Fault Analysis And Fault Location For Transmission Lines Under Different Voltage Levels

As economic of China develops, and the grid keeps building, the air corridor is more intense, therefore transmission lines under different voltage levels are more and more. But operation modes of transmission lines under different voltage levels are complex, voltage levels are different, line parameters are asymmetrical, coupling between the lines are complex, bring new challenges for fault analysis and fault location. Therefore it is necessary to analysis the decoupling method, fault analysis and fault location can be realized based on the complete decoupling, which provides the theoretical basis for the operation and protection research of transmission lines under different voltage levels.(1)Based on the new six-sequence component decoupling method of two-parallel lines under different voltage levels, the modification of system impedance method is improved. Partial uncoupling lines are first decoupled into completely decoupled positive, negative sequence and zero sequence by symmetrical component method, classified into system impedance. Then partial coupling lines are decoupled into completely decoupled positive and negative sequence, in which system impedance do not need to be modified. The left uncoupled zero sequence can be decoupled by circumfluence theory, and system impedance of zero sequence need to be modified. The modified zero sequence system impedance of two parallel lines need to be converted to the same voltage level. At last, according to the boundary conditions of interline faults of two parallel transmission lines, Equations are introduced for fault current calculation. Simulation results demonstrate that the new sequence component method is appropriate for fault analysis of partial coupling lines under different voltage levels, and the short circuit analysis and calculation prove to be correct.(2)Based on the Structural characteristics of four-parallel lines under different voltage levels, a new twelve sequence component method is put forward. Four-parallel line under different voltage levels is generally made up of two parallel lines, which is under symmetry parameter. Four-parallel lines are decoupled into completely decoupled same and differential positive and negative sequence components by traditional six sequence component method, system impedance need to be modified to be twice than the original system impedance on same sequence components. System impedance is zero on differential sequence components. The left coupling zero sequence components can be decoupled by circumfluence theory, and system impedance of zero sequence need to be modified. The modified zero sequence system impedance of two parallel lines need to be converted to the same voltage level. At last, according to the boundary conditions of faults of four-parallel lines, the related sequence networks are introduced for fault current calculation. Simulation results demonstrate that the new sequence component method is appropriate for fault analysis of four-parallel lines under different voltage levels, and the short circuit analysis and calculation prove to be correct.(3)Based on the new six sequence component decoupling method of two-parallel lines under different voltage levels, the method of fault location of partial uncoupling lines under different voltage levels is put forward. After the sampling voltage and current data of both ends of the transmission line are decoupled, the voltage and current of both ends of the partial coupling lines can be calculated through the partial uncoupling lines, which can be completely decoupled into the new six sequence component, the fault location formula can be obtained based on that the voltages of fault point calculated by both ends are equivalent, fault location can be realized. Simulation results demonstrate that the algorithm is nothing to do with the fault resistance, fault type and generation mode, and has good prospects.