,reliable operation of the system is of great significance.The traveling wave location method has high location accuracy and is the main distance measurement method for DC transmission line fault location.Traveling wave location method in DC line field application is generally based on the double-end method,supplemented by the single-end method.The single-end method uses only the fault traveling wave signal collected at one-end location device and does not require information from the other end.It can perform fault location when the device at one end of the line is abnormal and causes double-end location failure,thus avoiding system location failure.However,due to the large difference in fault conditions,the fault waveform is complex,and the automatic fault location is difficult.In this paper,the fault distance information is extracted based on the dispersion distortion characteristics of the fault wave head to identify the fault reflected wave head,which can realize the automatic fault location of single-ended traveling wave.The fault initial traveling wave head distortion of DC transmission line and fault distance related,this paper analyzes the DC transmission line traveling wave signal acquisition method,based on the relationship between the fault initial traveling wave head distortion of the line and fault distance,and a single-ended traveling wave automatic location algorithm for DC transmission line based on wavefront steepness and Empirical Mode Decomposition(EMD)is proposed.The specific work is as follows:(1)DC transmission line fault traveling wave dispersion characteristics analysis.In this paper,the fault traveling wave of DC line is indirectly obtained by using the current transformer at the grounding measurement end of overvoltage absorption capacitor.The research shows that the line fault initial traveling wave along the line propagation process occurs in the obvious dispersion distortion phenomenon,and the wave head distortion degree and fault distance related.On this basis,the paper analyzes the influence of fault distance,fault type,transition resistance,and earth resistivity on the traveling wave dispersion distortion.(2)The initial fault distance is calculated based on wavefront steepness.The generalized Logistic function is used to fit the zero-mode wavefront part of the fault initial traveling wave to obtain the waveform distortion parameter——wavefront steepness.The wavefront steepness is different at different fault distances,and the Exp Dec2 function is used to fit the relationship between the fault distance,wavefront steepness,and earth resistivity in order to calculate the initial fault distance based on the wavefront steepness of the fault initial traveling wave.(3)Marking the arrival moment of the traveling wave head based on the modulus maxima.In this paper,the fault waveform collected by the traveling wave loaction device is decomposed by EMD,and the IMF1 modulus maximum is used to mark the fault time when the initial traveling wave and other reflected wave head reach the measurement end.(4)A single-ended traveling wave location method is proposed that integrates wavefront steepness and EMD decomposition of IMF1 modulus maximum.Based on the relationship between the fault initial traveling wavefront steepness and the fault distance of the DC line,the initial fault distance calculated from the wavefront steepness assists in identifying the fault reflection wave head and realizing automatic single-ended traveling wave distance measurement.The simulation model of ±500k V DC line is established in PSCAD / EMTDC,and the results of the example prove the effectiveness of the algorithm.Aiming at the difficulty of fault reflection wave head identification in single-ended traveling wave fault location,this paper uses the secondary side current of the transformer at the grounding measurement end of the DC line overvoltage absorption capacitor to indirectly obtain the line fault traveling wave.Based on the relationship between the fault initial traveling wave head distortion and the fault distance of the DC line,a method of identifying the fault reflection wave head by combining the initial traveling wave front steepness and EMD decomposition is proposed.The method has good applicability under different transition resistance,fault type and earth resistivity.