Research On Transient Protection Of Traction Network Of Through-type In-phase Traction Direct Power Supply System

The construction of high-speed railway network is becoming more and more important in the national economy.The existing traction power supply method has electric phase separation links,which restricts train operation;meanwhile,there are problems of harmonics,negative sequence and load imbalance.The penetrating in-phase traction power supply system can well solve the problems of negative sequence and equal power points.The existing traction network mainly adopts protection based on power frequency electrical quantity,and transient quantity protection has made many achievements in the field of power system transmission and distribution.This paper applies the transient protection to the related research of traction network protection.The paper applies frequency domain model of the traction network to analyze the frequency characteristics of the traction network transmission line.the concept of "traction network line boundary" is proposed based on the connection mode between the traction substation and the line,the "line boundary" by the capacitance at Traction Substation exit and the outer 2m line are composed.Discussing further the attenuation characteristics of traction network lines and line boundary to fault transient components found that: the transient components of high frequency will attenuates as they through the traction network line and its boundary;the attenuation of high frequency of transient components is obvious as the line longer;The attenuation of high frequency by the boundary of the traction network is always greater than the attenuation of the line because the distance between the substations is short.In this paper,a single-ended protection scheme for traction network of in-phase traction power supply system using multi-resolution wavelet singular entropy and support vector machine is proposed.The fault direction is judged by the difference between the forward and reverse fault current abrupt characteristics.The capacitor at the exit of the traction substation is connected in parallel to the traction network,which exhibits low impedance characteristics to the high frequency signal.The high frequency current signal from outside the area is attenuated after passing through the capacitor and the line,and thesignal complexity is significantly different from that in the area..Based on this feature,the wavelet singular entropy of the transient current signal obtained at the protection installation in the fault zone is used as the eigenvector of the support vector machine,and the existing data training is used to form the SVM classification model,thereby distinguishing the positive zone from the outside?malfunction.This paper proposes a traction network protection scheme that uses the similarity of the current waveforms at both ends of the line.First,the transmission characteristics of the fault current waveform are studied.From the perspective of the fault current propagation,reflection process,attenuation degree,and polarity,the line is analyzed.Correlation and difference of current waveforms at both ends of the line when internal fault and adjacent line fault.After synchronous current squeeze wavelet transform,the cosine similarity is used to characterize the correlation of the waveform.In the case of a fault in the area,the timing of the fault current reaching the two ends,the reflection process,and the degree of attenuation are approximately the same.The polarity conversion direction is the same,and the waveform is similar.The degree difference is large,the polarity change direction is opposite,and the waveform similarity is low.Using the cosine similarity to construct line protection criteria can quickly and accurately identify internal and external faults.Simulation results show that the proposed algorithm can better meet the requirements of quick-moving,selectivity and reliability,and is not affected by the transition resistance and the initial angle of failure.