Research On Traveling Wave Fault Location Algorithm For 10kV RABCTL

In recent years,the development of high-speed railway is very rapid.Railway transportation has become one of the most important engines to promote the rapid development of China's economy.10 kV railway automatic blocking and continuous transmission lines(RABCTL)is an important part of railway transmission system.However,due to the complex geographical environment along the railway,various kinds of faults often occur.In order to find faults quickly,reduce the difficulty of staff patrolling,and reduce the blackout time,it is necessary to locate faults quickly and accurately so as to eliminate the threat of faults in the shortest time.Cable—overhead hybrid transmission lines are more and more applicated in the 10 kV RABCTL,and its fault location is very difficult.In this paper,the problem of fault location for hybrid lines is studied:(1)Generation mechanism and fluctuation process of traveling wave.Firstly,by analyzing the transient fault process of power system,the origin of traveling wave is revealed from the perspective of microsecond level.The wave process of traveling wave in a single lossy transmission line and three-phase conductor shows that the traveling wave speed is fixed for a given frequency and line parameter,that is to say,traveling wave propagates on the transmission line with a constant wave velocity.The traveling wave will be folded and reflected at the discontinuity of the wave impedance,and the wave velocity under different wave impedances is generally different.These characteristics are the inherent characteristics of traveling wave and the theoretical basis of traveling wave fault location.Secondly,the basic principle of wavelet transform and the modulus maximum theory of wavelet transform are studied to identify the fault traveling wave head.Finally,in order to apply the fluctuation theory of single conductor to three-phase lines or even multi-segment lines,it is necessary to use the phase-mode transformation theory to achieve decoupling.(2)Fault location algorithms for cable-overhead hybrid linesFirstly,the applicability of single-ended traveling wave method in hybrid transmission lines is studied.Because the traditional single-ended traveling wave method has the disadvantage of misjudgement of fault points.Aerial-mode and zeromode traveling wave velocities are different,and the time to reach the same measuring end is successive.Based on this,a single-ended traveling wave ranging method with time difference of modulus-wave velocities is proposed.Secondly,three kinds of hybrid traveling wave ranging algorithms,i.e.time difference method,generalized wave velocity normalization method and virtual fault point projection method,are proposed.The formula of traveling wave fault location with arbitrary multi-segment hybrid lines is deduced,which takes the time difference between two ends of fault initial traveling wave arriving line as independent variable.The algorithm of the two-terminal traveling wave fault location for hybrid lines is unified.It is noteworthy that the proposed algorithm only needs to identify the initial traveling wave head of the fault,and does not need to consider the impact of the fault traveling wave on the fault point and the reflection wave at the end bus.Finally,a real-time simulation model is established by using MATLAB/Simulink software to analyze the impact of different fault types on traveling wave waveform and verify the accuracy and effectiveness of the proposed methods.(3)Factors affecting the accuracy of traveling wave fault locationSome factors affecting traveling wave fault location are analyzed,such as traveling wave refraction,reflection,thermal expansion and contraction effect of transmission lines,and synchronization accuracy of two-terminal clocks.It is concluded that the main reason affecting the magnitude of traveling wave is the refraction of traveling wave,while the length of the line will change after thermal expansion,but it has little effect on the accuracy of traveling wave ranging.The distance error of hundreds of kilometers will be produced when the two-terminal clock differs by 1 ms,which is the main reason affecting the accuracy of traveling wave fault location.