Fault Analysis And Fault Location Of Mixed-Voltage Double-Circuit Transmission Lines

With the rapid development of Chinese economy and society,the load of regional power grid is becoming increasingly intensive,and the transmission line channels are becoming increasingly scarce.The double-circuit transmission line is widely used because it can effectively save transmission channels and reduce construction costs.At present,in some economically developed areas represented by Shenzhen,in order to improve the transmission capacity,single-circuit transmission lines have been expanded into double-circuit and four-circuit transmission lines,or mixed-voltage double-circuit and four-circuit transmission lines.Among the double-circuit transmission lines,some double-circuit lines adopt the standard construction of different voltage levels,and some lines adopt the untransposition arrangement of wires due to the short length.The resulting asymmetry of line parameters makes the electromagnetic coupling between wires complicated,and the inconsistency of self-impedance and mutual impedance of each phase wire further increases the difficulty of line parameter analysis.The fault analysis and the fault location become more complex.This thesis mainly researches various types of fault analysis and fault location of different types of double-circuit transmission lines.The main research contents are as follows:Firstly,the modal transformation method and related theory of double-circuit transmission lines are described.The purpose and significance of modal transformation are explained by decoupling single-circuit parameters.Based on uniform transmission line equation,the establishment method of modal transformation matrix is deduced,and the common modal transformation matrix used in fault analysis of single-circuit transmission line is introduced.On this basis,combined with the analysis of the structural characteristics of double-circuit transmission lines,the establishment of modal transformation matrix for transposed double-circuit transmission lines and the method of modal transformation are discussed,which lays a foundation for the fault analysis and location of mixed-voltage double-circuit transmission lines.Secondly,zero-sequence mutual inductance between different voltage levels affects the fault current when cross-voltage fault occurs on mixed-voltage double-circuit lines.The construction of mixed-voltage double-circuit lines partially on the same tower is more special,which makes it difficult to analyze the characteristics of cross-voltage fault.Aiming at the cross-voltage fault of mixed-voltage double-circuit lines partially on the same tower,the sequence parameter model of mixed-voltage double-circuit lines partially on the same tower is established and simplified.Based on the improved composite-sequence network,a method is proposed to analyze the characteristics of cross-voltage faults of mixed-voltage double-circuit lines partially on the same tower.Based on the analysis of the sequence parameter model of the mixed-voltage double-circuit lines partially on the same tower and the solution of its equivalent model,the improved composite-sequence network diagram of each type of fault is drawn according to the boundary conditions of each type of fault,and the fault characteristics such as the current at the fault point are solved from the improved composite-sequence network diagram.The simulation results verify the correctness and practicability of this analysis method for cross-voltage fault analysis of mixed-voltage double-circuit lines partially on the same tower.Finally,some short-distanced double-circuit transmission lines are un-transposed,which results in asymmetric line parameters and makes traditional analysis methods such as six-sequence component method ineffective,and a new phase-mode transformation method is needed to decouple the parameter matrix.By improving the standard Karenbauer transformation matrix and using the same and reverse component transformation,the modal transformation matrix suitable for the un-transposed double-circuit line parameter decoupling is obtained.To solve the problem that it is difficult to solve the fault location equation of un-transposed double-circuit transmission lines,a new fault location method based on improved Karenbauer matrix and quantum particle swarm optimization is proposed.In this method,the line parameter matrix is decomposed into the same and reverse sequence components by using the same and reverse sequence component transformation,and then the standard Karenbauer matrix is transformed to obtain the improved Karenbauer matrix suitable for the untransposition line,which is respectively applied to the same and reverse sequence components,and the decoupled modal parameter are solved.Based on the principle that voltage amplitude at both ends is equal,fault location equation is written by using sequence components at each end after line parameter decoupled,and quantum-behaved particle swarm optimization is introduced to solve the equation.The reliability and accuracy of the proposed method are verified by PSCAD simulation.