The Research On Phase-Mode Transformation And Fault Analysis Of Asymmetry-Parameter Four-Parallel Transmission Lines On The Same Tower

With the development of power system and the shortage of landresources, more and more four-parallel transmission lines on the same tower(FTLT) are applied. But the complicated coupling among the lines, theasymmetry parameters caused by line rotation as well as the complexity ofinter-line faults, all challenge the decoupling of the impendence matrix, faultanalysis and relay protection. This dissertation summarizes the research onphase-mode transformation and fault analysis of FTLT during the author’sgraduate study, and main achievements are shown as following:1. According to the structure characteristics of asymmetry-parameterFTLT, the four zero-sequence components method (FZCM) is proposed forthe totally decoupling. In this method, same direction component andcirculation components with correction coefficients are introduced only inzero sequence. On basis of that, fault component networks for FZCM aregiven.2. Considering the boundary conditions of asymmetry-parameter FTLT,this paper analyze one-phase grounding fault, two-phase grounding fault,two-phase inter-phase fault and three-phase inter-phase fault of single line.The corresponding comprehensive networks are also given. Numeroussimulation and calculation results show that calculation accuracy of faultcurrents is improved.3. According to the differences of boundary conditions, comprehensivenetwork method and equation method are separately proposed for inter-linefault calculation of asymmetry-parameter FTLT. Some typical faults areanalyzed as examples using these methods. And simulation results verify its correctness.4. This paper also proposes a ground-fault distance protection methodbased on FZCM. The compensation coefficients based on four zero-sequencecomponents are applied in zero sequence reactance relay to eliminate theinfluence caused by mutual inductance among parallel lines. Simulationresults show that the coupling between zero-sequence currents has noinfluence on protection coverage, and this new protection method also hasgood sensitivity. So it promises bright application prospects.Finally, the results of the above researches are concluded, and directionfor further study is proposed.