| Transmission line has the length of thousands of miles and complicated topography.According to the statistics data, the proportion of the power outage times caused bylightning strokes accounts for40%-70%of the total in China, which seriously affectsthe safety, reliability and stability of operation for power system. The traditional way tofind the lightning fault span artificially is time-consuming, which will cause outages insupply and economic losses. At present the lightning protection design is mainly basedon the fixed lightning parameters without considering the influence of landform, towerstructure and others, which cannot accurately reflect its performance. Thus research onthe techniques of lightning location for transmission line, the lightning propagation andparameters inversion, can provide theoretical basis for the differentiated lightningprotection design, accident quick fix, lightning warning and others.Considering the special measurement of the non-contact lightning monitoringsystem designed by our research group, the traditional single-end and double-endmethods are improved and a novel lightning location method is put forward. Thelightning range and sources of reflected waves can be determined according to thearrival time and the polarity of the first wave. By using wavelet transform thecorresponding arrival time can be extracted and the corresponding formula is chosen forcalculation. The simulation and field data show that the method with the error rate ofless than0.5%is preciser than the traditional methods. The error rate of the improveddouble-end method is smaller than that of the improved single-end method. The formeris more suitable for the application.Based on the former study, a distributed lightning fault location method is proposed.Firstly according to the transient current wave polarity differences of three phases, thetypes of lightning are recognized, such as shielding failure, lightning stroke to the towerand the ground wire. Then the lightning stroke range is determined by comparing themodulus maxima arrival time and the polarity of the signals. For the shielding failure,whether the flashover occurs or not is judged based on the time-window energy ratio ofthe traveling wave and the sides of lightning and flashover are distinguished. Combingwith wavelet packet transformation, the arrival time of wave head is extracted forlocating points of lightning and flashover. The simulation results show the method hashigher precision than the improved methods. The single phase transmission line model is established respectively based on thecentral difference, forward and backward difference and characteristic FDTD improvedmodels. Through EMTP-ATP and Matlab, the advantages and disadvantages of eachalgorithm are compared and analyzed. In the time domain, the dynamic capacity modelis adopted to simulate the corona effect. In the frequency domain, the skin effect isconsidered by using the Laplace transformation. The nonlinear lossy model oftransmission lines is established considering all the influence factors, which is provedby the simulation and field data.The nonlinear lossy inversion model of transmission lines is establishedconsidering all the influence factors. The calculation results show that the method cansimulate the waveform of the excitation source well but the lack of head waveamplitude information caused by effects of corona and skin cannot be recovered. Tomeet the demands of the engineering application, the tower shunt effect consideringdifferent kinds of lightning are simulated and analyzed. The variation rule of the towershunt coefficient under different amplitudes and lightning current source models aresummarized.Combing the lightning fault location, the parameter inversion method ofthe lightning stroke point is put forward. |
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