Distributed Fault Location Theory And The Key Technologies For Transmission Line

Fault location with high accuracy and high reliability is one of the major guarantees for thesafety operation for modern power grid. Although traveling wave location technology is widelyused, there still remain problems that will negatively impact its effectiveness and reliability such asthe detection of weak traveling wave signals, the recognition between reflection waves from faultpoint and from the end bus bar, the identification of lighting interference. In this paper, thepropagation characteristics of the fault current traveling waves in transmission lines are analyzed tosolve the above problems, and a new distributed fault location method is proposed which containsrecognition between refraction signal and reflection signal, confirmation of traveling wavesingularity, and identification of lightning interference. A set of distributed fault location device isdeveloped and has been successfully applied in the demonstration project. The main work and resultare as follows.The traveling wave sequences consist of fault traveling wave, its refraction and reflection waveThe arrival time regular pattern of traveling wave sequences is studied. And the conclusion has beenreached that when a fault occurs at any point of the transmission line, the corresponding detectionpoint can always be found such that the first three traveling wave can be uniquely determined. Twomethods are proposed to determine the fault interval respectively. By calculating the degree ofdeviation of the power frequency fault current, a fault interval at inner section can be detected. Andouter section fault interval can be determined according to the time difference of first wave energyand modulus of current traveling wave. Furthermore, three distributed fault measuring methods areproposed including the both ends symmetry method, the midpoint dominant method and four pointscombined method. The work principles of the above three methods are explained and accuracy ofthose methods is proved by simulation.Binary recursive singular value decomposition (SVD) is firstly introduced to the field of faulttraveling wave singularity detection. Digital experiments are designed to compare the performancedifferences among binary recursive SVD,3B-spline wavelet and db2wavelet. According to theexperiments, binary recursive SVD has unique advantages such as compact support, symmetry andhigher order vanishing moments. Linear relationship is found between amplitude of singular pointpulse and mutation amount or slope. Correctness of the above conclusion is proved throughexperiments. The iterative SVD noise reduction method is proposed and is proved correct bysimulation experiment. Singular points linear offset phenomenon is also found in iterative SVD noise reduction.Based on the law of transmission line fault (caused by lighting or line itself) boundaryconditions and traveling wave propagation, the correspondence relationship of three phase travelingwave polarity under conditions of lighting and line fault is analyzed. Then the method to recognizeback lightning flashover of transmission line is proposed based on the polarity difference of threephase traveling wave. Furthermore, shielding failure recognition method is developed based onrevised wave energy ratio in short-time window according to the energy change differences betweenshielding failure and line fault. The above theory is proved correct through experiments. Forconditions that lightning point and flashover point are inconsistent, judgment method andcorresponding measurement method are proposed based on traveling wave distance betweenmeasuring point in short-time window. The correctness of these methods is also proved throughexperiments.Both the theoretical and the empirical analysis are applied on the output power characteristicof the electric coil, and the proportional relationship (when electric coil is working in linear interval)between the output power and the primary current is revealed.Moreover, the output power of coil isalso in proportion to sin(2), where is the phase difference between the primary current and themagnetizing current. In the mean time, it is also found that the output power value is decided by theconduction angle.According to the output circuit load changing characteristic and the results above,a novel design is proposed to gain a stable rated output power through getting a maximum outputpower on the electric coil with maximum power tracking when the load is low, and through gettinga limited output power with power controlling when the load is high. Experiments show that thisdesign can achieve a2W stable output power on energy source when the measured current is inrange of20-2000A.Based on the theoretical foundations above, a distributed fault location system is implemented.Furthermore, experimental platforms are built in respect of both sensors and fault location device.And experiments show that the performance of the distributed fault location system is consistentwith the theoretical analysis.