Fault-location Method For HVDV Hybrid Transmission Lines

For its unique advantages, such as no power transmission corridor, easy to acrossthe river and the channel, high reliability, hybrid transmission line as one of the DCtransmission lines, have got a wide range of applications in DC transmission system ofChina. Therefore, the study of hybrid transmission line fault location has importantsignificance to ensure the reliability of power supply and to improve the security andstability of power system economic operation.There are two main factors influencing the accuracy and reliability of travelingwave fault-location, namely the determination of traveling wave velocity and the timewhen the reflected wave fronts arrives. The traveling waves disperse and attenuate duringthe online propagating, which may cause the wave head distortion, affect the velocity ofwave head and the reliability and accuracy of the traveling wave fault-location.The fault-location method based on natural frequency which doesn’t need to identifythe traveling wave fronts, accurately calculate the velocity of the traveling wave, improvethe reliability of fault-location. The traveling wave method and the natural frequencymethod were mutual complementary. Therefore, for the type A hybrid transmission lineswhich are simply connected, in order to improve the accuracy and reliability of theexisting traveling wave method, this thesis proposes two kinds of fault location methodsbased on the time-frequency characteristics of transient traveling wave, which combinesnatural frequency method with traditional single-ended and the double-ended travelingwave method. Firstly, it uses method based on natural frequency to calculate roughlyfault distance, then the time regions of reflected waves are confirmed through thedistance, and the reflected wave fronts are recognized, lastly, accurate fault locationresults can be utilized by traveling wave fault location.For the type B hybrid transmission lines which are complexly connected, it isdifficult to identify and extract the traveling wave, the accuracy and reliability of thetraveling wave method is lower.The amplitude and frequency of the natural frequency arechosen as the characteristics of artificial neutral network(ANN). A novel fault-locationmethod for HVDC hybrid transmission lines based on ANN is presented.The composition and amplitude of the natural frequency are different when thefailure occurred at various locations of HVDC hybrid transmission lines. Hierarchicaldistributed neural network model could locate the fault distance, which is constructed onthe basis of the analysis if there is a "fixed-frequency" in the spectra and the amplitude ofthe dominant frequency. It can improve the training efficiency, speed up convergence byusing PSO algorithm to optimize the weights and bias of BP neural network. Lastly, this paper uses power system simulation software PSCAD/EMTDC to builda model, and the novel fault location algorithm is used to make simulation analysis offault location when line fault has happened on different positions and with differentresistances on the transmission line. A large number of simulation results show that thelocation accuracy of the novel methods raised in this thesis have a significantlyimprovement over existing traveling wave method. Moreover, their reliability andaccuracy will not be affected by fault resistance, fault distance or fault type.