Study On Single Terminal Traveling Wave Based Fault Location Of HVDC Transmission Lines Based On Mathematical Morphology-Correlation Function

HVDC has developed rapidly in our country these years, but because of the thousands kilometers length of HVDC transmission line and the complicated geographical environment along the line, it’s easy to break, so it is important to locate the fault accurately, and the single terminal method is one of the hot research issues. The key to single terminal principles is that it must detect the second reversed traveling wave caused by faults accurately and reliably and distinguish the nature of it. Traveling wave correlation method is one of the classical algorithm, but because of the time window’s width and some other factors, correlation method does not meet the practical requirements. In this paper, we combined mathematic morphological filtering and traveling wave correlation method to improve the single terminal algorithm’s reliability, accuracy and adaptability in practical application. This article prime task is as follows:(1) Analyze the generating process and wave propagation characteristics of DC transmission lines faults, sum up the relationship between the fault traveling waves, and discuss the two key problems in the practical operation of traveling wave correlation algorithm: the criterion of the correlation function maximum is not reliable enough, and there is no effective way to choose the appropriate time window in advance.(2) Based on the research and analysis to the composition and operational characteristics of HVDC and the fault characteristics, we use electromagnetic simulation software PSCAD to establish the simulation model of high-voltage direct current and fault modules. And the model is simulated in four ways:earth fault, disconnection fault, lightning fault and the normal steady state. Simulation with PSCAD has shown that the model is consistent with the requirements of current transmission system operation.(3) Combined with the characteristics of morphological filtering and morphological transformation, the gradient transformation with the function of morphology filtering has been designed, it has dual structure elements. Then the single-ended traveling wave fault location algorithm is proposed, which is based on mathematical morphology-correlation function theory:first, through the dual structural elements morphological gradient designed in this paper we can separate traveling wave and then find the correlation function curves with traveling wave correlation method, finally proceed correlation analysis so as to achieve transmission line single terminal fault location. This article obtains the fault data through the simulation using PSCAD, and uses the MATLAB software to achieve the algorithm. It takes the single-phase grounding fault circuit as example. The result has shown that this algorithm can resist transition resistance of 100Ω, the error is in 150m, and endure the influences of various types.The single-ended traveling wave fault location algorithm based on mathematical morphology-correlation function theory is feasible. It can endure the influences of fault distances and fault types, and has characteristics of high anti-transition resistance, reliability, accuracy.